MAP602_Experimental Psychology

Contribution of Weber, Fechner, Wundt and Galton 45 quantities mathematically, Fechner sought to establish a general functional relationship between sensations and stimuli of whatever magnitude. In the range within which Weber’s law is valid— Weber’s law states that jnds are proportional to the magnitude of the stimuli—integration yields a function that describes the intensity of a sensation in terms of the logarithm of the stimuli, measured from the absolute threshold. Since the acuity of the sensory apparatus fluctuates from instant to instant and from person to person, thresholds can be defined only statistically. Fechner perfected the experimental strategies that had earlier been used by Weber and by Vierordt, as well as by such astronomers and physicists as Lambert, Steinheil, and Laugier, to determine the degree of uncertainty or the accuracy of measurement in comparisons of stimuli. According to the nature of variation of the stimulus in comparisons of successive sensations, he distinguished three kinds of psychophysical methods of data collection: (1) the method of jnds, in which the difference between the stimuli compared is gradually increased until it is perceptible or diminished until it is no longer perceptible; this is also called the method of limits; (2) the method of right and wrong cases, in which a standard stimulus is compared with randomly varied comparison stimuli; this method is also called the constancy method; and (3) the method of average error, in which a comparison stimulus is adjusted by the subject to correspond to a standard; this is also referred to as the reproduction method. In calculating threshold values, Fechner employed the law of errors formulated by Gauss and Laplace, and in his posthumous Kollektivmasslehre (1897) he set forth the applicability of the law of errors to many other problems in psychology. The Kollektivmasslehre also contains his contributions to correlation statistics. It is the first textbook of statistics to be designed especially for behavioral scientists. Using carefully planned experiments, whose layouts resemble those today used in the analysis of variance, he endeavored to exclude from the calculation of reaction variability, which defines the threshold difference, those constant errors that arise from the particular features of the experimental procedure. Fechner realized that “psychophysics” (his coinage) was an innovation of great importance: he called it a science “in the initial state of becoming,” and his own work for all its scope, merely “a modest beginning of a beginning.” His work was soon taken up by some of the greatest scientists of CU IDOL SELF LEARNING MATERIAL (SLM)

46 Experimental Psychology his time. As far back as 1858, Ernst Mach and Hermann von Helmholtz had begun to experiment on their own, stimulated by Fechner’s preliminary report. Wilhelm Wundt followed in 1862, A.W. Volkmann in 1864, H. Aubert and J.R.L. Delboeuf in 1865, and J. Bernstein and Vierordt in 1868. Of the outstanding specialists in the field of psychology only one remained a skeptic: William James, who as late as 1890 declared that despite all its acumen and all its care, the psychological yield of the Elemente was “just nothing,” not important enough to merit mention in even a footnote. The methods of measurement developed by Fechner are now generally adopted in quantitative experimental psychology, although some of the mathematical implications of his derivations are open to serious criticism (Luce and Galanter, 1963). They are employed with equal success in all sorts of fields and for the most diverse problems. In recent years, the problem of psychological scaling, which Fechner was the first to appreciate and deal with, has again come to the forefront; it has been remarkably clarified and given new depth, especially in the work of S.S. Stevens and G. Ekman (for example, Stevens 1934). Fechner is remembered almost exclusively as a methodologist. The fundamental theoretical postulates he presented in his psychophysics have gone unnoticed and are generally attributed to later authors. Most noteworthy is his working hypothesis of “concrete parallelism,” which assumes an isomorphism between phenomena of consciousness and “psychophysical phenomena,” i.e., those processes occurring in the cerebrum that are directly associated with the phenomena of consciousness. This assumption and its elaboration is usually attributed to Ewald Hering, Georg Elias Muller, Max Wertheimer, and, above all, Wolfgang Kohler, although it was clearly formulated in Volume 2 of Fechner’s Elemente. 2.6 Wilhelm Wundt Wilhelm Maximilian Wundt was a physician, physiologist, philosopher and professor, known today as one of the founders of modern psychology. Wundt, who distinguished psychology as a science from philosophy and biology, was the first person ever to call himself a psychologist. He is widely regarded as the “Father of Experimental Psychology”. In 1879, at University of Leipzig, CU IDOL SELF LEARNING MATERIAL (SLM)

Contribution of Weber, Fechner, Wundt and Galton 47 Wundt founded the first formal laboratory for psychological research. This marked psychology as an independent field of study. By creating this laboratory he was able to establish psychology as a separate science from other disciplines. He also formed the first academic journal for psychological research, Philosophische Studien (from 1881 to 1902), set up to publish the Institute’s research. Fig. 2.3: Wilhelm Wundt A survey published in American Psychologist in 1991 ranked Wundt’s reputation as first for “all-time eminence” based on ratings provided by 29 American historians of psychology. William James and Sigmund Freud were ranked a distant second and third. Central Themes in Wundt’s Work Process Theory Psychology is interested in the current process, i.e., the mental changes and functional relationships between perception, cognition, emotion, and volition/motivation. Mental (psychological) phenomena are changing processes of consciousness. They can only be determined as an actuality, CU IDOL SELF LEARNING MATERIAL (SLM)

48 Experimental Psychology an “immediate reality of an event in the psychological experience”. The relationships of consciousness, i.e., the actively organising processes, are no longer explained metaphysically by means of an immortal ‘soul’ or an abstract transcendental (spiritual) principle. Psychophysical Parallelism Influenced by Leibniz, Wundt introduced the term psychophysical parallelism as follows: “wherever there are regular relationships between mental and physical phenomena the two are neither identical nor convertible into one another because they are per se incomparable; but they are associated with one another in the way that certain mental processes regularly correspond to certain physical processes or, figuratively expressed, run ‘parallel to one another’. Although the inner experience is based on the functions of the brain there are no physical causes for mental changes.” Leibniz wrote: “Souls act according to the laws of final causes, through aspirations, ends and means. Bodies act according to the laws of efficient causes, i.e., the laws of motion. And these two realms, that of efficient causes and that of final causes, harmonize with one another.” Wundt follows Leibniz and differentiates between a physical causality (natural causality of neurophysiology) and a mental causality (psychic) of the consciousness process. Both causalities, however, are not opposites in a dualistic metaphysical sense, but depend on the standpoint. Causal explanations in psychology must be content to seek the effects of the antecedent causes without being able to derive exact predictions. Using the example of volitional acts, Wundt describes possible inversion in considering cause and effect, ends and means, and explains how causal and teleological explanations can complement one another to establish a co-ordinated consideration. Wundt’s position differed from contemporary authors who also favoured parallelism. Instead of being content with the postulate of parallelism, he developed his principles of mental causality in contrast to the natural causality of neurophysiology, and a corresponding methodology. There are two fundamentally different approaches of the postulated psychophysical unit, not just two points- of-view in the sense of Gustav Theodor Fechner’s identity hypothesis. Psychological and physiological statements exist in two categorically different reference systems; the important categories are to be emphasised in order to prevent category mistakes as discussed by Nicolai Hartmann. In this regard, Wundt created the first genuine epistemology and methodology of empirical psychology (the term philosophy of science did not yet exist). CU IDOL SELF LEARNING MATERIAL (SLM)

Contribution of Weber, Fechner, Wundt and Galton 49 Apperception Apperception is Wundt’s central theoretical concept. Leibniz described apperception as the process in which the elementary sensory impressions pass into (self-) consciousness, whereby individual aspirations (striving, volitional acts) play an essential role. Wundt developed psychological concepts, used experimental psychological methods and put forward neuropsychological modelling in the frontal cortex of the brain system – in line with today’s thinking. Apperception exhibits a range of theoretical assumptions on the integrative process of consciousness. The selective control of attention is an elementary example of such active cognitive, emotional and motivational integration. Development Theory of the Mind The fundamental task is to work out a comprehensive development theory of the mind – from animal psychology to the highest cultural achievements in language, religion and ethics. Unlike other thinkers of his time, Wundt had no difficulty connecting the development concepts of the humanities (in the spirit of Friedrich Hegel and Johann Gottfried Herder) with the biological theory of evolution as expounded by Charles Darwin. Critical Realism Wundt determined that “psychology is an empirical science co-ordinating natural science and humanities, and that the considerations of both complement one another in the sense that only together can they create for us a potential empirical knowledge.” He claimed that his views were free of metaphysics and were based on certain epistemological presuppositions, including the differentiation of subject and object in the perception, and the principle of causality. With his term critical realism, Wundt distinguishes himself from other philosophical positions. Definition of Psychology Wundt set himself the task of redefining the broad field of psychology between philosophy and physiology, between the humanities and the natural sciences. In place of the metaphysical definition as a science of the soul came the definition, based on scientific theory, of empirical psychology as a psychology of consciousness with its own categories and epistemological principles. Psychology CU IDOL SELF LEARNING MATERIAL (SLM)

50 Experimental Psychology examines the “entire experience in its immediately subjective reality.” The task of psychology is to precisely analyse the processes of consciousness, to assess the complex connections (psychische Verbindungen), and to find the laws governing such relationships. 1. Psychology is not a science of the individual soul. Life is a uniform mental and physical process that can be considered in a variety of ways in order to recognise general principles, particularly the psychological-historical and biological principles of development. Wundt demanded an understanding of the emotional and the volitional functions, in addition to cognitive features, as equally important aspects of the unitary (whole) psychophysical process. 2. Psychology cannot be reduced to physiology. The tools of physiology remain fundamentally insufficient for the task of psychology. Such a project is meaningless “because the interrelations between mental processes would be incomprehensible even if the interrelations between brain processes were as clearly understood as the mechanism of a pocket watch.” 3. Psychology is concerned with conscious processes. Wundt rejected making subconscious mental processes a topic of scientific psychology for epistemological and methodological reasons. In his day there were, before Sigmund Freud, influential authors such as the philosopher Eduard von Hartmann (1901), who postulated a metaphysics of the unconscious. Wundt had two fundamental objections. He rejected all primarily metaphysically founded psychology and he saw no reliable methodological approach. He also soon revised his initial assumptions about unconscious judgements. When Wundt rejects the assumption of “the unconscious” he is also showing his scepticism regarding Fechner’s theory of the unconscious and Wundt is perhaps even more greatly influenced by the flood of writing at the time on hypnotism and spiritualism (Wundt, 1879, 1892). While Freud frequently quoted from Wundt’s work, Wundt remained sceptical about all hypotheses that operated with the concept of “the unconscious”. For Wundt, it would be just as much a misunderstanding to define psychology as a behavioural science in the sense of the later concept of strict behaviourism. Numerous behavioural and psychological variables had already been observed or measured at the Leipzig laboratory. CU IDOL SELF LEARNING MATERIAL (SLM)

Contribution of Weber, Fechner, Wundt and Galton 51 Wundt stressed that physiological effects, for example the physiological changes accompanying feelings, were only tools of psychology, as were the physical measurements of stimulus intensity in psychophysics. Further developing these methodological approaches one-sidedly would ultimately, however, lead to a behavioural physiology, i.e., a scientific reductionism, and not to a general psychology and cultural psychology. 4. Psychology is an empirical humanities science. Wundt was convinced of the triple status of psychology: (i) as a science of the direct experience, it contrasts with the natural sciences that refer to the indirect content of experience and abstract from the subject; (ii) as a science “of generally valid forms of direct human experience it is the foundation of the humanities”; (iii) among all the empirical sciences, it was “the one whose results most benefit the examination of the general problems of epistemology and ethics – the two fundamental areas of philosophy.” Wundt’s concepts were developed during almost 60 years of research and teaching that led him from neurophysiology to psychology and philosophy. The interrelationships between physiology, philosophy, logic, epistemology and ethics are therefore essential for an understanding of Wundt’s psychology. The core of Wundt’s areas of interest and guiding ideas can already be seen in his Vorlesungen über die Menschen-und Tierseele (Lectures on Human and Animal Psychology) of 1863: individual psychology (now known as general psychology, i.e., areas such as perception, attention, apperception, volition, will, feelings and emotions); cultural psychology (Wundt’s Völkerpsychologie) as development theory of the human mind); animal psychology; and neuropsychology. The initial conceptual outlines of the 30-year-old Wundt (1862, 1863) led to a long research program, to the founding of the first Institute and to the treatment of psychology as a discipline, as well as to a range of fundamental textbooks and numerous other publications. CU IDOL SELF LEARNING MATERIAL (SLM)

52 Experimental Psychology Tridimensional Theory of Feeling The theory that feelings can vary along three dimensions: pleasantness-unpleasantness (hedonic quality), excitement-calmness, and arousal-relaxation. The tridimensional theory is used to define different emotions as characterized by different combinations and successions of feelings and by the specific course of change of the feelings along each of the three dimensions. excitement pleasure relaxation strain displeasure calm Fig. 2.4: Tridimensional Theory of Feeling A structuralism reconstruction of Wilhelm Wundt’s three-dimensional theory of emotion and a sketch of its theoretical environment are presented. Wundt’s theory, a quantitative theory of the structure of emotional experience, is reconstructed as a small theory-net consisting of the basic theory-element TE(WUNDT) and several specializations. The main substantive axiom of TE(WUNDT) postulates that each emotional quality, unless itself basic, results from the fusion of a characteristic “mixture” of six basic forms of feeling: Pleasure, displeasure, excitement, inhibition (tranquillization), tension, and relaxation. A second axiom holds that these basic feeling qualities are organized into three “bipolar” dimensions; and the third axiom claims that the basic emotions experienced with regard to complex objects are a fusion of the corresponding basic feelings directed at the components of the complex objects. The constraint of the theory holds that the mixtures of CU IDOL SELF LEARNING MATERIAL (SLM)

Contribution of Weber, Fechner, Wundt and Galton 53 basic feelings characteristic for the various non-basic emotions are the same across different admissible models. Specializations of the theory result from different possible specifications of the central fusion axiom, as well as from additional constraints requiring constancy of the emotional reactions to some kinds of objects. 2.7 Contribution of Wundt Wilhelm Wundt opened the Institute for Experimental Psychology at the University of Leipzig in Germany in 1879. This was the first laboratory dedicated to psychology, and its opening is usually thought of as the beginning of modern psychology. Indeed, Wundt is often regarded as the father of psychology. Wundt was important because he separated psychology from philosophy by analyzing the workings of the mind in a more structured way, with the emphasis being on objective measurement and control. This laboratory became a focus for those with a serious interest in psychology, first for German philosophers and psychology students, then for American and British students as well. All subsequent psychological laboratories were closely modeled in their early years on the Wundt model. Wundt’s background was in physiology, and this was reflected in the topics with which the Institute was concerned, such as the study of reaction times and sensory processes and attention. For example, participants would be exposed to a standard stimulus (e.g., a light or the sound of a metronome) and asked to report their sensations. Wundt’s aim was to record thoughts and sensations, and to analyze them into their constituent elements, in much the same way as a chemist analyses chemical compounds, in order to get at the underlying structure. The school of psychology founded by Wundt is known as voluntarism, the process of organizing the mind. During his academic career, Wundt trained 186 graduate students (116 in psychology). This is significant as it helped disseminate his work. Indeed, parts of Wundt’s theory were developed and promoted by his one-time student, Edward Titchener, who described his system as Structuralism, or the analysis of the basic elements that constitute the mind. CU IDOL SELF LEARNING MATERIAL (SLM)

54 Experimental Psychology Wundt wanted to study the structure of the human mind (using introspection). Wundt believed in reductionism, i.e., he believed consciousness could be broken down (or reduced) to its basic elements without sacrificing any of the properties of the whole. Wundt argued that conscious mental states could be scientifically studied using introspection. Wundt’s introspection was not a causal affair, but a highly practiced form of self-examination. He trained psychology students to make observations that were biased by personal interpretation or previous experience, and used the results to develop a theory of conscious thought. Highly trained assistants would be given a stimulus such as a ticking metronome and would reflect on the experience. They would report what the stimulus made them think and feel. The same stimulus, physical surroundings and instructions were given to each person. Wundt’s method of introspection did not remain a fundamental tool of psychological experimentation past the early 1920s. His greatest contribution was to show that psychology could be a valid experimental science. Therefore, one way Wundt contributed to the development of psychology was to do his research in carefully controlled conditions, i.e., experimental methods. This encouraged other researchers such as the behaviorists to follow the same experimental approach and be more scientific. However, today psychologists (e.g., Skinner) argue that introspection was not really scientific even if the methods used to introspect were. Skinner claims the results of introspection are subjective and cannot be verified because only observable behavior can be objectively measured. Wundt concentrated on three areas of mental functioning; thoughts, images and feelings. These are the basic areas studied today in cognitive psychology. This means that the study of perceptual processes can be traced back to Wundt. Wundt’s work stimulated interest in cognitive psychology. On the basis of his work, and the influence it had on psychologists who were to follow him, Wundt can be regarded as the founder of experimental psychology, so securing his place in the history of psychology. At the same time, Wundt himself believed that the experimental approach was limited in scope, and that other methods would be necessary if all aspects of human psychology were to be investigated. CU IDOL SELF LEARNING MATERIAL (SLM)

Contribution of Weber, Fechner, Wundt and Galton 55 2.8 Sir Francis Galton Sir Francis Galton, FRS was an English Victorian era statistician, polymath, sociologist, psychologist, anthropologist, eugenicist, tropical explorer, geographer, inventor, meteorologist, proto- geneticist, and psychometrician. He was knighted in 1909. Galton produced over 340 papers and books. He also created the statistical concept of correlation and widely promoted regression toward the mean. He was the first to apply statistical methods to the study of human differences and inheritance of intelligence, and introduced the use of questionnaires and surveys for collecting data on human communities, which he needed for genealogical and biographical works and for his anthropometric studies. Fig. 2.5: Sir Francis Galton As an investigator of the human mind, he founded psychometrics (the science of measuring mental faculties) and differential psychology and the lexical hypothesis of personality. He devised a method for classifying fingerprints that proved useful in forensic science. He also conducted research CU IDOL SELF LEARNING MATERIAL (SLM)

56 Experimental Psychology on the power of prayer, concluding it had none by its null effects on the longevity of those prayed for. His quest for the scientific principles of diverse phenomena extended even to the optimal method for making tea. As the initiator of scientific meteorology, he devised the first weather map, proposed a theory of anticyclones, and was the first to establish a complete record of short-term climatic phenomena on a European scale. He also invented the Galton Whistle for testing differential hearing ability. He was Charles Darwin’s half-cousin. Early Life Galton was born at “The Larches”, a large house in the Sparkbrook area of Birmingham, England, built on the site of “Fair Hill”, the former home of Joseph Priestley, which the botanist William Withering had renamed. He was Charles Darwin’s half-cousin, sharing the common grandparent Erasmus Darwin. His father was Samuel Tertius Galton, son of Samuel “John” Galton. The Galtons were Quaker gun-manufacturers and bankers, while the Darwins were involved in medicine and science. He was cousin of Douglas Strutt Galton and half-cousin of Charles Darwin. Both families had Fellows of the Royal Society and members who loved to invent in their spare time. Both Erasmus Darwin and Samuel Galton were founding members of the Lunar Society of Birmingham, which included Boulton, Watt, Wedgwood, Priestley and Edgeworth. Both families were known for their literary talent. Erasmus Darwin composed lengthy technical treatises in verse. Galton’s aunt Mary Anne Galton wrote on aesthetics and religion, and her autobiography detailed the environment of her childhood populated by Lunar Society members. Galton was a child prodigy – he was reading by the age of two; at age five he knew some Greek, Latin and long division, and by the age of six, he had moved on to adult books, including Shakespeare for pleasure and poetry, which he quoted at length. Later in life, Galton proposed a connection between genius and insanity based on his own experience: Men who leave their mark on the world are very often those who, being gifted and full of nervous power, are at the same time haunted and driven by a dominant idea, and are therefore within a measurable distance of insanity. According to the records of the United Grand Lodge of England, it was in February 1844 that Galton became a freemason at the Scientific lodge, held at the Red Lion Inn in Cambridge, progressing CU IDOL SELF LEARNING MATERIAL (SLM)

Contribution of Weber, Fechner, Wundt and Galton 57 through the three masonic degrees: Apprentice, 5 February 1844; Fellow Craft, 11 March 1844; Master Mason, 13 May 1844. A note in the record states: “Francis Galton Trinity College student, gained his certificate 13 March 1845”. One of Galton’s masonic certificates from Scientific lodge can be found among his papers at University College, London. A nervous breakdown prevented Galton’s intent to try for honours. He elected instead to take a “poll” (pass) B.A. degree, like his half-cousin Charles Darwin. (Following the Cambridge custom, he was awarded an M.A. without further study, in 1847.) He briefly resumed his medical studies but the death of his father in 1844 left him emotionally destitute, though financially independent, and he terminated his medical studies entirely, turning to foreign travel, sport and technical invention. In his early years, Galton was an enthusiastic traveller, and made a notable solo trip through Eastern Europe to Constantinople, before going up to Cambridge. In 1845 and 1846, he went to Egypt and travelled up the Nile to Khartoum in the Sudan, and from there to Beirut, Damascus and down the Jordan. In 1850, he joined the Royal Geographical Society, and over the next two years mounted a long and difficult expedition into then little-known South West Africa (now Namibia). He wrote a book on his experience, “Narrative of an Explorer in Tropical South Africa”. He was awarded the Royal Geographical Society’s Founder’s Gold Medal in 1853 and the Silver Medal of the French Geographical Society for his pioneering cartographic survey of the region. This established his reputation as a geographer and explorer. He proceeded to write the best-selling The Art of Travel, a handbook of practical advice for the Victorian on the move, which went through many editions and is still in print. Middle Years Galton was a polymath who made important contributions in many fields of science, including meteorology (the anti-cyclone and the first popular weather maps), statistics (regression and correlation), psychology (synaesthesia), biology (the nature and mechanism of heredity), and criminology (fingerprints). Much of this was influenced by his penchant for counting or measuring. Galton prepared the first weather map published in The Times (1 April 1875, showing the weather from the previous day, 31 March), now a standard feature in newspapers worldwide. CU IDOL SELF LEARNING MATERIAL (SLM)

58 Experimental Psychology He became very active in the British Association for the Advancement of Science, presenting many papers on a wide variety of topics at its meetings from 1858 to 1899. He was the General Secretary from 1863 to 1867, President of the Geographical section in 1867 and 1872, and President of the Anthropological Section in 1877 and 1885. He was active on the Council of the Royal Geographical Society for over forty years, in various committees of the Royal Society, and on the Meteorological Council. James McKeen Cattell, a student of Wilhelm Wundt who had been reading Galton’s articles, decided he wanted to study under him. He eventually built a professional relationship with Galton, measuring subjects and working together on research. In 1888, Galton established a lab in the science galleries of the South Kensington Museum. In Galton’s lab, participants could be measured to gain knowledge of their strengths and weaknesses. Galton also used these data for his own research. He would typically charge people a small fee for his services. In 1873, Galton wrote a controversial letter to The Times titled ‘Africa for the Chinese’, where he argued that the Chinese, as a race capable of high civilization and only temporarily stunted by the recent failures of Chinese dynasties, should be encouraged to immigrate to Africa and displace the supposedly inferior aboriginal blacks. Galton in His Later Years The publication by his cousin Charles Darwin of The Origin of Species in 1859 was an event that changed Galton’s life. He came to be gripped by the work, especially the first chapter on “Variation under Domestication”, concerning animal breeding. Galton devoted much of the rest of his life to exploring variation in human populations and its implications, at which Darwin had only hinted. In doing so, he established a research program which embraced multiple aspects of human variation, from mental characteristics to height; from facial images to fingerprint patterns. This required inventing novel measures of traits, devising large-scale collection of data using those measures, and in the end, the discovery of new statistical techniques for describing and understanding the data. CU IDOL SELF LEARNING MATERIAL (SLM)

Contribution of Weber, Fechner, Wundt and Galton 59 Galton was interested at first in the question of whether human ability was hereditary, and proposed to count the number of the relatives of various degrees of eminent men. If the qualities were hereditary, he reasoned, there should be more eminent men among the relatives than among the general population. To test this, he invented the methods of historiometry. Galton obtained extensive data from a broad range of biographical sources which he tabulated and compared in various ways. This pioneering work was described in detail in his book Hereditary Genius in 1869. Here, he showed, among other things, that the numbers of eminent relatives dropped off when going from the first degree to the second degree relatives, and from the second degree to the third. He took this as evidence of the inheritance of abilities. Galton recognized the limitations of his methods in these two works, and believed the question could be better studied by comparisons of twins. His method envisaged testing to see if twins who were similar at birth diverged in dissimilar environments, and whether twins dissimilar at birth converged when reared in similar environments. He again used the method of questionnaires to gather various sorts of data, which were tabulated and described in a paper The History of Twins in 1875. In so doing, he anticipated the modern field of behaviour genetics, which relies heavily on twin studies. He concluded that the evidence favoured nature rather than nurture. He also proposed adoption studies, including trans-racial adoption studies, to separate the effects of heredity and environment. Galton recognized that cultural circumstances influenced the capability of a civilization’s citizens, and their reproductive success. In Hereditary Genius, he envisaged a situation conducive to resilient and enduring civilization as follows: The best form of civilization in respect to the improvement of the race, would be one in which society was not costly; where incomes were chiefly derived from professional sources, and not much through inheritance; where every lad had a chance of showing his abilities, and, if highly gifted, was enabled to achieve a first-class education and entrance into professional life, by the liberal help of the exhibitions and scholarships which he had gained in his early youth; where marriage was held in as high honour as in ancient Jewish times; where the pride of race was encouraged (of course I do not refer to the nonsensical sentiment of the present day, that goes under that name); where the weak could find a welcome and a refuge in celibate monasteries or sisterhoods, and lastly, CU IDOL SELF LEARNING MATERIAL (SLM)

60 Experimental Psychology where the better sort of emigrants and refugees from other lands were invited and welcomed, and their descendants naturalized. Sir Francis Galton, 1890s Galton’s formulation of regression and its link to the bivariate normal distribution can be traced to his attempts at developing a mathematical model for population stability. Although Galton’s first attempt to study Darwinian questions, Hereditary Genius, generated little enthusiasm at the time, the text led to his further studies in the 1870s concerning the inheritance of physical traits. This text contains some crude notions of the concept of regression, described in a qualitative matter. For example, he wrote of dogs: “If a man breeds from strong, well-shaped dogs, but of mixed pedigree, the puppies will be sometimes, but rarely, the equals of their parents. They will commonly be of a mongrel, non-descript type, because ancestral peculiarities are apt to crop out in the offspring.” This notion created a problem for Galton, as he could not reconcile the tendency of a population to maintain a normal distribution of traits from generation to generation with the notion of inheritance. It seemed that a large number of factors operated independently on offspring, leading to the normal distribution of a trait in each generation. However, this provided no explanation as to how a parent can have a significant impact on his offspring, which was the basis of inheritance. Galton’s development of the law of regression to the mean, or reversion, was due to insights from the quincunx (‘bean machine’) and his studies of sweet peas. While Galton had previously invented the quincunx prior to February 1874, the 1877 version of the quincunx had a new feature that helped Galton demonstrate that a normal mixture of normal distributions is also normal. Galton demonstrated this using a new version of quincunx, adding chutes to the apparatus to represent reversion. When the pellets passed through the curved chutes (representing reversion) and then the pins (representing family variability), the result was a stable population. On Friday 19 February 1877, Galton gave a lecture entitled Typical Laws of Heredity at the Royal Institution in London. In this lecture, he posed that there must a counteracting force to maintain population stability. However, this model required a much larger degree of intergenerational natural selection than was plausible. In 1875, Galton started growing sweet peas and addressed the Royal Institution on his findings on 9 February 1877. He found that each group of progeny seeds followed a normal curve, and the CU IDOL SELF LEARNING MATERIAL (SLM)

Contribution of Weber, Fechner, Wundt and Galton 61 curves were equally disperse. Each group was not centered about the parent’s weight, but rather at a weight closer to the population average. Galton called this reversion, as every progeny group was distributed at a value that was closer to the population average than the parent. The deviation from the population average was in the same direction, but the magnitude of the deviation was only one- third as large. In doing so, Galton demonstrated that there was variability among each of the families, yet the families combined to produce a stable, normally distributed population. When Galton addressed the British Association for the Advancement of Science in 1885, he said of his investigation of sweet peas, “I was then blind to what I now perceive to be the simple explanation of the phenomenon.” Galton was able to further his notion of regression by collecting and analyzing data on human stature. Galton asked for help of mathematician J. Hamilton Dickson in investigating the geometric relationship of the data. He determined that the regression coefficient did not ensure population stability by chance, but rather that the regression coefficient, conditional variance, and population were interdependent quantities related by a simple equation. Thus Galton identified that the linearity of regression was not coincidental but rather was a necessary consequence of population stability. The model for population stability resulted in Galton’s formulation of the Law of Ancestral Heredity. This law, which was published in Natural Inheritance, states that the two parents of an offspring jointly contribute one half of an offspring’s heritage, while the other, more-removed ancestors constitute a smaller proportion of the offspring’s heritage. Galton viewed reversion as a spring, that when stretched, would return the distribution of traits back to the normal distribution. He concluded that evolution would have to occur via discontinuous steps, as reversion would neutralize any incremental steps. When Mendel’s principles were rediscovered in 1900, this resulted in a fierce battle between the followers of Galton’s Law of Ancestral Heredity, the biometricians, and those who advocated Mendel’s principles. Empirical Test of Pangenesis and Lamarckism Galton conducted wide-ranging inquiries into heredity which led him to challenge Charles Darwin’s hypothesis of pangenesis. Darwin had proposed as part of this model that certain particles, which he called “gemmules” moved throughout the body and were also responsible for the inheritance of acquired characteristics. Galton, in consultation with Darwin, set out to see if they were transported in the blood. In a long series of experiments in 1869 to 1871, he transfused the blood between CU IDOL SELF LEARNING MATERIAL (SLM)

62 Experimental Psychology dissimilar breeds of rabbits, and examined the features of their offspring. He found no evidence of characters transmitted in the transfused blood. 2.9 Contribution of Galton Galton was one of the first experimental psychologists, and the founder of the field of enquiry now called Differential Psychology, which concerns itself with psychological differences between people, rather than on common traits. He started virtually from scratch, and had to invent the major tools he required, right down to the statistical methods – correlation and regression – which he later developed. These are now the nuts-and-bolts of the empirical human sciences, but were unknown in his time. One of the principal obstacles he had to overcome was the treatment of differences on measures as measurement error, rather than as natural variability. His influential study Hereditary Genius (1869) was the first systematic attempt to investigate the effect of heredity on intellectual abilities, and was notable for its use of the bell-shaped Normal Distribution, then called the “Law of Errors”, to describe differences in intellectual ability, and its use of pedigree analysis to determine hereditary effects. Later Galton went on to suggest the use of twin studies to disentangle nature from nurture, by comparing identical twins to fraternal twins. The research program that Galton initiated in this regard has developed into the important field of behaviour genetics. Galton later broadened his study of human traits into general anthropometry, or “measurement of man”, trying to find as many measurable traits as possible, so that their distribution and heritability could be determined. His psychological studies also embraced mental differences in visualization, and he was the first to identify and study “number forms”, now called “synaesthesia”. He also invented the word- association test, and investigated the operations of the subconscious mind. His work in this area was collected into a wide-ranging volume called Inquiries into Human Faculty, which must be read today, with Galton’s broader research program in mind: to identify and measure variable human traits. CU IDOL SELF LEARNING MATERIAL (SLM)

Contribution of Weber, Fechner, Wundt and Galton 63 In 1873, the Swiss botanist Alphonse de Candolle published a refutation of Galton’s Hereditary Genius, arguing that environmental factors played a much greater part in the creation of eminence than Galton had claimed. In response, Galton devised and distributed one of the first early – and very large – psychological questionnaires to nearly two hundred members of the Royal Society, including questions on the development of their scientific ability, their religious inclinations and assessment of their own characters. In 1874, Galton published the results in Englishmen of Science: Their Nature and Nurture, coining the expressions for innate and environmental influences that have characterised the debate ever since. Although Galton considered this work an entirely objective account, many of the questions were designed – either consciously or unconsciously – to elicit particular responses, and his interpretation of the results had a tendency to fit them to his own preconceptions. In spite of the obvious flaws, this was a pioneering piece of work, which led the way in the development of one of the key tools of psychological research. The resultant work also illustrated that Galton would at least allow that environmental factors (or ‘nurture’) played some role in the development of a person: ‘the effects of education and circumstances are so interwoven with those of natural character in determining a man’s position among his contemporaries, that I find it impossible to treat them wholly apart’. Work on this volume also awoke Galton to the value of identical twins for teasing out the effects on an individual of ‘education and circumstances’ from ‘natural character’. Galton was thwarted in his hopes to find numerous sets of twins who had been separated at birth so that he could clearly differentiate between innate and environmental factors. This approach is one that has been developed so that twin studies in particular the comparison of identical and non-identical twins – have contributed much to our understanding of human heredity. Later, Galton explored ways to measure psychological differences between individuals, creating a new discipline in experimental psychology. His new technique employed introspection and self- analysis ‘allowing the mind to play freely…until a couple…of ideas have passed through it, and then…to turn the attention upon them with a sudden and complete reawakening’. He realized that surprising links might be found, and that beneath the level of day-to-day conscious experience lay a more complex world. Galton conceived a word-association experiment to explore this world, and CU IDOL SELF LEARNING MATERIAL (SLM)

64 Experimental Psychology tested it on himself, realising that many of the associations he made were related to his youth. These experiments preceded by many years Freud’s work attempting to reveal and understand the subconscious. To test the abilities of others, he started with another questionnaire in 1879 – Questions on the Faculty of Visualising – designed to test visual recall and starting with how well participants could recall their morning breakfast table, then moving on to more general ability to visualise people. He found, to his astonishment, that scientists generally performed poorly at these tasks; and people in general were enormously variable. This work was ground-breaking and laid the template for future studies of mental imagery. Galton also discovered that people showed vast differences in the way they perceived numbers, each being highly personalised to the individuals. He further found synaesthesia in some people, who associated different numbers, letters or words with the sensation of colour. He published all these findings in Inquiries into Human Faculty in 1883. It was in this work that he introduced the word eugenics. Statistics and Anthropometrics In the mid-nineteenth century, there were few ways of analysing statistical data. In 1846, the Belgian statistician Quetelet demonstrated that human measurements such as the heights of French conscripts approximated to a normal distribution, or a bell curve. Galton wondered if this could be applied to human ability, and in the absence of any independent measure analyzed the results of the admission exam to the Royal Military Academy at Sandhurst, which he found approximated to a normal distribution. On the basis of this, he divided intelligence into fourteen classes; at the top end of the curve were the subjects of Hereditary Genius and at the lower end ‘idiots and imbeciles’. In 1884, Galton was given an unprecedented opportunity to indulge his enthusiasm for the measurement of man, or anthropometry. As he said during the delivery of the Rede Lecture at The University of Cambridge in May of that year: ‘The powers of man are finite, and if finite are not too large for measurement’. The International Health Exhibition, held in London in 1884 was the occasion of the launch of Galton’s first anthropometric laboratory; participants paid an entry fee of three CU IDOL SELF LEARNING MATERIAL (SLM)

Contribution of Weber, Fechner, Wundt and Galton 65 pence to undergo a series of tests, including height, weight, strength, breathing capacity, reaction time, hearing and vision, colour perception and judgement of length. Galton had to exercise his flair for invention as he had to design some of the instruments himself. By 1885 when the exhibition closed, Galton had measured 10000 individuals with over 150,000 separate measurements. Galton kept all the results for his records, while the subjects went away with copies of their individual results. At a time when modern statistics was a developing mathematical science, the challenge to analysis this enormous set of data was immense. Galton also wanted to examine the way that traits such as height were inherited, and he was able to do this with data from 205 sets of parents and their adult children. Plotting the data he found the expected positive association between the heights of the parents and children. However, although very tall parents tended to have tall children, he found that the children tended to be shorter than their parents. Similarly, if parents were short, their children were slightly taller. These data reflected experiments of 1876 with the seeds of sweet peas; using seven groups of seeds, he measured the average diameter of 100 seeds produced by each sweet pea plant. He founded that the smallest pea seeds had larger offspring and the largest seeds had smaller offspring. Galton had discovered the phenomenon of ‘regression to the mean’, where the largest peas and parents had offspring who were smaller and closer to the mean. From this work, Galton derived the so-called regression coefficient, and later, for association between any two variables, the correlation coefficient. This would pave the way for the development of statistics as a discipline, through Galton’s follower Karl Pearson and marked the beginning of a new phase of scientific investigation that allowed the objective examination of enormously complex data resulting from biological, psychological and social phenomena. Unfortunately, Galton was unable to see that his great discovery had undermined his eugenic ideals, which proposed a more straightforward relationship between traits such as height and intelligence in parents and their children. In 1886, Galton was awarded the Gold Medal from the Royal Society for his work on statistics applied to biology. This recognized not only his work on regression and correlation, but also his quantitative approach to all the fields that lent themselves to measurement and statistical analysis. CU IDOL SELF LEARNING MATERIAL (SLM)

66 Experimental Psychology Galton gave in to his predilection for counting at every opportunity; whilst at Vichy in France, he spent a few hours classifying women into six size categories; from ‘thin’ to ‘prize fat’. This gave way to his project to define a beauty map of Great Britain; to record his observations of women as ‘attractive’, ‘indifferent’ or ‘repellent’. He secreted a piece of card and a ‘pricker’ fixed on a glove which he kept in his pocket, and used the needle to make a mark at one end to signify an ‘attractive’ girl, in the middle for an ‘indifferent’ girl, and at the other end for the unfortunate ‘repellents’. He could later read off and count the results at leisure. He found ‘London to rank highest for beauty, Aberdeen lowest’, showing again that he was blindly unaware of how his prejudices coloured his observations. Criminology and Fingerprints Galton’s desire to quantify knew no bounds, and the experiment of the anthropometric laboratory led him to consider how measurement could be used for identification of individuals, particularly in relation to policing and detection of criminals. Galton joined in a project to examine the faces of British criminals to ascertain if ‘consummate scoundrels’ could be identified by special criminal characteristics. He started by creating ‘composites’ by exposing a number of images of different criminals onto a single photographic plate. The effect of this was to create an ‘average’ face, which did the opposite of what was expected, resulting in a very ordinary looking person. But there were other avenues to explore: a French policeman, Alphonse Bertillon, developed a system to measure a number of specific physical dimensions (e.g., hands, feet, head) which could be catalogued in such a way to simplify searching for similar types. The individual profile included full-on and side-on mug- shots, which, for Galton, who believed that the psychological character manifested in physical features, were of immense interest. Galton recognized that this profiling could be combined with fingerprinting to make a real contribution to the detection of criminals. William Herschel, a civil servant in India, had used hand and fingerprints to identify individuals in his area of administration. Henry Faulds, a missionary who had lived in Japan where fingerprinting had been used for centuries, had spent some time in the CU IDOL SELF LEARNING MATERIAL (SLM)

Contribution of Weber, Fechner, Wundt and Galton 67 1880s trying to convince Scotland Yard to use the technique in policing. Galton was enthusiastic about the potential of this technique, but he realised that, in order to be accepted by the policing authorities, he needed to establish that: (a) fingerprints do not change through adult life; (b) the variety is extremely great, and (c) they can be classified. He spent many years in the 1880s and 1890s, starting with Faulds’ classification system, examining large numbers of fingerprints to establish their unique attributes. He further looked at fingerprints from the same person but separated by decades to pronounce that they were unchanging over time. Classification proved more challenging, but Galton used the major characters of each fingerprint (arch (A), loop (L) or whorl (W)) to come up with a series of ten letters (one for each finger/thumb) that could contribute to Bertillon’s filing system. Gallon published his systematic study in 1892, entitled Finger Prints. This work eventually contributed to an appraisal of the options and the adoption of fingerprinting and Bertillon’s indexing system in criminology. Galton got all the acclaim, giving some of the credit to Herschel, but Henry Faulds, who had tried unsuccessfully to convince the police authorities of the value of fingerprinting a decade earlier, was ignored. 2.10 Summary Ernst Weber was a German physiologist and psychologist. He was regarded as a predecessor of experimental psychology and one of the founders of Psychophysics, the branch of psychology that studies the relations between physical stimuli and mental states. He is known chiefly for his work on investigation of subjective sensory response (sensations) to the impact of external physical stimuli: weight, temperature and pressure. Weber experimentally determined the accuracy of tactile sensations, namely, the distance between two points on the skin, in which a person can perceive two separate touches. He discovered the two-point threshold the distance on the skin separating two pointed stimulators that is required to experience two rather than one point of stimulation. Weber was the first to draw the attention of physiologists to the skin as the seat of differentiated sense organs directed toward the external world, like other sensory organs, in contrast with the common sensibility directed toward our own body. His research had many philosophical implications and a great impact on further studies of skin senses and some general problems of sensation by CU IDOL SELF LEARNING MATERIAL (SLM)

68 Experimental Psychology physiologists and psychologists. He began a very fruitful period in the research on senses and is rightly considered as one of the founders of psychophysics. His work on tactile sensations has become classic. Gustav Theodor Fechner was a German philosopher, physicist and experimental psychologist. An early pioneer in experimental psychology and founder of psychophysics, he inspired many 20th- century scientists and philosophers. In 1834, he was appointed professor of physics at Leipzig. But in 1839, he contracted an eye disorder while studying the phenomena of color and vision, and, after much suffering, resigned. Subsequently, recovering, he turned to the study of the mind and its relations with the body, giving public lectures on the subjects dealt with in his books. Whilst lying in bed, Fechner had an insight into the relationship between mental sensations and material sensations. This insight proved to be significant in the development of psychology as there was now a quantitative relationship between the mental and physical worlds. Gustav Theodor Fechner was born on 19 April 1801, at Gross-Särchen, Lower Lusatia. He earned his degree in Biological Science in 1822 at the University of Leipzig and taught there until his death on 18 November 1887. Having developed an interest in Mathematics and Physics, he was appointed Professor of Physics in 1834. Fechner believed that everything is endowed with a soul; nothing is without a material basis; mind and matter are the same essence, but seen from different sides. Moreover, he believed that, by means of psychophysical experiments in psychology, the foregoing assertions were demonstrated and proved. He authored many books and monographs on such diverse subjects as medicine, esthetics, and experimental psychology, affixing the pseudonym Dr. Mises to some of them. The ultimate philosophic problem which concerned Fechner, and to which his psychophysics was a solution, was the perennial mind-body problem. His solution has been called the identity hypothesis: mind and body are not regarded as a real dualism, but are different sides of one reality. They are separated in the form of sensation and stimulus, i.e., what appears from a subjective viewpoint as the mind, appears from an external or objective viewpoint as the body. In the expression of the equation of Fechner’s law (sensation intensity = C log stimulus intensity), it becomes evident CU IDOL SELF LEARNING MATERIAL (SLM)

Contribution of Weber, Fechner, Wundt and Galton 69 that the dualism is not real. While this law has been criticized as illogical, and for not having universal applicability, it has been useful in research on hearing and vision. Wilhelm Maximilian Wundt was a physician, physiologist, philosopher and professor, known today as one of the founders of modern psychology. Wundt, who distinguished psychology as a science from philosophy and biology, was the first person ever to call himself a psychologist. He is widely regarded as the “Father of Experimental Psychology”. In 1879, at University of Leipzig, Wundt founded the first formal laboratory for psychological research. This marked psychology as an independent field of study. Psychology is interested in the current process, i.e., the mental changes and functional relationships between perception, cognition, emotion, and volition/ motivation. Mental (psychological) phenomena are changing processes of consciousness. They can only be determined as an actuality, an “immediate reality of an event in the psychological experience”. The relationships of consciousness, i.e., the actively organising processes, are no longer explained metaphysically by means of an immortal ‘soul’ or an abstract transcendental (spiritual) principle. Influenced by Leibniz, Wundt introduced the term psychophysical parallelism as follows: “wherever there are regular relationships between mental and physical phenomena the two are neither identical nor convertible into one another because they are per se incomparable; but they are associated with one another in the way that certain mental processes regularly correspond to certain physical processes or, figuratively expressed, run ‘parallel to one another’. Although the inner experience is based on the functions of the brain there are no physical causes for mental changes.” Galton produced over 340 papers and books. He also created the statistical concept of correlation and widely promoted regression toward the mean. He was the first to apply statistical methods to the study of human differences and inheritance of intelligence, and introduced the use of questionnaires and surveys for collecting data on human communities, which he needed for genealogical and biographical works and for his anthropometric studies. Galton was a child prodigy he was reading by the age of two; at age five he knew some Greek, Latin and long division, and by the age of six he had moved on to adult books, including Shakespeare for pleasure, and poetry, which he quoted at length. Later in life, Galton proposed a connection between genius and insanity based on his own experience: CU IDOL SELF LEARNING MATERIAL (SLM)

70 Experimental Psychology Men who leave their mark on the world are very often those who, being gifted and full of nervous power, are at the same time haunted and driven by a dominant idea, and are therefore within a measurable distance of insanity. To test the abilities of others, he started with another questionnaire in 1879 – Questions on the Faculty of Visualising – designed to test visual recall and starting with how well participants could recall their morning breakfast table, then moving on to more general ability to visualise people. He found, to his astonishment, that scientists generally performed poorly at these tasks; and people in general were enormously variable. This work was ground-breaking and laid the template for future studies of mental imagery. Galton also discovered that people showed vast differences in the way they perceived numbers, each being highly personalised to the individuals. 2.11 Key Words/Abbreviations  Modern Experimental Psychology: Began with the adoption of experimental methods at the end of 19th century.  Physical Stimuli: In physiology, a stimulus is a detectable change. 2.12 Learning Activity 1. You are suggested to list out the contributions of Ernst Heinrich Weber and their practical applications. _________________________________________________________________ _________________________________________________________________ 2. You are required to prepare the report on “Contribution of Fechner for Experimental psychology”. _________________________________________________________________ _________________________________________________________________ CU IDOL SELF LEARNING MATERIAL (SLM)

Contribution of Weber, Fechner, Wundt and Galton 71 2.13 Unit End Exercises (MCQs and Descriptive) A. Descriptive Type Questions 1. Give the biography of Ernst Heinrich Weber. 2. Discuss the contribution of Ernst Heinrich Weber towards Experimental Psychology. 3. Discuss the biography of Gustav Theodor Fechner. 4. Explain the contribution of Fechner. 5. Discuss about contributions of Wilhelm Wundt. 6. Explain the contributions of Sir Francis Galton. B. Multiple Choice Questions 1. Weber’s law historically important psychological law quantifying the perception of change in a given __________. (a) Stimulus (b) Work Stress (c) Motivation (d) All the above 2. Who is the German anatomist and physiologist whose fundamental studies of the sense of touch introduced a concept that of the just noticeable difference? (a) Ernst Heinrich Weber (b) Gustav Theodor Fechner (c) Fechner (d) Wundt and Galton 3. Who is the German experimental psychologist who founded psychophysics and formulated Fechner’s law? (a) Ernst Heinrich Weber (b) Gustav Theodor Fechner (c) Fechner (d) Wundt and Galton CU IDOL SELF LEARNING MATERIAL (SLM)

72 Experimental Psychology 4. Who were a physician, physiologist, philosopher and professor, known today as one of the founders of modern psychology? (a) Ernst Heinrich Weber (b) Gustav Theodor Fechner (c) Fechner (d) Wilhelm Maximilian Wundt 5. Portrait of Galton by Octavius Oakley in the year __________. (a) 1840 (b) 1845 (c) 1880 (d) 1921 Answers: 1. (a), 2. (a), 3. (b), 4. (d), 5. (a) 2.14 References References of this unit have been given at the end of the book.  CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 73 UNIT 3 SENSORY PROCESSES: STRUCTURE AND FUNCTION OF EYE AND EAR Structure: 3.0 Learning Objectives 3.1 Introduction 3.2 Meaning of Sensory Processes 3.3 The Concept of Sensation 3.4 Structure of Sensory Processes 3.5 Structure and Function of Eye 3.6 Structure and Function of Ear 3.7 Summary 3.8 Key Words/Abbreviations 3.9 LearningActivity 3.10 Unit End Exercises (MCQs and Descriptive) 3.11 References 3.0 Learning Objectives After studying this unit, you will be able to:  Elaborate sensory processes of eye and ear  Explain the structure of sensory processes CU IDOL SELF LEARNING MATERIAL (SLM)

74 Experimental Psychology 3.1 Introduction The main sensory organ of the visual system is the eye, which takes in the physical stimuli of light rays and transduces them into electrical and chemical signals that can be interpreted by the brain to construct physical images. The eye has three main layers: the sclera, which includes the cornea; the choroid, which includes the pupil, iris and lens; and the retina, which includes receptor cells called rods and cones. The human visual system is capable of complex color perception, which is initiated by cones in the retina and completed by impulse integration in the brain. Depth perception is our ability to see in three dimensions and relies on both binocular (two-eye) and monocular (one- eye) cues. 3.2 Meaning of Sensory Processes Sensory processing is the process that organizes sensation from one’s own body and the environment, thus making it possible to use the body effectively within the environment. Description Sensory processing deals with how the brain processes multiple sensory modality inputs, such as proprioception, vision, auditory system, tactile, olfactory, vestibular system, interception, and taste into usable functional outputs. It has been believed for some time that inputs from different sensory organs are processed in different areas in the brain. The communication within and among these specialized areas of the brain is known as functional integration. Newer research has shown that these different regions of the brain may not be solely responsible for only one sensory modality, but could use multiple inputs to perceive what the body senses about its environment. Multisensory integration is necessary for almost every activity that we perform because the combination of multiple sensory inputs is essential for us to comprehend our surroundings. Examples: One of the earliest sensations is the olfactory sensation. Evolutionary, gustation and olfaction developed together. This multisensory integration was necessary for early humans in order to ensure that they were receiving proper nutrition from their food, and also to make sure that they were not consuming poisonous materials. There are several other sensory integrations that developed early on in the human evolutionary time line. The integration between vision and audition was necessary CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 75 for spatial mapping. Integration between vision and tactile sensations developed along with our finer motor skills including better hand-eye coordination. While humans developed into bipedal organisms, balance became exponentially more essential to survival. The multisensory integration between visual inputs, vestibular (balance) inputs, and proprioception inputs played an important role in our development into upright walkers. 3.3 The Concept of Sensation Sensation is the process that allows our brains to take in information via our five senses, which can then be experienced and interpreted by the brain. Sensation occurs thanks to our five sensory systems: vision, hearing, taste, smell and touch. Each of these systems maintains unique neural pathways with the brain which allows them to transfer information from the environment to the brain very rapidly. Without sensation, we would not be able to enjoy the sunny spring day at the park. Each sensory system contains unique sensory receptors, which are designed to detect specific environmental stimuli. Once detected, sensory receptors convert environmental stimulus energy into electrochemical neural impulses. The brain then interprets those neural messages, which allow the brain to experience and make decisions about the environment. Let’s take a little bit closer look at the process of sensation by examining each of the five sensory systems involved. Definition of Sensation According to Zajonc, “Sensation is the process that allows our brains to take in information via our five senses, which can then be experienced and interpreted by the brain. Sensation occurs thanks to our five sensory systems: vision, hearing, taste, smell and touch”. Differences between Sensation and Perception Sensation occurs when sensory receptors detect sensory stimuli. Perception involves the organization, interpretation, and conscious experience of those sensations. All sensory systems have both absolute and difference thresholds, which refer to the minimum amount of stimulus energy or the minimum amount of difference in stimulus energy required to be detected about 50% of the time, respectively. Sensory adaptation, selective attention, and signal detection theory can help explain what is perceived and what is not. In addition, the perceptions are affected by a number of factors, including beliefs, values, prejudices, culture and life experiences. CU IDOL SELF LEARNING MATERIAL (SLM)

76 Experimental Psychology Sensory receptors are specialized neurons that respond to specific types of stimuli. When sensory information is detected by a sensory receptor, sensation has occurred. For example, light that enters the eye causes chemical changes in cells that line the back of the eye. These cells relay messages, in the form of action potentials (as you learned when studying biopsychology), to the central nervous system. The conversion from sensory stimulus energy to action potential is known as transduction. Perception refers to the way sensory information is organized, interpreted, and consciously experienced. Perception involves both bottom-up and top-down processing. Bottom-up processing refers to the fact that perceptions are built from sensory input. On the other hand, how we interpret those sensations is influenced by our available knowledge, our experiences, and our thoughts. This is called top-down processing. Types of Sensations Various types of sensations are as follows: Visual The wavelength, intensity and complexity of Light are detected by visual receptors in the retina of the eye. There are two types of visual receptors: rods and cones. Rods are sensitive to dim light, which makes them useful for seeing at night. Cones are more sensitive to color and bright light, which makes them more useful in daylight. Signals from rods and cones are transduced into useful neural information via the optic nerve. Blindness is the complete or nearly complete inability to see. Auditory The frequency, intensity, and complexity of sounds waves in the external world are detected by auditory receptors (cilia or hair cell receptors) in the ear. Different patterns of cilia movement lead to different neural codes, which ultimately lead to hearing different loudness, pitch and timbre of sounds. Deafness or hearing loss may occur in one or both ears. Gustatory Taste receptors (i.e., taste buds or papillae) are activated by the presence of food or another object on the tongue. Four basic tastes include sweet, salty, sour and bitter. There is some debate on CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 77 whether umami, or meatiness, is a fifth basic flavor. Aging is associated with loss of intensity in taste. Complete inability to taste is called ageusia. Olfactory Smells in the external world activate hair receptors in nostrils. These receptors then send signals to the olfactory bulb, which is located at the base of the brain. Anosmia is the inability to smell. Somatosensory Somatosensory sensations occur when receptors detect changes on one’s skin or within one’s body. Cutaneous Sensations Sensations on the skin are detected by cutaneous receptors. These receptors may feel sensations such as pain, tickle, cold, hot, soft and rough. Mechanoreceptors detect light pressure (e.g., caress), vibration, and texture, nociceptors detect strong pressure (e.g., pain), and thermoreceptors detect temperature. For example, if your dog lightly presses its nose on your leg, mechanoreceptors in your skin will sense the smooth texture of your dog’s nose whereas thermoreceptors will detect its coldness. When a dog bites someone, nociceptors detect the sharp pressure. Astereognosis is the inability to identify an object by touch. Proprioception Proprioception is the “sense of bodily position.” It includes the vestibular sense (i.e., one’s sense of balance) and kinesthetic sense (i.e., one’s awareness of one’s movements). Osmoreception Osmoreception is the body’s sensation of thirst. When the amount of water in one’s body falls below a certain threshold, the concentration of osmolytes (e.g. salt) increase in one’s blood. Osmoreceptors, or sensory receptors in the hypothalamus, detect these changes in osmotic concentration. These signals are then transferred to neural signals of thirst. CU IDOL SELF LEARNING MATERIAL (SLM)

78 Experimental Psychology 3.4 Structure of Sensory Processes Various elements related to structure of sensory processes are as follows: Step-1: Reception Reception is the first step in the processing of sensation and is dependent on the receptor type, stimulus and receptive field. In more advanced animals, the senses are constantly at work, making the animal aware of stimuli, such as light or sound or the presence of a chemical substance in the external environment, while monitoring information about the organism’s internal environment. All bilaterally symmetric animals have a sensory system. The development of any species’ sensory system has been driven by natural selection; thus, sensory systems differ among species according to the demands of their environments. For example, the shark, unlike most fish predators, is electrosensitive (i.e., sensitive to electrical fields produced by other animals in its environment). While it is helpful to this underwater predator, electrosensitivity is a sense not found in most land animals. Senses provide information about the body and its environment. Humans have five special senses: olfaction (smell), gustation (taste), equilibrium (balance and body position), vision, and hearing. Additionally, we possess general senses, also called somatosensation, which respond to stimuli like temperature, pain, pressure and vibration. Vestibular sensation, which is an organism’s sense of spatial orientation and balance, proprioception (position of bones, joints, and muscles), and the sense of limb position that is used to track kinesthesia (limb movement) are part of somatosensation. Although the sensory systems associated with these senses are very different, all share a common function: to convert a stimulus (light, sound or the position of the body) into an electrical signal in the nervous system. This process is called sensory transduction. There are two broad types of cellular systems that perform sensory transduction. In one, a neuron works with a sensory receptor, a cell, or cell process that is specialized to engage with and detect a specific stimulus. Stimulation of the sensory receptor activates the associated afferent neuron, which carries information about the stimulus to the central nervous system. In the second type of sensory transduction, a sensory nerve ending responds to a stimulus in the internal or external environment; this neuron constitutes the sensory receptor. Free nerve endings can be stimulated by CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 79 several different stimuli, thus showing little receptor specificity. For example, pain receptors in your gums and teeth may be stimulated by temperature changes, chemical stimulation, or pressure. The first step in sensation is reception: the activation of sensory receptors by stimuli such as mechanical stimuli (being bent or squished, for example), chemicals, or temperature. The receptor can then respond to the stimuli. The region in space in which a given sensory receptor can respond to a stimulus, be it far away or in contact with the body, is that receptor’s receptive field. Think for a moment about the differences in receptive fields for the different senses. For the sense of touch, a stimulus must come into contact with body. For the sense of hearing, a stimulus can be a moderate distance away. For vision, a stimulus can be very far away; for example, the visual system perceives light from stars at enormous distances. Step-2: Transduction and Perception Transduction is the process that converts a sensory signal to an electrical signal to be processed in a specialized area in the brain. The most fundamental function of a sensory system is the translation of a sensory signal to an electrical signal in the nervous system. This takes place at the sensory receptor. The change in electrical potential that is produced is called the receptor potential. How is sensory input, such as pressure on the skin, changed to a receptor potential? As an example, a type of receptor called a mechanoreceptor possesses specialized membranes that respond to pressure. Disturbance of these dendrites by compressing them or bending them opens gated ion channels in the plasma membrane of the sensory neuron, changing its electrical potential. In the nervous system, a positive change of a neuron’s electrical potential (also called the membrane potential), depolarizes the neuron. Receptor potentials are graded potentials: the magnitude of these graded (receptor) potentials vary with the strength of the stimulus. If the magnitude of depolarization is sufficient (i.e., if membrane potential reaches a threshold), the neuron will fire an action potential. In most cases, the correct stimulus impinging on a sensory receptor will drive membrane potential in a positive direction, although for some receptors, such as those in the visual system, this is not always the case. Sensory receptors for the various senses work differently from each other. They are specialized according to the type of stimulus they sense; thus, they have receptor specificity. For example, touch receptors, light receptors, and sound receptors are each activated by different stimuli. Touch CU IDOL SELF LEARNING MATERIAL (SLM)

80 Experimental Psychology receptors are not sensitive to light or sound; they are sensitive only to touch or pressure. However, stimuli may be combined at higher levels in the brain, as happens with olfaction, contributing to our sense of taste. Step-3: Encoding and Transmission of Sensory Information Four aspects of sensory information are encoded by sensory systems: the type of stimulus, the location of the stimulus in the receptive field, the duration of the stimulus, and the relative intensity of the stimulus. Thus, action potentials transmitted over a sensory receptor’s afferent axons encode one type of stimulus. This segregation of the senses is preserved in other sensory circuits. For example, auditory receptors transmit signals over their own dedicated system. The electrical activity in the axons of the auditory receptors will be interpreted by the brain as an auditory stimulus: a sound. The intensity of a stimulus is often encoded in the rate of action potentials produced by the sensory receptor. Thus, an intense stimulus will produce a more rapid train of action potentials. Reducing the stimulus will likewise slow the rate of production of action potentials. A second way in which intensity is encoded is by the number of receptors activated. An intense stimulus might initiate action potentials in a large number of adjacent receptors, while a less intense stimulus might stimulate fewer receptors. Integration of sensory information begins as soon as the information is received in the central nervous system. Step-4: Perception Perception is an individual’s interpretation of a sensation. Although perception relies on the activation of sensory receptors, perception happens, not at the level of the sensory receptor, but at the brain level. The brain distinguishes sensory stimuli through a sensory pathway: action potentials from sensory receptors travel along neurons that are dedicated to a particular stimulus. All sensory signals, except those from the olfactory system, are transmitted though the central nervous system: they are routed to the thalamus and to the appropriate region of the cortex. The thalamus is a structure in the forebrain that serves as a clearinghouse and relay station for sensory (as well as motor) signals. When the sensory signal exits the thalamus, it is conducted to the specific area of the cortex dedicated to processing that particular sense. CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 81 Vision: The Visual System, the Eye and Color Vision In the human visual system, the eye receives physical stimuli in the form of light and sends those stimuli as electrical signals to the brain, which interprets the signals as images. The human visual system gives our bodies the ability to see our physical environment. The system requires communication between its major sensory organ (the eye) and the core of the central nervous system (the brain) to interpret external stimuli (light waves) as images. Humans are highly visual creatures compared to many other animals which rely more on smell or hearing, and over our evolutionary history we have developed an incredibly complex sight system. Sensory Organs Vision depends mainly on one sensory organ—the eye. Eye constructions vary in complexity depending on the needs of the organism. The human eye is one of the most complicated structures on earth, and it requires many components to allow our advanced visual capabilities. The eye has three major layers: 1. the sclera, which maintains, protects, and supports the shape of the eye and includes the cornea; 2. the choroid, which provides oxygen and nourishment to the eye and includes the pupil, iris and lens; and 3. the retina, which allows us to piece images together and includes cones and rods. The Process of Sight All vision is based on the perception of electromagnetic rays. These rays pass through the cornea in the form of light; the cornea focuses the rays as they enter the eye through the pupil, the black aperture at the front of the eye. The pupil acts as a gatekeeper, allowing as much or as little light to enter as is necessary to see an image properly. The pigmented area around the pupil is the iris. Along with supplying a person’s eye color, the iris is responsible for acting as the pupil’s stop, or sphincter. Two layers of iris muscles contract or dilate the pupil to change the amount of light that enters the eye. Behind the pupil is the lens, which is similar in shape and function to a camera lens. CU IDOL SELF LEARNING MATERIAL (SLM)

82 Experimental Psychology Together with the cornea, the lens adjusts the focal length of the image being seen onto the back of the eye, the retina. Visual reception occurs at the retina where photoreceptor cells called cones and rods give an image color and shadow. The image is transduced into neural impulses and then transferred through the optic nerve to the rest of the brain for processing. The visual cortex in the brain interprets the image to extract form, meaning, memory and context. Fig. 3.1: Process of Sight Anatomy of the Human Eye A cross-section of the human eye with its component pieces labeled. Clockwise from left: Optic nerve, optic disc, sclera, choroid, retina, zonular fibers, posterior chamber, iris, pupil, cornea, aqueous humor, ciliary muscle, suspensory ligament, fovea and retinal blood vessels. In center: Vitreous humour, hyaloid canal and lens. The left hemisphere of the brain controls the motor functions of the right half of the body, and vice versa; the same is true of vision. The left hemisphere of the brain processes visual images from the right-hand side of space, or the right visual field, and the right hemisphere processes visual images from the left-hand side of space, or the left visual field. The optic chiasm is a complicated crossover of optic nerve fibers behind the eyes at the bottom of the brain, allowing the right eye to CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 83 “wire” to the left neural hemisphere and the left eye to “wire” to the right hemisphere. This allows the visual cortex to receive the same visual field from both eyes. Color Vision Human beings are capable of highly complex vision that allows us to perceive colors and depth in intricate detail. Visual stimulus transduction happens in the retina. Photoreceptor cells found in this region have the specialized capability of phototransduction, or the ability to convert light into electrical signals. There are two types of these photoreceptor cells: rods, which are responsible for scotopic vision (night vision), and cones, which are responsible for photopic vision (daytime vision). Generally speaking, cones are for color vision and rods are for shadows and light differences. The front of your eye has many more cones than rods, while the sides have more rods than cones; for this reason, your peripheral vision is sharper than your direct vision in the darkness, but your peripheral vision is also in black and white. Cones and Rods This density map shows the retina, which is made up of cones and rods. Cones perceive color and rods perceive shadow in images. In the fovea, which is responsible for sharp central vision, there is huge density of cones but no rods. Color vision is a critical component of human vision and plays an important role in both perception and communication. Color sensors are found within cones, which respond to relatively broad color bands in the three basic regions of red, green, and blue (RGB). Any colors in between these three are perceived as different linear combinations of RGB. The eye is much more sensitive to overall light and color intensity than changes in the color itself. Colors have three attributes: brightness, based on luminance and reflectivity; saturation, based on the amount of white present; and hue, based on color combinations. Sophisticated combinations of these receptors signals are transduced into chemical and electrical signals, which are sent to the brain for the dynamic process of color perception. CU IDOL SELF LEARNING MATERIAL (SLM)

84 Experimental Psychology Depth Perception Depth perception refers to our ability to see the world in three dimensions. With this ability, we can interact with the physical world by accurately gauging the distance to a given object. While depth perception is often attributed to binocular vision (vision from two eyes), it also relies heavily on monocular cues (cues from only one eye) to function properly. These cues range from the convergence of our eyes and accommodation of the lens to optical flow and motion. Audition: Hearing, the Ear and Sound Localization The human auditory system allows us to perceive and localize sounds in our physical environment. The human auditory system allows the body to collect and interpret sound waves into meaningful messages. The main sensory organ responsible for the ability to hear is the ear, which can be broken down into the outer ear, middle ear, and inner ear. The inner ear contains the receptor cells necessary for both hearing and equilibrium maintenance. Human beings also have the special ability of being able to estimate where sounds originate from, commonly called sound localization. The Ear The ear is the main sensory organ of the auditory system. It performs the first processing of sound and houses all of the sensory receptors required for hearing. The ear’s three divisions (outer, middle and inner) have specialized functions that combine to allow us to hear. CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 85 Fig. 3.2: The Ear The outer ear is the external portion of the ear, much of which can be seen on the outside of the human head. It includes the pinna, the ear canal, and the most superficial layer of the ear drum, the tympanic membrane. The outer ear’s main task is to gather sound energy and amplify sound pressure. The pinna, the fold of cartilage that surrounds the ear canal, reflects and attenuates sound waves, which helps the brain determine the location of the sound. The sound waves enter the ear canal, which amplifies the sound into the ear drum. Once the wave has vibrated the tympanic membrane, sound enters the middle ear. The middle ear is an air-filled tympanic (drum-like) cavity that transmits acoustic energy from the ear canal to the cochlea in the inner ear. This is accomplished by a series of three bones in the middle ear: the malleus, the incus and the stapes. The malleus (Latin for “hammer”) is connected to the mobile portion of the ear drum. It senses sound vibrations and transfers them onto the incus. The incus (Latin for “anvil”) is the bridge between the malleus and the stapes. The stapes (Latin for “stirrup”) transfers the vibrations from the incus to the oval window, the portion of the inner ear to which it is connected. Through these steps, the middle ear acts as a gatekeeper to the inner ear, protecting it from damage by loud sounds. CU IDOL SELF LEARNING MATERIAL (SLM)

86 Experimental Psychology Unlike the middle ear, the inner ear is filled with fluid. When the stapes footplate pushes down on the oval window in the inner ear, it causes movement in the fluid within the cochlea. The function of the cochlea is to transform mechanical sound waves into electrical or neural signals for use in the brain. Within the cochlea, there are three fluid-filled spaces: the tympanic canal, the vestibular canal, and the middle canal. Fluid movement within these canals stimulates hair cells of the organ of corti, a ribbon of sensory cells along the cochlea. These hair cells transform the fluid waves into electrical impulses using cilia, a specialized type of mechanosensor. The Cochlea A cross-section of the cochlea, the main sensory organ of hearing, located in the inner ear. The Process of Hearing Hearing begins with pressure waves hitting the auditory canal and ends when the brain perceives sounds. Sound reception occurs at the ears, where the pinna collects, reflects, attenuates or amplifies sound waves. These waves travel along the auditory canal until they reach the ear drum, which vibrates in response to the change in pressure caused by the waves. The vibrations of the ear drum cause oscillations in the three bones in the middle ear, the last of which sets the fluid in the cochlea in motion. The cochlea separates sounds according to their place on the frequency spectrum. Hair cells in the cochlea perform the transduction of these sound waves into afferent electrical impulses. Auditory nerve fibers connected to the hair cells form the spiral ganglion, which transmits the electrical signals along the auditory nerve and eventually on to the brain stem. The brain responds to these separate frequencies and composes a complete sound from them. Sound Localization Humans are able to hear a wide variety of sound frequencies, from approximately 20 to 20,000 Hz. Our ability to judge or estimate where a sound originates, called sound localization, is dependent on the hearing ability of each ear and the exact quality of the sound. Since each ear lies on an opposite side of the head, a sound reaches the closest ear first, and the sound’s amplitude will be larger (and therefore louder) in that ear. Much of the brain’s ability to localize sound depends on CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 87 these interaural (between-the-ears) differences in sound intensity and timing. Bushy neurons can resolve time differences as small as ten milliseconds, or approximately the time it takes for sound to pass one ear and reach the other. Gustation: Taste Buds and Taste The gustatory system, including the mouth, tongue, and taste buds, allows us to transduce chemical molecules into specific taste sensations. The gustatory system creates the human sense of taste, allowing us to perceive different flavors from substances that we consume as food and drink. Gustation, along with olfaction (the sense of smell) is classified as chemoreception because it functions by reacting with molecular chemical compounds in a given substance. Specialized cells in the gustatory system that are located on the tongue are called taste buds, and they sense tastants (taste molecules). The taste buds send the information from the tastants to the brain, where a molecule is processed as a certain taste. There are five main tastes: bitter, salty, sweet, sour and umami (savory). All the varieties of flavor we experience are a combination of some or all of these tastes. Fig. 3.3: Taste Buds and Taste CU IDOL SELF LEARNING MATERIAL (SLM)

88 Experimental Psychology The Mouth A cross-section of the human head, which displays the location of the mouth, tongue, pharynx, epiglottis and throat. Tongue and Taste Buds The sense of taste is transduced by taste buds, which are clusters of 50-100 taste receptor cells located in the tongue, soft palate, epiglottis, pharynx and esophagus. The tongue is the main sensory organ of the gustatory system. The tongue contains papillae, or specialized epithelial cells, which have taste buds on their surface. There are three types of papillae with taste buds in the human gustatory system: 1. Fungiform papillae, which are mushroom-shaped and located at the tip of the tongue; 2. Foliate papillae, which are ridges and grooves toward the back of the tongue; 3. Circumvallate papillae, which are circular-shaped and located in a row just in front of the end of the tongue. Each taste bud is flask-like in shape and formed by two types of cells: supporting cells and gustatory cells. Gustatory cells are short-lived and are continuously regenerating. They each contain a taste pore at the surface of the tongue which is the site of sensory transduction. Though there are small differences in sensation, all taste buds, no matter their location, can respond to all types of taste. Tastes Traditionally, humans were thought to have just four main tastes: bitter, salty, sweet and sour. Recently, umami, which is the Japanese word for “savory,” was added to this list of basic tastes. (Spicy is not a basic taste because the sensation of spicy foods does not come from taste buds but rather from heat and pain receptors.) In general, tastes can be appetitive (pleasant) or aversive (unpleasant), depending on the unique makeup of the material being tasted. There is one type of taste receptor for each flavor, and each type of taste stimulus is transduced by a different mechanism. Bitter, sweet, and umami tastes use similar mechanisms based on a G protein-coupled receptor, or GPCR. CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 89 Bitter There are several classes of bitter compounds which vary in chemical makeup. The human body has evolved a particularly sophisticated sense for bitter substances and can distinguish between the many radically different compounds that produce a bitter response. Evolutionary psychologists believe this to be a result of the role of bitterness in human survival: some bitter-tasting compounds can be hazardous to our health, so we learned to recognize and avoid bitter substances in general. Salty The salt receptor, NaCl, is arguable the simplest of all the receptors found in the mouth. An ion channel in the taste cell wall allows Na+ ions to enter the cell. This depolarizes the cell and floods it with ions, leading to a neurotransmitter release. Sweet Like bitter tastes, sweet taste transduction involves GPCRs binding. The specific mechanism depends on the specific molecule flavor. Natural sweeteners such as saccharides activate the GPCRs to release gustducin. Synthetic sweeteners such as saccharin activate a separate set of GPCRs, initiating a similar but different process of protein transitions. Sour Sour tastes signal the presence of acidic compounds in substances. There are three different receptor proteins at work in a sour taste. The first is a simple ion channel which allows hydrogen ions to flow directly into the cell. The second is a K+ channel which has H+ ions in order to block K+ ions from escaping the cell. The third allows sodium ions to flow down the concentration gradient into the cell. This involvement with sodium ions implies a relationship between salty and sour tastes receptors. Umami Umami is the newest receptor to be recognized by western scientists in the family of basic tastes. This Japanese word means “savory” or “meaty.” It is thought that umami receptors act similarly to bitter and sweet receptors (involving GPCRs), but very little is known about their actual function. We do know that umami detects glutamates that are common in meats, cheese, and other protein-heavy foods and reacts specifically to foods treated with MSG. CU IDOL SELF LEARNING MATERIAL (SLM)

90 Experimental Psychology Olfaction: The Nasal Cavity and Smell The olfactory system gives humans their sense of smell by collecting odorants from the environment and transducing them into neural signals. Fig. 3.4: The Nasal Cavity and Smell The olfactory system gives humans their sense of smell by inhaling and detecting odorants in the environment. Olfaction is physiologically related to gustation, the sense of taste, because of its use of chemoreceptors to discern information about substances. Perceiving complex flavors requires recognizing taste and smell sensations at the same time, an interaction known as chemoreceptive sensory interaction. This causes foods to taste different if the olfactory system is compromised. However, olfaction is anatomically different from gustation because it uses the sensory organs of the nose and nasal cavity to capture smells. Humans can identify a large number of odors and use this information to interact successfully with their environment. The Nose and Nasal Cavity Olfactory sensitivity is directly proportional to spatial area in the nose—specifically the olfactory epithelium, which is where odorant reception occurs. The area in the nasal cavity near the septum is CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 91 reserved for the olfactory mucous membrane, where olfactory receptor cells are located. This area is a dime-sized region called the olfactory mucosa. In humans, there are about 10 million olfactory cells, each of which has 350 different receptor types composing the mucous membrane. Each of the 350 receptor types is characteristic of only one odorant type. Each functions using cilia, small hair- like projections that contain olfactory receptor proteins. These proteins carry out the transduction of odorants into electrical signals for neural processing. The Olfactory System A cross-section of the olfactory system that labels all of the structures necessary to process odor information. Olfactory transduction is a series of events in which odor molecules are detected by olfactory receptors. These chemical signals are transformed into electrical signals and sent to the brain, where they are perceived as smells. Once ligands (odorant particles) bind to specific receptors on the external surface of cilia, olfactory transduction is initiated. In mammals, olfactory receptors have been shown to signal via G protein. This is a similar type of signaling of other known G protein-coupled receptors (GPCR). The binding of an odorant particle on an olfactory receptor activates a particular G protein (Gaolf), which then activates adenylate cyclase, leading to cAMP production. cAMP then binds and opens a cyclic nucleotide-gated ion channel. This opening allows for an influx of both Na+ and Ca2+ ions into the cell, thus depolarizing it. The Ca2+ in turn activates chloride channels, causing the departure of Cl–, which results in a further depolarization of the cell. Interpretation of Smells Individual features of odor molecules descend on various parts of the olfactory system in the brain and combine to form a representation of odor. Since most odor molecules have several individual features, the number of possible combinations allows the olfactory system to detect an impressively broad range of smells. A group of odorants that shares some chemical feature and causes similar patterns of neural firing is called an odotope. Humans can differentiate between 10,000 different odors. People (wine or perfume experts, for example) can train their sense of smell to become expert in detecting subtle odors by practicing retrieving smells from memory. CU IDOL SELF LEARNING MATERIAL (SLM)

92 Experimental Psychology Smell and Memory Odor information is easily stored in long-term memory and has strong connections to emotional memory. This is most likely due to the olfactory system’s close anatomical ties to the limbic system and the hippocampus, areas of the brain that have been known to be involved in emotion and place memory. Human and animal brains have this in common: the amygdala, which is involved in the processing of fear, causes olfactory memories of threats to lead animals to avoid dangerous situations. The human sense of smell is not quite as powerful as most other animals’ sense of smell, but smell is still deeply tied to human memory and emotion. Pheromones are airborne, often odorless molecules that are crucial to the behavior of many animals. They are processed by an accessory of the olfactory system. Recent research shows that pheromones play a role in human attraction to potential mates, the synchronization of menstrual cycles among women, and the detection of moods and fear in others. Thanks in large part to the olfactory system, this information can be used to navigate the physical world and collect data about the people around us. Somatosensation: Pressure, Temperature and Pain The somatosensory system allows the human body to perceive the physical sensations of pressure, temperature and pain. Fig. 3.5: Structure of Human Skin CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 93 The human sense of touch is known as the somatic or somatosensory system. Touch is the first sense developed by the body, and the skin is the largest and most complex organ in the somatosensory system. By gathering external stimuli and interpreting them into useful information for the nervous system, skin allows the body to function successfully in the physical world. Touch receptors in the skin have three main subdivisions: mechanoreception (sense of pressure), thermoreception (sense of heat) and nociception (sense of pain). Receptor cells in the muscles and joints called proprioceptors also aid in the somatosensory system, but they are sometimes separated into another sensory category called kinesthesia. Somatosensory Systems The somatosensory system uses specialized receptor cells in the skin and body to detect changes in the environment. The receptors collect and convert physical stimuli into electrical and chemical signals through the transduction process and send these impulses to the nervous system for processing. Sensory cell function in the somatosensory system is determined by location. The receptors in the skin, also called cutaneous receptors, tell the body about the three main subdivisions mentioned above: pressure and surface texture (mechanoreceptors), temperature (thermoreceptors) and pain (nociceptors). The receptors in the muscles and joints provide information about muscle length, muscle tension and joint angles. Mechanoreception Mechanoreceptors in the skin give us a sense of pressure and texture. These receptors differ in their field size (small or large) and their speeds of adaptation (fast or slow). Thus, there are four types of mechanoreceptors based on the four possible combinations of fast vs. slow speed and large vs. small receptive fields. The speed of adaptation refers to how quickly the receptor will react to a stimulus and how long that reaction will be sustained after the stimulus is removed. Rapidly adapting cells allow us to adjust grip and force appropriately. Slowly adapting cells allow us to perceive form and texture. The receptive field size refers to the amount of skin area that responds to the stimulus, with smaller areas specializing in locating stimuli accurately. CU IDOL SELF LEARNING MATERIAL (SLM)

94 Experimental Psychology Thermoreception Thermoreceptors detect changes in temperature through their free nerve endings. There are two types of thermoreceptors that signal temperature changes in our own skin: warm and cold receptors. Our sense of temperature is a result of the comparison of the signals from each of the two types of thermoreceptors. These receptors are not good indicators of absolute temperature, but they are very sensitive to changes in skin temperature. Nociception Nociceptors use free nerve endings to detect pain. Functionally, nociceptors are specialized, high-threshold mechanoceptors or polymodal receptors. They respond not only to intense mechanical stimuli but also to heat and noxious chemicals—anything that may cause the body harm. Their response magnitude, or the amount of pain you feel, is directly related to the degree of tissue damage inflicted. Pain signals can be separated into three types that correspond to the different types of nerve fibers used for transmitting these signals. The first type is a rapidly transmitted signal with a high spatial resolution, called first pain or cutaneous pricking pain. This type of signal is easy to locate and generally easy to tolerate. The second type is much slower and highly affective, called second pain or burning pain. This signal is more difficult to locate and not as easy to tolerate. The third type arises from viscera, musculature, and joints; it is called deep pain. This type of signal is very difficult to locate, and often it is intolerable and chronic. Proprioception Proprioceptors are the receptor cells found in the body’s muscles and joints. They detect joint position and movement, and the direction and velocity of the movement. There are many receptors in the muscles, muscle fascia, joints, and ligaments, all of which are stimulated by stretching in the area in which they lie. Muscle receptors are most active in large joints such as the hip and knee joints, while joint and skin receptors are more meaningful to finger and toe joints. All of these receptors contribute to overall kinesthesia, or the perception of bodily movements. CU IDOL SELF LEARNING MATERIAL (SLM)