MAp 602 7-8

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M.A.(Psy) 2EXPERIMENTAL PSYCHOLOGY All right are reserved with CU-IDOL EXPERIMENTAL PSYCHOLOGY Course Code: MAP 602 Semester: First SLM Unit : 7-8 E-Lesson: 4 www.cuidol.in Unit-7-8 MAP602

EXPERIMENTAL PSYCHOLOGY OBJECTIVES INTRODUCTION 33 After studying this unit, you will be able to: Psychophysics is the scientific study of the Explain the basics of psychophysics relationship between stimuli specified in physical terms and the sensations and Discuss classical psychophysics perceptions evoked by these stimuli. Explain the applicability of signal detection theory Signal Detection Theory is a means to measure the ability to differentiate between Discuss about basic concept of signal detection Information bearing patterns called stimulus theory in living organisms,. www.cuidol.in Unit-7-8 M(AMPA6P02602) INASlTl ITriUgThEt OarFeDrIeSsTeArNvCeEd AwNitDh OCNUL-IIDNOE LLEARNING

> Topics to be covered 4 > > The Concept of Psychophysics EXPERIMENTAL PSYCHOLOGY > Gustav Fechner > Classical Psychophysics > Problem Areas of Interest to Classical Psychophysics > Signal Detection Theory Basic Concept of Signal Detection Theory www.cuidol.in Assumptions of Signal Detection Theory Unit-7-8 MAP602 All right are reserved with CU-IDOL

The Concept of Psychophysics 5 • Psychophysics originated with the research of Gustav Fechner (1801-1887), who first studied the relationship between incoming physical stimuli and the responses to them. • Psychophysicists have generally used two approaches in studying our sensitivity to stimuli around us: measuring the absolute threshold or discovering the difference threshold. In studying the absolute threshold using the method of constant stimuli, an experimenter will, for example, produce an extremely faint tone which the listener cannot hear • The third area of psychophysics involves discrimination of different stimuli, or difference thresholds. No two physical stimuli are absolutely identical, although they may seem to be. www.cuidol.in Unit-7-8 MAP602 All right are reserved with CU-IDOL

The Concept of Psychophysics 6 • The question of interest here is how large must the difference be between two stimuli in order for us to detect it. The amount by which two stimuli must differ in order for us to detect the difference is referred to as the JND, or just noticeable difference. • Research has indicated that for stimuli of low intensity, we can detect a difference that is small, as the intensity increases, www.cuidol.in Unit-7-8 MAP602 All right are reserved with CU-IDOL

Gustav Fechner 7 Gustav Fechner, in full Gustav Theodor Fechner, (born April 19, 1801, Gross Särchen, near Muskau, Lusatia died November 18, 1887, Leipzig, Germany), German physicist and philosopher who was a key figure in the founding of psychophysics, the science concerned with quantitative relations between sensations and the stimuli producing them. • Areas of Investigation by Gustav Fechner The experiments of psychophysicists concentrate on employing physical stimuli and relating them to sensation. These stimuli must be objectively measured; an example of this is the variation of lights in terms of luminance. • Thresholds of Psychophysics Psychophysicists usually employ experimental stimuli that can be objectively measured, such as pure tones varying in intensity, or lights varying in luminance. • Detection An absolute threshold is the level of intensity of a stimulus at which the subject is able to detect the presence of the stimulus some proportion of the time www.cuidol.in Unit-7-8 MAP602 All right are reserved with CU-IDOL

Classical Psychophysics 8 • The classical psychophysics makes reference to a subdivision of the psychological field, in which the central subject is the relationship existing between the sensations experienced by an individual and the environmental stimuli that originate them. • This subfield of study comes to represent a branch of psychology because it intends to explain and represent in a quantitative manner, how the internal process of perception is given. • Sensation instead is considered as a hypothetical construct. We measure stimuli and certain types of behaviors that occur after the stimulus has been presented to the individual. • To explain the consistency of various behaviors scientists have postulated the concept of sensation--an event that happens inside the animal. Sensation is a hypothetical construct, it is not an element of conscious experience which in the past was called sensation. The term \"sensation\" is now a technical term and does not have the meaning given to the word when it is used in everyday, nontechnical conversations www.cuidol.in Unit-7-8 MAP602 All right are reserved with CU-IDOL

Problem Areas of Interest to 9 Classical Psychophysics 1. Threshold determinations--liminal values of stimuli: What amounts of stimuli produce certain types of behavior. 2. Absolute Thresholds (RL). What is the weakest stimulus that will produce a sensation. Defining this stimulus presents several problems because the threshold seemingly varies from moment to moment. 3. In addition we have a conceptual problem. If I flash a weak light one time you either see it or you don't see it. 4. Difference Thresholds (DL). What is the smallest difference between two stimuli which can be sensed. 5. Scaling. These are interested in discovering the way in which sensations (or more operationally defined, the magnitude of our response) increase as the intensity of the stimulus increases. 6. Psychometric Scaling, These are interested in scaling the sensations evoked by stimuli that I cannot measure physically in any meaningful way--meaningful here indicates that whatever mesures www.cuidol.in Unit-7-8 MAP602 All right are reserved with CU-IDOL

Signal Detection Theory Illustration of Signal Detection Theory (SDT) 10 The treat legitimate sites as “non signal,” and phishing sites as “signal.” The sensitivity (d’) measures users’ ability to discern signal from noise. Criterion (C) measures users’ decision tendency. The effects of training could be to a) make the user shift the decision Criterion and thus increasing alertness; b) make users increase sensitivity, separating the two distributions better and thus improving people’s ability to distinguish between phishing and legitimate sites; or c) a combination of both. Internal response probability of occurrence curves for noise-alone and signal-plus-noise trials. Since the curves overlap, the internal response for a noise-alone trial may exceed the internal response for a signal-plus-noise trial. Vertical lines correspond to the criterion response. www.cuidol.in Unit-7-8 MAP602 All right are reserved with CU-IDOL

Basic Concept of Signal 11 Detection Theory • Signal detection theory (SDT) was originally developed to describe the performance of radars, which must detect signals against a background of noise. • As radars become more sensitive (capable of detecting weaker and weaker signals), they are increasingly able to correctly detect when signals are present; these events are called hits, and their probability of occurrence is the hit rate. • However, radars may also mistake noise for signals; these events are false alarms, and the corresponding probability is the false alarm rate. • A challenge similar to the detection of signals by radars arises when humans listen for weak auditory stimuli. A key notion here is that perception involves decision: Was that faint tone simply imagined. www.cuidol.in Unit-7-8 MAP602 All right are reserved with CU-IDOL

Assumptions of Signal Detection Theory 12 1. Sensitivity or discriminability Conceptually, sensitivity refers to how hard or easy it is to detect that a target stimulus is present from background events. For example, in a recognition memory paradigm, having longer to study to-be-remembered words makes it easier to recognize previously seen or heard words 2. Bias Bias is independent of sensitivity. For example, if there is a penalty for either false alarms or misses, this may influence bias. If the stimulus is a bomber, 3. Compressed sensing Another field which is closely related to signal detection theory is called compressed sensing (or compressive sensing). The objective of compressed sensing is to recover high dimensional but with low complexity entities from only a few measurements. 4. Performance decrements in monitoring Performance decrements in monitoring (vigilance) tasks result either from a decrement inobserver sensitivity or from changes in decision criteria www.cuidol.in Unit-7-8 MAP602 All right are reserved with CU-IDOL

Keywords/Abbreviations 13 • Psychophysics - Psychophysics is the scientific study of the relationship between stimuli specified in physical terms. • Gustav Fechner - Psychophysics originated with the research of Gustav Fechner. • Thresholds of Psychophysics - Thresholds can also be ascertained through the methodof constant stimuli. • Signal Detection Theory - Detect a signal • Concept of Signal Detection Theory - Signal detection theory (SDT) is used when psychologists want to measure the way we make decisions under conditions of uncertainty. • Compressed sensing - Another field which is closely related to signal detection theory is called compressed sensing www.cuidol.in Unit-7-8 MAP602 All right are reserved with CU-IDOL

Learning Activity 14 1. You are required to prepare the project report on “Thresholds of Psychophysics”. __________________________________________________________________________________________ __________________________________________________________________________________________ 2. You are suggested to identify the methods of Classical Psychophysics. __________________________________________________________________________________________ __________________________________________________________________________________________ 3. You are required to identify the Basic Concept of Signal Detection Theory. __________________________________________________________________________________________ __________________________________________________________________________________________ 4. You are suggested to prepare the report on “Applications of Signal Detection Theory”. __________________________________________________________________________________________ __________________________________________________________________________________________ www.cuidol.in Unit-7-8 MAP602 All right are reserved with CU-IDOL

Summary 15 • Psychophysics is the scientific study of the relationship between stimuli specified in physical terms and the sensations and perceptions evoked by these stimuli. The term psychophysics is used to denote both the substantive study of stimulus-response relationships and the methodologies used for this study. • Psychophysics deals with the nature of the quantitative relationship between physical and mental qualities. • Psychophysical experiments have traditionally used three methods for testing subjects' perception in stimulus detection and difference detection experiments: the method of limits, the method of constant stimuli and the method of adjustment. • Signal detection theory (SDT) is used when psychologists want to measure the way we make decisions under conditions of uncertainty, such as how we would perceive distances in foggy conditions or during eyewitness identification. • The theory can explain how changing the threshold will affect the ability to discern, often exposing how adapted the system is to the task, purpose or goal at which it is aimed. When the detecting system is a human being, characteristics such as experience, expectations, physiological state (e.g., fatigue) and other factors can affect the threshold applied. www.cuidol.in Unit-7-8 MAP602 All right are reserved with CU-IDOL

Frequently Asked Questions 16 1. Explain the term psychophysics. (For more information see SLM) Ans: The term psychophysics is used to denote both the substantive study of stimulus-response relationships and the methodologies used for this study. Psychophysics deals with the nature of the quantitative relationship between physical and mental qualities. 2. Write the three methods used in psychophysics experiments. (For more information see SLM) Ans: Psychophysical experiments have traditionally used three methods for testing subjects' perception in stimulus detection and difference detection experiments: the method of limits, the method of constant stimuli and the method of adjustment. 3. When is SDT used? (For more information see SLM) Ans: Signal detection theory (SDT) is used when psychologists want to measure the way we make decisions under conditions of uncertainty. 4. While detecting a human being what are the factors effect ? (For more information see SLM) Ans: When the detecting system is a human being, characteristics such as experience, expectations, physiological state (e.g., fatigue) and other factors can affect the threshold applied www.cuidol.in Unit-7-8 MAP602 All right are reserved with CU-IDOL

MULTIPLE CHOICE QUESTIONS 1. Psychologists still use the procedures developed by Fechner and they are still called…………. 17 (a) Complexity methods (b) Psychophysical methods (c) Perception (d) None of the above 2. When the detecting system is a human being, characteristics such as…………. (a) Experience (b) Expectations (c) Physiological state (d) All the above 3. Which of the following is the application of Signal Detection Theory? (a) Sensitivity or discriminability (b) Compressed sensing (c) Performance decrements in monitoring (d) All the above Answers: 1.(b) 2.(b) 3. (c) www.cuidol.in Unit-7-8 MAP602 All right are reserved with CU-IDOL

REFERENCES 18 “References of this unit have been given at the end of the book”. www.cuidol.in Unit-7-8 MAP602 All right are reserved with CU-IDOL

19 THANK YOU www.cuidol.in Unit-7-8 MAP602 All right are reserved with CU-IDOL