MAP602_Experimental Psychology

Sensory Processes: Structure and Function of Eye and Ear 95 Somatic System Disorders A somatic system disorder (formerly called a somatoform disorder) is a type of psychological disorder related to the somatosensory system. Somatic system disorders present symptoms of physical pain or illness that cannot be explained by a medical condition, injury, or substance. The patient must also be excessively worried about his symptoms, and this worry must be judged to be out of proportion to the severity of the physical complaints themselves. 3.5 Structure and Function of Eye The eye receives oxygen through the aqueous. Its function is to nourish the cornea, iris and lens by carrying nutrients; it removes waste products excreted from the lens, and maintains intraocular pressure and thus maintains the shape of the eye. As part of the coursework for becoming certified as a Teacher of Students with Visual Impairments, it is necessary to take a class on the structure and function of the eye. Understanding the significance of each area of the eye can help a TVI understand the possible effects of various visual diagnosis. Fig. 3.6: Function of Eye CU IDOL SELF LEARNING MATERIAL (SLM)

96 Experimental Psychology 1. Tear Layer The Tear Layer (The Lacrimal System) is the first layer of the eye that light strikes. It is clear, moist and salty. Its purpose is to keep the eye smooth and moist. 2. Cornea The Cornea is the second structure that light strikes. It is the clear, transparent front part of the eye that covers the iris, pupil and anterior chamber and provides most of an eye’s optical power (if too flat = hyperopia/farsightedness; if too steep = myopia/nearsightedness). It needs to be smooth, round, clear, and tough. It is like a protective window. The function of the cornea is to let light rays enter the eye and converge the light rays. 3. Anterior Chamber The Anterior Chamber is filled with Aqueous Humor. Aqueous Humour is a clear, watery fluid that fills the space between the back surface of the cornea and the front surface of the vitreous, bathing the lens (The anterior and posterior chambers. Both are located in the front part of the eye, in front of the lens). The eye receives oxygen through the aqueous. Its function is to nourish the cornea, iris, and lens by carrying nutrients, it removes waste products excreted from the lens, and maintain intraocular pressure and thus maintains the shape of the eye. This gives the eye its shape. It must be clear to function properly. 4. Iris The iris is the pigmented tissue lying behind the cornea that gives color to the eye and controls the amount of light entering the eye by varying the size of the papillary opening. It functions like a camera. The color of the iris affects how much light gets in. The iris controls light constantly, adapts to lighting changes, and is responsible for near point reading (to see close, pupils must constrict). Pupil. It is a variable-sized black circular opening in the center of the iris that regulates the amount of light that enters the eye. The pupil needs to be round in order to constrict. CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 97 Constricted. A constricted pupil occurs when the pupil size is reduced to constriction of the iris or relaxation of the iris dilator muscle. The iris constricts with bright illumination, with certain drugs, and can be a consequence of ocular inflammation. Dilated. A dilated pupil is an enlarged pupil, resulting from contraction of the dilator muscle or relaxation of the iris sphincter. It occurs normally in dim illumination, or may be produced by certain drugs (mydriatics) or result from blunt trauma. 5. Lens The lens is the natural lens of the eye (chrystaline lens). Transparent, biconvex intraocular tissue that helps bring rays of light to focus on the retina (It bends light, but not as much as the cornea). Suspended by fine ligaments (zonules) attached between ciliary processes. It has to be clear, has to have a power of about +16, and has to be pliable so it can control refraction (This becomes less pliable as you age leading to presbiopia). Ciliary Body. The circumferential tissue (a ring of tissue between the end of the choroids and the beginning of the iris) inside the eye composed of the ciliary muscle (involved in lens accommodation and control of intraocular pressure and thus the shape of the lens) and 70 ciliary processes that produce aqueous fluid. 6. Vitreous Humor (Chamber) Vitreous Humor (Chamber) is the transparent, colorless gelatinous mass that fills rear two- thirds of the eyeball, between the lens and the retina. It has to be clear so light can pass through it and it has to be there or eye would collapse. 7. Retina The retina is the light sensitive nerve tissue in the eye that converts images from the eye’s optical system into electrical impulses that are sent along the optic nerve to the brain, to interpret as vision. Forms a thin membranous lining of the rear two-thirds of the globe; consists of layers that include two types of cells: rods and cones. There is no retina over the optic nerve which causes a CU IDOL SELF LEARNING MATERIAL (SLM)

98 Experimental Psychology blind spot (This is the sightless area within the visual field of a normal eye. It is caused by absence of light sensitive photoreceptors where the optic nerve enters the eye.) Cones The cones are the light-sensitive retinal receptor cell that provides the sharp visual acuity (detail vision) and color discrimination; most numerous in macular area. Function under bright lighting. Rods The light-sensitive, specialized retinal receptor cell that works at low light levels (night vision). The rods function with movement and provide light/dark contrast. It makes up peripheral vision. Macula It is the “yellow spot” in the small (3°) central area of the retina surrounding the fovea. It is the area of acute central vision (used for reading and discriminating fine detail and color). Within this area is the largest concentration of cones Fovea The fovea is the central pit in the macula that produces the sharpest vision. It contains a high concentration of cones within the macula and no retinal blood vessels. 8. Choroid The vascular (major blood vessel), central layer of the eye lying between the retina and sclera. Its function is to provide nourishment to the outer layers of the retina through blood vessels. It is part of the uveal tract. 9. Sclera The sclera is the opaque, fibrous, tough, protective outer layer of the eye (“white of the eye”) that is directly continuous with the cornea in front and with the sheath covering the optic nerve behind. The sclera provides protection and form. 10. Optic Nerve The Optic Nerve is the largest sensory nerve of the eye. It carries impulses for sight from the retina to the brain. Composed of retinal nerve fibers that exit the eyeball through the optic disc, traverse the orbit, pass through the optic foramen into the cranial cavity, where they meet fibers from the other optic nerve at the optic chiasm. CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 99 Function of Eye Function of eye can be summarized as follows: The structures and functions of the eyes are complex. Each eye constantly adjusts the amount of light it lets in, focuses on objects near and far, and produces continuous images that are instantly transmitted to the brain. The orbit is the bony cavity that contains the eyeball, muscles, nerves, and blood vessels, as well as the structures that produce and drain tears. Each orbit is a pear-shaped structure that is formed by several bones. The outer covering of the eyeball consists of a relatively tough, white layer called the sclera (or white of the eye). Near the front of the eye, in the area protected by the eyelids, the sclera is covered by a thin, transparent membrane (conjunctiva), which runs to the edge of the cornea. The conjunctiva also covers the moist back surface of the eyelids and eyeballs. Light enters the eye through the cornea, the clear, curved layer in front of the iris and pupil. The cornea serves as a protective covering for the front of the eye and also helps focus light on the retina at the back of the eye. After passing through the cornea, light travels through the pupil (the black dot in the middle of the eye). The iris the circular, colored area of the eye that surrounds the pupil controls the amount of light that enters the eye. The iris allows more light into the eye (enlarging or dilating the pupil) when the environment is dark and allows less light into the eye (shrinking or constricting the pupil) when the environment is bright. Thus, the pupil dilates and constricts like the aperture of a camera lens as the amount of light in the immediate surroundings changes. The size of the pupil is controlled by the action of the pupillary sphincter muscle and dilator muscle. CU IDOL SELF LEARNING MATERIAL (SLM)

100 Experimental Psychology Behind the iris sits the lens. By changing its shape, the lens focuses light onto the retina. Through the action of small muscles (called the ciliary muscles), the lens becomes thicker to focus on nearby objects and thinner to focus on distant objects. The retina contains the cells that sense light (photoreceptors) and the blood vessels that nourish them. The most sensitive part of the retina is a small area called the macula, which has millions of tightly packed photoreceptors (the type called cones). The high density of cones in the macula makes the visual image detailed, just as a high-resolution digital camera has more megapixels. Each photoreceptor is linked to a nerve fiber. The nerve fibers from the photoreceptors are bundled together to form the optic nerve. The optic disk, the first part of the optic nerve, is at the back of the eye. The photoreceptors in the retina convert the image into electrical signals, which are carried to the brain by the optic nerve. There are two main types of photoreceptors: cones and rods. Cones are responsible for sharp, detailed central vision and color vision and are clustered mainly in the macula. Rods are responsible for night and peripheral (side) vision. Rods are more numerous than cones and much more sensitive to light, but they do not register color or contribute to detailed central vision as the cones do. Rods are grouped mainly in the peripheral areas of the retina. The eyeball is divided into two sections, each of which is filled with fluid. The pressure generated by these fluids fills out the eyeball and helps maintain its shape. The front section (anterior segment) extends from the inside of the cornea to the front surface of the lens. It is filled with a fluid called the aqueous humor, which nourishes the internal structures. The anterior segment is divided into two chambers. The front (anterior) chamber extends from the cornea to the iris. The back (posterior) chamber extends from the iris to the lens. Normally, the aqueous humor is produced in the posterior chamber, flows slowly through the pupil into the anterior chamber, and then drains out of the eyeball through outflow channels located where the iris meets the cornea. CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 101 The back section (posterior segment) extends from the back surface of the lens to the retina. It contains a jellylike fluid called the vitreous humor. Lens of the Eye: Function The human eye is a very complicated organ, but only a few structures in the eye are important for forming images of the objects that we look at. The cornea is a thin, clear membrane that covers the outer part of the front of the eyeball. It is made primarily of a protein called collagen, which is very tough and strong. As light passes into the eye, it first passes through the cornea. Since the cornea is a curved surface, it acts like a convex lens and begins to focus the light rays. The light then passes through the pupil and hits the lens of the eye. The lens, also convex, further focuses the light so that it will hit the retina at the back of the eyeball. The retina contains specialized cells that are sensitive to light; these are called rods and cones. When the cornea and lens focus light onto the retina, the cells are stimulated and send signals to the brain, allowing you to see. As light rays passes though the cornea and lens, they bend so that they will focus exactly on the retina in the back of the eye. This allows you to form a clear image of the world around you. Lens Retina Cornea Fig. 3.7: Lens of the Eye: Function CU IDOL SELF LEARNING MATERIAL (SLM)

102 Experimental Psychology In the eye, the lens is held in place by tiny ligaments connected to the ciliary muscles. These muscles control the level of tension in the ligaments and therefore control the shape of the lens. When the eye is relaxed, tension in the ligaments causes the lens to be slightly flattened. When the eye focuses on a nearby object nearby object, the ciliary muscles contract, to reduce the tension in the ligaments and cause the lens to become more spherical. As the lens changes shape, it causes the light that passes through it to focus at a different location. This is called accommodation and is what allows your eyes to focus on both near and far objects. By contracting or relaxing the ciliary muscles, you can cause your eyes to focus on an object that is any distance away. 3.6 Structure and Function of Ear The ear has three main parts: external ear, middle ear and inner ear. They all have different, but important, features that facilitate hearing and balance. Hearing The external ear, also called the auricle or pinna, is the loop of cartilage and skin that is attached to outside of the head. It works much like a megaphone. Sound is funneled through the external ear and piped into the external auditory canal, according to Nebraska Medicine. The auditory canal is the part of the ear hole that can easily be seen when looking an ear up close. The sound waves pass through the auditory canal and reach the tympanic membrane, better known as the eardrum. Just like a drum being hit be a drumstick, the thin sheet of connective tissue vibrates when sound waves strike it. The vibrations pass through the tympanic membrane and enter the middle ear, also called the tympanic cavity. The tympanic cavity is lined with mucosa and filled with air and the auditory ossicles, which are three tiny bones called the malleus (hammer), incus (anvil), and stapes (stirrup), according to Encyclopedia Britannica. As the bones vibrate, the stapes pushes a structure called the oval window in and out, according to the National Library of Medicine (NLM). This action is passed on to the inner ear and the CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 103 cochlea, a fluid-filled, spiral-shaped structure that contains the spiral organ of Corti, which is the receptor organ for hearing. Tiny hair cells in this organ translate the vibrations into electrical impulses that are carried to the brain by sensory nerves. Anatomy of the Ear Osalcles: Temporal bone Semicircular ducts steps Vestibular nerve Incus Malleus Cochlear nerve Cochlea Aurlcle Earlobe Fig. 3.8: Hearing Balance The Eustachian tube, or pharyngotympanic tube, in the middle ear equalizes air pressure in the middle ear with the air pressure in the atmosphere. This process helps humans retain their balance. The vestibular complex, in the inner ear, is also important to balance because it contains receptors that regulate a sense of equilibrium. The inner ear is connected to the vestibulocochlear nerve, which carries sound and equilibrium information to the brain. Diseases and Conditions Ears are delicate organs that can often have problems due to damage, bacteria or even changes in the environment. Ear infections are the most common illness in babies and younger children, according to the NLM. Common symptoms of ear infections are drainage from the ear, hearing loss, earache, fever, CU IDOL SELF LEARNING MATERIAL (SLM)

104 Experimental Psychology headaches, pain in the ear and a feeling of fullness in the ear, according to the American Academy of Family Physicians. Meniere’s disease a disease of the inner ear that may be the result of fluid problems inside the ear. Symptoms include hearing loss, pressure or pain, dizziness and tinnitus. Tinnitus is a roaring in the ears. It can also be caused by loud noises, medicines or a variety of other causes. Ear barotrauma is an injury to the ear due to changes in barometric or water pressure, according to the NLM. It typically occurs during flights in an airplane, traveling to places at high altitudes or diving into deep waters. Symptoms include pain, stuffy ears, hearing loss and dizziness. Barotrauma can usually be fixed by “popping” the ears by yawning, chewing gum or trying to blow outward while keeping the nose pinched and mouth closed. Ear wax, also called cerumen, has antibacterial properties and also lubricates and protects the ear. Normal amounts shouldn’t bother most people, though sometimes, wax can build up and should be removed, according to The American Academy of Otolaryngology. Symptoms of wax build-up is a feeling of blockage in the ears, coughing, odor, discharge, itching and hearing loss. Hearing typically declines with age naturally, though damage to the ear can cause hearing loss at a very young age. “We are seeing more and more patients with significant hearing loss as early as the late teenaged years,” Dr. Sreekant Cherukuri, a board-certified otolaryngologist based in Chicago and the founder of MDHearingAid, told Live Science. “Noise-induced hearing loss is a growing problem in this country. We are connected to phones and music players, often for hours each day. When our ears are exposed to harmful noise, delicate cells in the inner ear become damaged. Unfortunately, the damage is cumulative over time.” Promoting Good Ear Health Once hearing is gone, it is impossible to repair it naturally. Most patients with hearing loss need surgery or hearing aids. “The good news is that this is 100% preventable,” said Cherukuri. “I tell my patients to follow the 60-60 rule when they use earbuds or headphones: no more than 60 percent of full volume for no longer than 60 minutes at a time.” CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 105 People who participate in noisy activities or hobbies, such as sporting events, music concerts, shooting sports, motorcycle riding or mowing the lawn, should also wear earplugs or noise-canceling or noise-blocking headphones to help protect the ears. Careful cleaning is another way to prevent hearing loss and damage. The American Academy of Otolaryngology suggests cleaning the external ear with a cloth. Then, put a few drops of mineral oil, baby oil, glycerin, or commercial drops in the ear to soften the wax and help it drain out of the ear. A few drops of hydrogen peroxide or carbamide peroxide may also help. Never insert anything into the ear. How the Eustachian Tube Functions? The inner ear is sensitive to pressure changes and requires a valve that can open and close to equalize air and fluid imbalances. This valve is called the Eustachian tube. There is one Eustachian tube in each ear, connecting the middle ear to the back of the throat. The tubes are about an inch long, and the narrowest part is the end that connects to the middle ear. Outer Middle Inner ear ear ear Semicircular canals Pinna (auricle) External ear Cochlea (auditory) canal Eustachian tube Tympanic membran Ossicles (ear drum) Fig. 3.9: Eustachian Tube Functions CU IDOL SELF LEARNING MATERIAL (SLM)

106 Experimental Psychology The middle ear is normally filled with air, allowing sound to flow through to the brain. When a person swallows or yawns, the Eustachian tube opens briefly, restoring air that has been absorbed by the middle ear lining and equalizing pressure in the ear. If the Eustachian tube cannot open, a person may suffer hearing impairment, ear pain, a sensation of fullness in one or both ears, tinnitus, and other symptoms. Eustachian Tube Problems Related to Changes in Altitude It is common for people who have Eustachian tube problems to have difficulty equalizing middle ear pressure when flying. Pressure changes occur rapidly during an airplane’s takeoff and landing procedures: when an aircraft takes off, the atmospheric pressure decreases, increasing middle ear air pressure. When it descends, atmospheric pressure increases, decreasing middle ear pressure. Discomfort is more commonly felt as a plane lands, but can be uncomfortable at any point in a flight if the cabin pressure changes. There are many ways people can prevent Eustachian tube problems associated with flying, including: 1. Avoiding high-risk situations. People who are suffering from acute upper respiratory ailments, such as a common cold, severe allergies, or sinus infections, should avoid flying. 2. Taking a decongestant. People who have chronic Eustachian tube problems can prepare for air travel ahead of time by taking Sudafed tablets according to package directions the day before the flight. 3. Using nasal spray. Travelers should pack a plastic squeeze bottle of 1/4 percent Neo Synephrine or Afrin nasal spray in their carry-on luggage. Travelers should use the nasal spray once according to package directions shortly before boarding, and again forty-five minutes before the plane is due to land. 4. Swallowing and yawning. If your ears “plug up” as the plane takes off, hold your nose and swallow while attempting to force air up to the back of the throat. This will suck CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 107 excess air pressure out of the middle ear. Yawning can also stimulate the Eustachian tubes to open, and can be done continually while landing. 5. Chewing gum. Chewing gum stimulates swallowing and encourages the Eustachian tubes to open. While chewing, you can hold your nose and blow gently toward the back of the throat while swallowing (known as the Valsalva Maneuver) if you feel pressure building behind your ears. 3.7 Summary 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. 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. 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. CU IDOL SELF LEARNING MATERIAL (SLM)

108 Experimental Psychology 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. 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. The eye receives oxygen through the aqueous. Its function is to nourish the cornea, iris, and lens by carrying nutrients; it removes waste products excreted from the lens, and maintains intraocular pressure and thus maintains the shape of the eye. The external ear, also called the auricle or pinna, is the loop of cartilage and skin that is attached to outside of the head. It works much like a megaphone. Sound is funneled through the external ear and piped into the external auditory canal, according to Nebraska Medicine. The auditory canal is the part of the ear hole that can easily be seen when looking an ear up close. 3.8 Key Words/Abbreviations  Sensory Process: Sensory processing is the process that organizes sensation from one’s own body and the environment. CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 109  Sensation: Sensation is the process that allows our brains to take in information via our five senses.  Visual: The wavelength, intensity and complexity of Light are detected by visual receptors in the retina of the eye.  Auditory: The frequency, intensity, and complexity of sounds waves in the external world are detected by auditory receptors in the ear.  Gustatory: Taste receptors are activated by the presence of food or another object on the tongue  Olfactory: Smells in the external world activate hair receptors in nostrils.  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.  Proprioception: Proprioception is the “sense of bodily position.”  Osmoreception: Osmoreception is the body’s sensation of thirst.  Perception: Perception is an individual’s interpretation of a sensation. 3.9 Learning Activity 1. You are required to identify about Sensory Process. _________________________________________________________________ _________________________________________________________________ 2. You are suggested to prepare a team of 10 members and work on structure of Sensory Processes. _________________________________________________________________ _________________________________________________________________ CU IDOL SELF LEARNING MATERIAL (SLM)

110 Experimental Psychology 3. You are required to prepare a report on “structure and Function of Ear and Eye”. _________________________________________________________________ _________________________________________________________________ 3.10 Unit End Exercises (MCQs and Descriptive) A. Descriptive Type Questions 1. Give the meaning of Sensory Process. 2. Discuss the concept of Sensation. 3. Explain various types of Sensations. 4. Discuss the structure of Sensory Processes. 5. Explain the process of Hearing. 6. Explain the structure and function of Eye. 7. Discuss the structure and function of Ear. 8. Explain the promoting good ear health. B. Multiple Choice Questions 1. Which of the following 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? (a) Sensory processing (b) Multisensory integration (c) Sensory modality (d) All the above CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Eye and Ear 111 2. Sensory processing deals with how the brain processes multiple sensory modality inputs, such as __________. (a) Proprioception (b) Vision (c) Auditory system (d) All the above 3. Which of the following is the element related to Structure of Sensory Processes? (a) Reception (b) Transduction (c) Encoding and Transmission (d) All the above 4. Which of the following is the part of ear? (a) External ear (b) Middle ear (c) Inner ear (d) All the above 5. Which of the following begins with pressure waves hitting the auditory canal and ends when the brain perceives sounds? (a) Hearing (b) Talking (c) Discussion (d) Conference Answers: 1. (a), 2. (d), 3. (d), 4. (d), 5. (a) 3.11 References References of this unit have been given at the end of the book.  CU IDOL SELF LEARNING MATERIAL (SLM)

112 Experimental Psychology UNIT 4 SENSORY PROCESSES: STRUCTURE AND FUNCTION OF OLFACTORY Structure: 4.0 Learning Objectives 4.1 Introduction 4.2 The Olfactory System 4.3 Sense of Smell 4.4 Structure and Function of Olfactory 4.5 Causes of Olfactory Dysfunction 4.6 Summary 4.7 Key Words/Abbreviations 4.8 LearningActivity 4.9 Unit End Exercises (MCQs and Descriptive) 4.10 References 4.0 Learning Objectives After studying this unit, you will be able to:  Explain the sensory processes of Olfactory  Discuss the causes of olfactory dysfunction CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Olfactory 113 4.1 Introduction Olfaction is a chemoreception that forms the sense of smell. Olfaction has many purposes, such as the detection of hazards, pheromones and food. It integrates with other senses to form the sense of flavor. Olfaction occurs when odorants bind to specific sites on olfactory receptors located in the nasal cavity. Glomeruli aggregate signals from these receptors and transmit them to the olfactory bulb, where the sensory input will start to interact with parts of the brain responsible for smell identification, memory and emotion. Often, land organisms will have separate olfaction systems for smell and taste (orthonasal smell and retronasal smell), but water-dwelling organisms usually have only one system. Olfactory dysfunction arises as the result of many different peripheral and central disturbances, including upper respiratory infections, traumatic brain injury and neurodegenerative disease. 4.2 The Olfactory System The olfactory system, or sense of smell, is the sensory system used for smelling (olfaction). Olfaction is one of the special senses that have directly associated specific organs. Most mammals and reptiles have a main olfactory system and an accessory olfactory system. The main olfactory system detects airborne substances, while the accessory system senses fluid-phase stimuli. The senses of smell and taste (gustatory system) are often referred to together as the chemosensory system, because they both give the brain information about the chemical composition of objects through a process called transduction. Fig. 4.1: The Olfactory System CU IDOL SELF LEARNING MATERIAL (SLM)

114 Experimental Psychology Clinical Significance Olfactory problems can be divided into different types based on their malfunction. The olfactory dysfunction can be total (anosmia), incomplete (partial anosmia, hyposmia, or microsmia), distorted (dysosmia), or can be characterized by spontaneous sensations like phantosmia. An inability to recognize odors despite a normally functioning olfactory system is termed olfactory agnosia. Hyperosmia is a rare condition typified by an abnormally heightened sense of smell. Like vision and hearing, the olfactory problems can be bilateral or unilateral meaning if a person has anosmia on the right side of the nose but not the left, it is a unilateral right anosmia. On the other hand, if it is on both sides of the nose, it is called bilateral anosmia or total anosmia. Destruction to olfactory bulb, tract and primary cortex (brodmann area 34) results in anosmia on the same side as the destruction. Also, irritative lesion of the uncus results in olfactory hallucinations. Olfactory System Thalamus (medical Orbitorontal cortex dorsal nucleus) Olfactory bulb Olfactory Diffuse bulb projections Cribriform tothe plate limbic system Olfactory receptor cells Nasal passage Fig. 4.2: Clinical Significance Damage to the olfactory system can occur by traumatic brain injury, cancer, infection, inhalation of toxic fumes or neurodegenerative diseases such as Parkinson’s disease and Alzheimer’s disease. These conditions can cause anosmia. In contrast, recent finding suggested the molecular aspects of CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Olfactory 115 olfactory dysfunction can be recognized as a hallmark of amyloidogenesis-related diseases and there may even be a causal link through the disruption of multivalent metal ion transport and storage. Doctors can detect damage to the olfactory system by presenting the patient with odors via a scratch and sniff card or by having the patient close their eyes and try to identify commonly available odors like coffee or peppermint candy. Doctors must exclude other diseases that inhibit or eliminate ‘the sense of smell’ such as chronic colds or sinusitis before making the diagnosis that there is permanent damage to the olfactory system. 4.3 Sense of Smell The sense of smell works by the detection of odors. Olfactory epithelium located in the nose contains millions of chemical receptors that detect odors. When we sniff, chemicals in the air are dissolved in mucus. Odor receptor neurons in olfactory epithelium detect these odors and send the signals on to the olfactory bulbs. These signals are then sent along olfactory tracts to the olfactory cortex of the brain through sensory transduction. Olfacotory bulb 4. The signals are transmitted to higher regions of the brain. 3. The signals are relayed via converged axons. Olfacotory nerve Olfactory 2. Olfactory receptor Olfacotory bulb receptor cells cells are activated Receptor cells and send electrical in olfactory signals. membrane 1. Odorants bind to Odor molecules receptors. Odorant receptors Air with odorant molecules Fig. 4.3: Sense of Smell The olfactory cortex is vital for the processing and perception of odor. It is located in the temporal lobe of the brain, which is involved in organizing sensory input. The olfactory cortex is also CU IDOL SELF LEARNING MATERIAL (SLM)

116 Experimental Psychology a component of the limbic system. This system is involved in the processing of our emotions, survival instincts and memory formation. The olfactory cortex has connections with other limbic system structures such as the amygdala, hippocampus and hypothalamus. The amygdala is involved in forming emotional responses (particularly fear responses) and memories, the hippocampus indexes and stores memories, and the hypothalamus regulates emotional responses. It is the limbic system that connects senses, such as odors, to our memories and emotions. Sense of Smell and Emotions The connection between our sense of smell and emotions is unlike that of the other senses because olfactory system nerves connect directly to brain structures of the limbic system. Odors can trigger both positive and negative emotions as aromas are associated with specific memories. Nerve fibers to brain Receptor cells Olfactory tract Olfactory bulb Gilia Airborne odors Food chemicals Taste (gustatory) nerve to brain Fig. 4.4: Sense of Smell and Emotions Additionally, studies have demonstrated that the emotional expressions of others can influence our olfactory sense. This is due to activity of an area of the brain known as the piriform cortex which is activated prior to odor sensation. CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Olfactory 117 The piriform cortex processes visual information and creates an expectation that a particular fragrance will smell pleasant or unpleasant. Therefore, when we see a person with a disgusted facial expression before sensing an odor, there is an expectation that the odor is unpleasant. This expectation influences how we perceive the odor. Odor Pathways Odors are detected through two pathways. The first is the orthonasal pathway which involves odors that are sniffed in through the nose. The second is the retronasal pathway which is a pathway that connects the top of the throat to the nasal cavity. In the orthonasal pathway, odors that enter the nasal passages are detected by chemical receptors in the nose. The retronasal pathway involves aromas that are contained within the foods we eat. As we chew food, odors are released that travel through the retronasal pathway connecting the throat to the nasal cavity. Once in the nasal cavity, these chemicals are detected by olfactory receptor cells in the nose. Should the retronasal pathway become blocked, the aromas in foods we eat cannot reach odor detecting cells in the nose. As such, the flavors in the food cannot be detected. This often happens when a person has a cold or sinus infection. Smell Disorders Individuals with smell disorders have difficulty detecting or perceiving odors. These difficulties may result from factors such as smoking, aging, upper respiratory infection, head injury and exposure to chemicals or radiation. Anosmia is a condition defined by the inability to detect odors. Other types of smell defects include parosmia (a distorted perception of odors) and phantosmia (odors are hallucinated.) Hyposmia, the diminished sense of smell, is also linked to the development of neurodegenerative diseases such as Parkinson’s and Alzheimer’s disease. CU IDOL SELF LEARNING MATERIAL (SLM)

118 Experimental Psychology 4.4 Structure and Function of Olfactory The olfactory system is responsible for our sense of smell. This sense, also known as olfaction, is one of our five main senses and involves the detection and identification of molecules in the air. Once detected by sensory organs, nerve signals are sent to the brain where the signals are processed. Our sense of smell is closely linked our sense of taste as both rely on the perception of molecules. It is our sense of smell that allows us to detect the flavors in the foods we eat. Olfaction is one of our most powerful senses. Our sense of smell can ignite memories as well as influence our mood and behavior. Limbic system of the brain Olfactory bulb Nasal cavity Aromatic substances Olfactory neurons Fig. 4.5: Function of Olfactory The sense of smell is a complex process that depends on sensory organs, nerves and the brain. Structures of the olfactory system include: 1. Nose: Opening containing nasal passages that allows outside air to flow into the nasal cavity. Also a component of the respiratory system, it humidifies, filters, and warms the air inside the nose. 2. Nasal Cavity: Cavity divided by the nasal septum into left and right passages. It is lined with mucosa. CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Olfactory 119 3. Olfactory Epithelium: Specialized type of epithelial tissue in nasal cavities that contains olfactory nerve cells and receptor nerve cells. These cells send impulses to the olfactory bulb. 4. Cribriform Plate: A porous extension of the ethmoid bone, which separates the nasal cavity from the brain. Olfactory nerve fibers extend through the holes in the cribriform to reach the olfactory bulbs. 5. Olfactory Nerve: Nerve (first cranial nerve) involved in olfaction. Olfactory nerve fibers extend from the mucous membrane, through the cribriform plate, to the olfactory bulbs. 6. Olfactory Bulbs: Bulb-shaped structures in the forebrain where olfactory nerves end and the olfactory tract begins. 7. Olfactory Tract: Band of nerve fibers that extend from each olfactory bulb to the olfactory cortex of the brain. 8. Olfactory Cortex: Area of the cerebral cortex that processes information about odors and receives nerve signals from the olfactory bulbs. 4.5 Causes of Olfactory Dysfunction The common causes of olfactory dysfunction: advanced age, viral infections, exposure to toxic chemicals, head trauma and neurodegenerative diseases. Age Age is the strongest reason for olfactory decline in healthy adults, having even greater impact than does cigarette smoking. Age-related changes in smell function often go unnoticed and smell ability is rarely tested clinically unlike hearing and vision. 2% of people under 65 years of age have chronic smelling problems. This increases greatly between people of ages 65 and 80 with about half experiencing significant problems smelling. Then for adults over 80, the numbers rise to almost 75%. The basis for age-related changes in smell function include closure of the cribriform plate, and cumulative damage to the olfactory receptors from repeated viral and other insults throughout life. CU IDOL SELF LEARNING MATERIAL (SLM)

120 Experimental Psychology Viral Infections The most common cause of permanent hyposmia and anosmia are upper respiratory infections. Such dysfunctions show no change over time and can sometimes reflect damage not only to the olfactory epithelium, but also to the central olfactory structures as a result of viral invasions into the brain. Among these virus-related disorders are the common cold, hepatitis, influenza and influenza- like illness, as well as herpes. Most viral infections are unrecognizable because they are so mild or entirely asymptomatic. Exposure to Toxic Chemicals Chronic exposure to some airborne toxins such as herbicides, pesticides, solvents and heavy metals (cadmium, chromium, nickel and manganese), can alter the ability to smell. These agents not only damage the olfactory epithelium, but they are likely to enter the brain via the olfactory mucosa. Head Trauma Trauma-related olfactory dysfunction depends on the severity of the trauma and whether strong acceleration/deceleration of the head occurred. Occipital and side impact causes more damage to the olfactory system than frontal impact. Neurodegenerative Diseases Neurologists have observed that olfactory dysfunction is a cardinal feature of several neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease. Most of these patients are unaware of an olfactory deficit until after testing where 85% to 90% of early-stage patients showed decrease activity in central odor processing structures. Other neurodegenerative diseases that affect olfactory dysfunction include Huntington’s disease, multi-infarct dementia, amyotrophic lateral sclerosis and schizophrenia. These diseases have more moderate effects on the olfactory system than Alzheimer’s or Parkinson’s diseases. Furthermore, progressive supranuclear palsy and parkinsonism are associated with only minor olfactory problems. These findings have led to the suggestion that olfactory testing may help in the diagnosis of several different neurodegenerative diseases. Neurodegenerative diseases with well-established genetic determinants are also associated with olfactory dysfunction. Such dysfunction, for example, is found in patients with familial Parkinson’s CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Olfactory 121 disease and those with Down syndrome. Further studies have concluded that the olfactory loss may be associated with intellectual disability, rather than any Alzheimer’s disease-like pathology. Huntington’s disease is also associated with problems in odor identification, detection, discrimination and memory. The problem is prevalent once the phenotypic elements of the disorder appear, although it is unknown how far in advance the olfactory loss precedes the phenotypic expression. 4.6 Summary Olfaction is a chemoreception that forms the sense of smell. Olfaction has many purposes, such as the detection of hazards, pheromones and food. It integrates with other senses to form the sense of flavor. Olfaction occurs when odorants bind to specific sites on olfactory receptors located in the nasal cavity. Glomeruli aggregate signals from these receptors and transmit them to the olfactory bulb, where the sensory input will start to interact with parts of the brain responsible for smell identification, memory and emotion. Often, land organisms will have separate olfaction systems for smell and taste (orthonasal smell and retronasal smell), but water-dwelling organisms usually have only one system. Olfactory dysfunction arises as the result of many different peripheral and central disturbances, including upper respiratory infections, traumatic brain injury and neurodegenerative disease. The olfactory system, or sense of smell, is the sensory system used for smelling (olfaction). Olfaction is one of the special senses that have directly associated specific organs. Most mammals and reptiles have a main olfactory system and an accessory olfactory system. The main olfactory system detects airborne substances, while the accessory system senses fluid-phase stimuli. The senses of smell and taste (gustatory system) are often referred to together as the chemosensory system, because they both give the brain information about the chemical composition of objects through a process called transduction. Olfactory problems can be divided into different types based on their malfunction. The olfactory dysfunction can be total (anosmia), incomplete (partial anosmia, hyposmia or microsmia), distorted (dysosmia), or can be characterized by spontaneous sensations like phantosmia. An inability to recognize odors despite a normally functioning olfactory system is termed olfactory agnosia. CU IDOL SELF LEARNING MATERIAL (SLM)

122 Experimental Psychology Hyperosmia is a rare condition typified by an abnormally heightened sense of smell. Like vision and hearing, the olfactory problems can be bilateral or unilateral meaning if a person has anosmia on the right side of the nose but not the left, it is a unilateral right anosmia. On the other hand, if it is on both sides of the nose, it is called bilateral anosmia or total anosmia. Age is the strongest reason for olfactory decline in healthy adults, having even greater impact than does cigarette smoking. Age-related changes in smell function often go unnoticed and smell ability is rarely tested clinically unlike hearing and vision. 2% of people under 65 years of age have chronic smelling problems. This increases greatly between people of ages 65 and 80 with about half experiencing significant problems smelling. Then for adults over 80, the numbers rise to almost 75%. The basis for age-related changes in smell function include closure of the cribriform plate, and cumulative damage to the olfactory receptors from repeated viral and other insults throughout life. The most common cause of permanent hyposmia and anosmia are upper respiratory infections. Such dysfunctions show no change over time and can sometimes reflect damage not only to the olfactory epithelium, but also to the central olfactory structures as a result of viral invasions into the brain. Among these virus-related disorders are the common cold, hepatitis, influenza and influenza- like illness, as well as herpes. Most viral infections are unrecognizable because they are so mild or entirely asymptomatic. Chronic exposure to some airborne toxins such as herbicides, pesticides, solvents, and heavy metals (cadmium, chromium, nickel and manganese), can alter the ability to smell. These agents not only damage the olfactory epithelium, but they are likely to enter the brain via the olfactory mucosa. Trauma-related olfactory dysfunction depends on the severity of the trauma and whether strong acceleration/deceleration of the head occurred. Occipital and side impact causes more damage to the olfactory system than frontal impact. Neurologists have observed that olfactory dysfunction is a cardinal feature of several neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease. Most of these patients are unaware of an olfactory deficit until after testing where 85% to 90% of early-stage patients showed decrease activity in central odor processing structures. Other neurodegenerative diseases that affect olfactory dysfunction include Huntington’s disease, multi-infarct dementia, amyotrophic lateral sclerosis and schizophrenia. These diseases have more CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Olfactory 123 moderate effects on the olfactory system than Alzheimer’s or Parkinson’s diseases. Furthermore, progressive supranuclear palsy and Parkinsonism are associated with only minor olfactory problems. These findings have led to the suggestion that olfactory testing may help in the diagnosis of several different neurodegenerative diseases. Neurodegenerative diseases with well-established genetic determinants are also associated with olfactory dysfunction. Such dysfunction, for example, is found in patients with familial Parkinson’s disease and those with Down syndrome. Further studies have concluded that the olfactory loss may be associated with intellectual disability, rather than any Alzheimer’s disease-like pathology. Huntington’s disease is also associated with problems in odor identification, detection, discrimination and memory. The problem is prevalent once the phenotypic elements of the disorder appear, although it is unknown how far in advance the olfactory loss precedes the phenotypic expression. The olfactory system is responsible for our sense of smell. This sense, also known as olfaction, is one of our five main senses and involves the detection and identification of molecules in the air. Once detected by sensory organs, nerve signals are sent to the brain where the signals are processed. Our sense of smell is closely linked our sense of taste as both rely on the perception of molecules. It is our sense of smell that allows us to detect the flavors in the foods we eat. Olfaction is one of our most powerful senses. Our sense of smell can ignite memories as well as influence our mood and behavior. The sense of smell works by the detection of odors. Olfactory epithelium located in the nose contains millions of chemical receptors that detect odors. When we sniff, chemicals in the air are dissolved in mucus. Odor receptor neurons in olfactory epithelium detect these odors and send the signals on to the olfactory bulbs. These signals are then sent along olfactory tracts to the olfactory cortex of the brain through sensory transduction. The olfactory cortex is vital for the processing and perception of odor. It is located in the CU IDOL SELF LEARNING MATERIAL (SLM)

124 Experimental Psychology temporal lobe of the brain, which is involved in organizing sensory input. The olfactory cortex is also a component of the limbic system. This system is involved in the processing of our emotions, survival instincts, and memory formation. The olfactory cortex has connections with other limbic system structures such as the amygdala, hippocampus, and hypothalamus. The amygdala is involved in forming emotional responses (particularly fear responses) and memories, the hippocampus indexes and stores memories, and the hypothalamus regulates emotional responses. It is the limbic system that connects senses, such as odors, to our memories and emotions. The connection between our sense of smell and emotions is unlike that of the other senses because olfactory system nerves connect directly to brain structures of the limbic system. Odors can trigger both positive and negative emotions as aromas are associated with specific memories. Odors are detected through two pathways. The first is the orthonasal pathway which involves odors that are sniffed in through the nose. The second is the retronasal pathway which is a pathway that connects the top of the throat to the nasal cavity. Individuals with smell disorders have difficulty detecting or perceiving odors. These difficulties may result from factors such as smoking, aging, upper respiratory infection, head injury, and exposure to chemicals or radiation. Anosmia is a condition defined by the inability to detect odors. Other types of smell defects include parosmia (a distorted perception of odors) and phantosmia (odors are hallucinated.) Hyposmia, the diminished sense of smell, is also linked to the development of neurodegenerative diseases such as Parkinson’s and Alzheimer’s disease. CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Olfactory 125 4.7 Key Words/Abbreviations  Olfactory System: The olfactory system, or sense of smell, is the sensory system used for smelling (olfaction).  Advanced Age: Age is the strongest reason for olfactory decline in healthy adults.  Viral Infections: The most common cause of permanent hyposmia and anosmia are upper respiratory infections.  Head Trauma: Trauma-related olfactory dysfunction depends on the severity of the trauma and whether strong acceleration/deceleration of the head occurred.  Neurodegenerative Diseases: Neurologists have observed that olfactory dysfunction is a cardinal feature of several neurodegenerative diseases.  Nasal Cavity: Cavity divided by the nasal septum into left and right passages. It is lined with mucosa.  Olfactory Epithelium: Specialized type of epithelial tissue in nasal cavities that contains olfactory nerve cells and receptor nerve cells.  Olfactory Nerve: Nerve (first cranial nerve) involved in olfaction.  Olfactory Tract: Band of nerve fibers that extend from each olfactory bulb to the olfactory cortex of the brain.  Olfactory Cortex: Area of the cerebral cortex that processes information about odors and receives nerve signals from the olfactory bulbs.  Sense of Smell - The connection between our sense of smell and emotions.  Odor Pathway - Odors are detected through two pathways. CU IDOL SELF LEARNING MATERIAL (SLM)

126 Experimental Psychology 4.8 Learning Activity 1. You are suggested to prepare a report on “the Olfactory System”. _________________________________________________________________ _________________________________________________________________ 2. You are required to identify the causes of Olfactory Dysfunction and structure and function of olfactory. _________________________________________________________________ _________________________________________________________________ 4.9 Unit End Exercises (MCQs and Descriptive) A. Descriptive Type Questions 1. Explain in details about the Olfactory System. 2. Discuss in brief about Clinical significance. 3. Explain various causes of Olfactory Dysfunction. 4. Discuss about structure and function of olfactory. 5. Explain in details about Sense of Smell. 6. Write note on: Odor Pathways and Smell Disorders. B. Multiple Choice Questions 1. Which of the following is a chemoreception that forms the sense of smell? (a) Olfaction (b) Emotion (c) Brain responsible (d) All the above CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Olfactory 127 2. Hyperosmia is a rare condition typified by an abnormally heightened __________. (a) Sense of smell (b) Destruction (c) Olfactory bulb (d) None of the above 3. The common causes of olfactory dysfunction __________. (a) Advanced age (b) Viral infections (c) Exposure to toxic chemicals (d) All the above 4. Which of the following in not the part of structures of the olfactory system? (a) Nose (b) Nasal cavity (c) Olfactory bulbs (d) Mouth 5. Which of the following is located in the nose contains millions of chemical receptors that detect odors? (a) Olfactory epithelium (b) Nasal cavity (c) Olfactory bulbs (d) Mouth Answers: 1. (a), 2. (a), 3. (d), 4. (d), 5. (a) 4.10 References References of this unit have been given at the end of the book.  CU IDOL SELF LEARNING MATERIAL (SLM)

128 Experimental Psychology UNIT 5 SENSORY PROCESSES: STRUCTURE AND FUNCTION OF GUSTATORYAND KINESTHETIC Structure: 5.0 Learning Objectives 5.1 Introduction 5.2 Gustatory 5.3 Functional Structure 5.4 Structure and Function of Gustatory 5.5 Structure and Function of Kinesthetic 5.6 What Does Kinesthesis Do? 5.7 Kinesthesis and Learning Styles 5.8 Summary 5.9 Key words/Abbreviations 5.10 LearningActivity 5.11 Unit End Exercises (MCQs and Descriptive) 5.12 References 5.0 Learning Objectives After studying this unit, you will be able to:  Explain the sensory processes of Gustatory and Kinesthetic  Discuss kinesthesis and learning styles CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Gustatory and Kinesthetic 129 5.1 Introduction The gustatory system is the sensory system responsible for the perception of taste and flavour. In humans, the gustatory system is comprised of taste cells in the mouth (which sense the five taste modalities: salty, sweet, bitter, sour and umami), several cranial nerves, and the gustatory cortex. Taste, or gustation, is a sense that develops through the interaction of dissolved molecules with taste buds. Currently, five sub-modalities (tastes) are recognized, including sweet, salty, bitter, sour and umami (savory taste or the taste of protein). Taste is associated mainly with the tongue, although there are taste (gustatory) receptors on the palate and epiglottis as well. The surface of the tongue, along with the rest of the oral cavity, is lined by a stratified squamous epithelium. In the surface of the tongue are raised bumps, called papilla, that contain the taste buds. There are three types of papilla, based on their appearance: vallate, foliate and fungiform. 5.2 Gustatory Taste, gustatory perception or gustation (Adjectival form: gustatory) is one of the five traditional senses that belongs to the gustatory system. Taste is the sensation produced or stimulated when a substance in the mouth reacts chemically with taste receptor cells located on taste buds in the oral cavity, mostly on the tongue. Taste, along with smell (olfaction) and trigeminal nerve stimulation (registering texture, pain and temperature), determines flavors of food and/or other substances. Humans have taste receptors on taste buds (gustatory calyculi) and other areas including the upper surface of the tongue and the epiglottis. The gustatory cortex is responsible for the perception of taste. The tongue is covered with thousands of small bumps called papillae, which are visible to the naked eye. Within each papilla are hundreds of taste buds. The exception to this is the filiform papillae that do not contain taste buds. There are between 2000 and 5000 taste buds that are located on the back and front of the tongue. Others are located on the roof, sides and back of the mouth, and in the throat. Each taste bud contains 50 to 100 taste receptor cells. The sensation of taste includes five established basic tastes: sweetness, sourness, saltiness, bitterness and umami. Scientific experiments have demonstrated that these five tastes exist and are distinct from one another. Taste buds are able to distinguish between different tastes through detecting CU IDOL SELF LEARNING MATERIAL (SLM)

130 Experimental Psychology interaction with different molecules or ions. Sweet, savory and bitter tastes are triggered by the binding of molecules to G protein-coupled receptors on the cell membranes of taste buds. Saltiness and sourness are perceived when alkali metal or hydrogen ions enter taste buds, respectively. Papillae = taste buds Epiglottis Palatine tonsil Lingual tonsil Circumvallate papilla Fungiform (b) Taste bud (a) paillae Fig. 5.1: Gustatory The basic tastes contribute only partially to the sensation and flavor of food in the mouth other factors include smell, detected by the olfactory epithelium of the nose; texture, detected through a variety of mechanoreceptors, muscle nerves, etc.; temperature, detected by thermoreceptors; and “coolness” (such as of menthol) and “hotness” (pungency), through chemesthesis. As taste senses both harmful and beneficial things, all basic tastes are classified as either aversive or appetitive, depending upon the effect the things they sense have on our bodies. Sweetness helps to identify energy-rich foods, while bitterness serves as a warning sign of poisons. Among humans, taste perception begins to fade around 50 years of age because of loss of tongue papillae and a general decrease in saliva production. Humans can also have distortion of tastes through dysgeusia. Not all mammals share the same taste senses: some rodents can taste CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Gustatory and Kinesthetic 131 starch (which humans cannot), cats cannot taste sweetness, and several other carnivores including hyenas, dolphins and sea lions, have lost the ability to sense up to four of their ancestral five taste senses. 5.3 Functional Structure Taste Buds and Papillae of the Tongue In the human body, a stimulus refers to a form of energy which elicits a physiological or psychological action or response. Sensory receptors are the structures in the body which change the stimulus from one form of energy to another. This can mean changing the presence of a chemical, sound wave, source of heat, or touch to the skin into an electrical action potential which can be understood by the brain, the body’s control center. Sensory receptors are modified ends of sensory neurons; modified to deal with specific types of stimulus, thus there are many different types of sensory receptors in the body. The neuron is the primary component of the nervous system, which transmits messages from sensory receptors all over the body. Taste is a form of chemoreception which occurs in the specialised taste receptors in the mouth. To date, there are five different types of taste these receptors can detect which are recognized: salt, sweet, sour, bitter and umami. Each type of receptor has a different manner of sensory transduction: that is, of detecting the presence of a certain compound and starting an action potential which alerts the brain. It is a matter of debate whether each taste cell is tuned to one specific tastant or to several; Smith and Margolskee claim that “gustatory neurons typically respond to more than one kind of stimulus, although each neuron responds most strongly to one tastant”. Researchers believe that the brain interprets complex tastes by examining patterns from a large set of neuron responses. This enables the body to make “keep or spit out” decisions when there is more than one tastant present. “No single neuron type alone is capable of discriminating among stimuli or different qualities, because a given cell can respond the same way to disparate stimuli.” As well, serotonin is thought to act as an intermediary hormone which communicates with taste cells within a taste bud, mediating the signals being sent to the brain. Receptor molecules are found on the top of microvilli of the taste cells. CU IDOL SELF LEARNING MATERIAL (SLM)

132 Experimental Psychology Sweetness Sweetness is produced by the presence of sugars, some proteins, and other substances such as alcohols like anethol, glycerol and propylene glycol, saponins such as glycyrrhizin, artificial sweeteners (organic compounds with a variety of structures) and lead compounds such as lead acetate. It is often connected to aldehydes and ketones, which contain a carbonyl group. Many foods can be perceived as sweet despite of the sugar content, alcoholic drinks can taste sweet despite of having sugar or not, some plants such as liquorice, anise or stevia are sometimes used as sweeteners. Rebaudioside A is a steviol glycoside coming from stevia that is 200 times sweeter than sugar. Lead acetate and other lead compounds were used as sweeteners, mostly for wine, until lead poisoning became known. Romans used to deliberately boil the must inside of lead vessels to make a sweeter wine. Sweetness is detected by a variety of G protein-coupled receptors coupled to a G protein that acts as an intermediary in the communication between taste bud and brain, gustducin. These receptors are T1R2+3 (heterodimer) and T1R3 (homodimer), which account for sweet sensing in humans and other animals. Sourness Sourness is acidity, and, like salt, it is a taste sensed using ion channels. Undissociated acid diffuses across the plasma membrane of a presynaptic cell, where it dissociates in accordance with Le Chatelier’s principle. The protons that are released then block potassium channels, which depolarise the cell and cause calcium influx. In addition, the taste receptor PKD2L1 has been found to be involved in tasting sour. Bitterness Research has shown that TAS2Rs (taste receptors, type 2, also known as T2Rs) such as TAS2R38 are responsible for the human ability to taste bitter substances. They are identified not only by their ability to taste certain bitter ligands, but also by the morphology of the receptor itself (surface bound, monomeric). Savoriness The amino acid glutamic acid is responsible for savoriness, but some nucleotides (inosinic acid and guanylic acid) can act as complements, enhancing the taste. Glutamic acid binds to a variant of the G protein-coupled receptor, producing a savory taste. CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Gustatory and Kinesthetic 133 Further Sensations and Transmission The tongue can also feel other sensations not generally included in the basic tastes. These are largely detected by the somatosensory system. In humans, the sense of taste is conveyed via three of the twelve cranial nerves. The facial nerve (VII) carries taste sensations from the anterior two thirds of the tongue; the glossopharyngeal nerve (IX) carries taste sensations from the posterior one third of the tongue while a branch of the vagus nerve (X) carries some taste sensations from the back of the oral cavity. The trigeminal nerve (cranial nerve V) provides information concerning the general texture of food as well as the taste-related sensations of peppery or hot (from spices). Pungency Substances such as ethanol and capsaicin cause a burning sensation by inducing a trigeminal nerve reaction together with normal taste reception. The sensation of heat is caused by the food’s activating nerves that express TRPV1 and TRPA1 receptors. Some such plant-derived compounds that provide this sensation are capsaicin from chili peppers, piperine from black pepper, gingerol from ginger root and allyl isothiocyanate from horseradish. The piquant (“hot” or ‘spicy”) sensation provided by such foods and spices plays an important role in a diverse range of cuisines across the world especially in equatorial and sub-tropical climates, such as Ethiopian, Peruvian, Hungarian, Indian, Korean, Indonesian, Lao, Malaysian, Mexican, New Mexican, Singaporean, Southwest Chinese (including Szechuan cuisine), Vietnamese and Thai cuisines. This particular sensation, called chemesthesis, is not a taste in the technical sense, because the sensation does not arise from taste buds, and a different set of nerve fibers carry it to the brain. Foods like chili peppers activate nerve fibers directly; the sensation interpreted as “hot” results from the stimulation of somatosensory (pain/temperature) fibers on the tongue. Many parts of the body with exposed membranes but no taste sensors (such as the nasal cavity, under the fingernails, surface of the eye or a wound) produce a similar sensation of heat when exposed to hotness agents. Asian countries within the sphere of, mainly, Chinese, Indian, and Japanese cultural influence, often wrote of pungency as a fifth or sixth taste. CU IDOL SELF LEARNING MATERIAL (SLM)

134 Experimental Psychology Coolness Some substances activate cold trigeminal receptors even when not at low temperatures. This “fresh” or “minty’ sensation can be tasted in peppermint, spearmint, menthol, anethol, ethanol, and camphor. Caused by activation of the same mechanism that signals cold, TRPM8 ion channels on nerve cells, unlike the actual change in temperature described for sugar substitutes, this coolness is only a perceived phenomenon. Numbness Both Chinese and Batak Toba cooking include the idea of, a tingling numbness caused by spices such as Sichuan pepper. The cuisines of Sichuan province in China and of the Indonesian province of North Sumatra often combine this with chili pepper to produce, “numbing-and-hot”, or “mati rasa” flavor. These sensations although not taste fall into a category of chemesthesis. Astringency Some foods, such as unripe fruits, contain tannins or calcium oxalate that cause an astringent or puckering sensation of the mucous membrane of the mouth. Examples include tea, red wine, rhubarb, some fruits of the genus Syzygium, and unripe persimmons and bananas. When referring to wine, dry is the opposite of sweet, and does not refer to astringency. Wines that contain tannins and so cause an astringent sensation are not necessarily classified as “dry”, and “dry” wines are not necessarily astringent. Metallicness A metallic taste may be caused by food and drink, certain medicines or amalgam dental fillings. It is generally considered an off flavor when present in food and drink. A metallic taste may be caused by galvanic reactions in the mouth. In the case where it is caused by dental work, the dissimilar metals used may produce a measurable current. Some artificial sweeteners are perceived to have a metallic taste, which is detected by the TRPV1 receptors. Many people consider blood to have a metallic taste. A metallic taste in the mouth is also a symptom of various medical conditions, in which case it may be classified under the symptoms dysgeusia or parageusia, referring to distortions of the sense of taste, and can be caused by various kinds of medication, including saquinavir and zonisamide, and occupational hazards, such as working with pesticides. CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Gustatory and Kinesthetic 135 Calcium The distinctive taste of chalk has been identified as the calcium component of that substance. In 2008, geneticists discovered a CaSR calcium receptor on the tongues of mice. The CaSR receptor is commonly found in the gastrointestinal tract, kidneys, and brain. Along with the “sweet” T1R3 receptor, the CaSR receptor can detect calcium as a taste. Whether the perception exists or not in humans is unknown. Fat Taste Recent research reveals a potential taste receptor called the CD36 receptor. CD36 was targeted as a possible lipid taste receptor because it binds to fat molecules (more specifically, long-chain fatty acids) and it has been localized to taste bud cells (specifically, the circumvallate and foliate papillae). There is a debate over whether we can truly taste fats, and supporters of our ability to taste free fatty acids (FFAs) have based the argument on a few main points: there is an evolutionary advantage to oral fat detection; a potential fat receptor has been located on taste bud cells; fatty acids evoke specific responses that activate gustatory neurons, similar to other currently accepted tastes; and, there is a physiological response to the presence of oral fat. Although CD36 has been studied primarily in mice, research examining human subjects’ ability to taste fats found that those with high levels of CD36 expression were more sensitive to tasting fat than were those with low levels of CD36 expression; this study points to a clear association between CD36 receptor quantity and the ability to taste fat. Other possible fat taste receptors have been identified. G protein-coupled receptors GPR120 and GPR40 have been linked to fat taste, because their absence resulted in reduced preference to two types of fatty acid (linoleic acid and oleic acid), as well as decreased neuronal response to oral fatty acids. Monovalent cation channel TRPM5 has been implicated in fat taste as well, but it is thought to be involved primarily in downstream processing of the taste rather than primary reception, as it is with other tastes such as bitter, sweet and savory. Proposed alternate names to fat taste include oleogustus and pinguis, although these terms are not widely accepted. The main form of fat that is commonly ingested is triglycerides, which are CU IDOL SELF LEARNING MATERIAL (SLM)

136 Experimental Psychology composed of three fatty acids bound together. In this state, triglycerides are able to give fatty foods unique textures that are often described as creaminess. But this texture is not an actual taste. It is only during ingestion that the fatty acids that make up triglycerides are hydrolyzed into fatty acids via lipases. The taste is commonly related to other, more negative, tastes such as bitter and sour due to how unpleasant the taste is for humans. Richard Mattes, a co-author of the study, explained that low concentrations of these fatty acids can create an overall better flavor in a food, much like how small uses of bitterness can make certain foods more rounded. However, a high concentration of fatty acids in certain foods is generally considered inedible. To demonstrate that individuals can distinguish fat taste from other tastes, the researchers separated volunteers into groups and had them try samples that also contained the other basic tastes. Volunteers were able to separate the taste of fatty acids into their own category, with some overlap with savory samples, which the researchers hypothesized was due to poor familiarity with both. The researchers note that the usual “creaminess and viscosity we associate with fatty foods is largely due to triglycerides”, unrelated to the taste; while the actual taste of fatty acids is not pleasant. Mattes described the taste as “more of a warning system” that a certain food should not be eaten. There are few regularly consumed foods rich in fat taste, due to the negative flavor that is evoked in large quantities. Foods whose flavor to which fat taste makes a small contribution include olive oil and fresh butter, along with various kinds of vegetable and nut oils. Heartiness Kokumi is translated as “heartiness” or “full flavor” and describes compounds in food that do not have their own taste, but enhance the characteristics when combined. There are four basic tastes: sweet, sour, salt and bitter. Two additional tastes for some people are umami (which enhances the original four and has been described as fatty or “deliciousness” associated with Asian foods), and kokumi which may enhance the other five tastes by magnifying and lengthening the other tastes. This sensation has also been described as “mouthfulness”. Garlic is a common ingredient to add flavor used to help define the characteristic kokumi flavors. Calcium-sensing receptors (CaSR) are receptors for “kokumi” substances. Kokumi substances, applied around taste pores, induce an increase in the intracellular Ca concentration in a subset of CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Gustatory and Kinesthetic 137 cells. This subset of CaSR-expressing taste cells are independent from the influenced basic taste receptor cells. CaSR agonists directly activate the CaSR on the surface of taste cells and integrated in the brain via the central nervous system. However, a basal level of calcium, corresponding to the physiological concentration, is necessary for activation of the CaSR to develop the kokumi sensation. Temperature Temperature can be an essential element of the taste experience. Heat can accentuate some flavors and decrease others by varying the density and fase equilibrium of a substance. Food and drink that in a given culture is traditionally served hot is often considered distasteful if cold, and vice versa. For example, alcoholic beverages, with a few exceptions, are usually thought best when served at room temperature or chilled to varying degrees, but soups again, with exceptions are usually only eaten hot. A cultural example is soft drinks. In North America, it is almost always preferred cold, regardless of season. Starchiness A 2016 study suggested that humans can taste starch (specifically, a glucose oligomer) independently of other tastes such as sweetness. However, no specific chemical receptor has yet been found for this taste. 5.4 Structure and Function of Gustatory The gustatory cortex is located in cerebral cortex, which is the outer part of the brain. The gustatory cortex is made up of two small substructures that are found in two different lobes of the brain. These substructures are the anterior insula, located on the insular lobe, and the frontal operculum, on the frontal lobe. The insular lobe is found deep within the cerebral cortex, located under the frontal, parietal and temporal lobes. The frontal lobe is located at the front of the brain, directly behind the forehead. CU IDOL SELF LEARNING MATERIAL (SLM)

138 Experimental Psychology Fig. 5.2: Function of Gustatory The gustatory cortex functions to give a person the perception of taste. The gustatory cortex works with the taste buds to create the taste sensation. The tongue is covered with taste buds, and taste buds in different areas of the tongue sense different types of flavors. For example, the taste buds for sweet tastes are located mostly near the tip of the tongue, while taste buds for bitter tastes are located near the back of the tongue. There are a total of five different types of flavors or tastes such as sweet, salty, bitter, sour, savory or umani. 5.5 Structure and Function of Kinesthetic Kinesthetic handwriting training takes the drudgery out of a task that is often difficult and time- consuming. For all children and for their teachers, this provides some benefit. For some children, kinesthetic training is the single most effective tool for learning handwriting. Children who benefit the most from kinesthetic handwriting training usually have identifiable problems in one or more general areas. Developmental gross and fine motor foundation skills for cursive instruction may be less than optimal. Output or production problems may include difficulties with visual motor control. Kinesthesia is the key to the lost science of handwriting. Properly understood, it is the basis for understanding handwriting problems and for preventing or remediating them. Kinesthesia can be a CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Gustatory and Kinesthetic 139 curse or a blessing. When a complex motor activity is scientifically analyzed, appropriate foundation skills are set, teaching steps are properly sequenced, and the skill is practiced to the automatic level of performance, kinesthesia is a lifelong blessing in the performance of that skill. On the other hand, maladaptive kinesthetic patterns can be a curse. When a motor activity is haphazardly acquired at an immature stage of development and reinforced to the automatic level of performance, the kinesthetic pattern can last a lifetime, blocking effective and efficient performance of the skill and frustrating any attempts to modify it. Fig. 5.3: Function of Kinesthetic Kinesthesis refers to sensory input that occurs within the body. Postural and movement information are communicated via sensory systems by tension and compression of muscles in the body. Even when the body remains stationary, the kinesthetic sense can monitor its position. Humans possess three specialized types of neurons responsive to touch and stretching that help keep track of body movement and position. The first class, called Pacinian corpuscles, lies in the deep subcutaneous CU IDOL SELF LEARNING MATERIAL (SLM)

140 Experimental Psychology fatty tissue and responds to pressure. The second class of neurons surrounds the internal organs, and the third class is associated with muscles, tendons and joints. These neurons work in concert with one another and with cortical neurons as the body moves. The ability to assess the weight of an object is another function of kinesthesia. When an individual picks up an object, the tension in his/her muscles generates signals that are used to adjust posture. This sense does not operate in isolation from other senses. For example, the size-weight illusion results in a mismatch between how heavy an object looks and how heavy the muscles “think” it should be. In general, larger objects are judged as being heavier than smaller objects of the same weight. The kinesthetic sense does not mediate equilibrium, or sense of balance. Balance involves different sensory pathways and originates in large part within the inner ear. Kinesthesis also referred to as kinesthesia, is the perception of body movements. It involves being able to detect changes in body position and movements without relying on information from the five senses. You are using your kinesthetic sense whenever you are involved in a physical activity such as walking, running, driving, dancing, swimming, and anything that requires body movement. 5.6 What Does Kinesthesis Do? Through your sense of kinesthesis, you can tell where different parts of your body are located even if your eyes are closed or you are standing in a dark room. For example, when you are riding a bicycle, receptors in your arms and legs send information to the brain about the position and movement of your limbs. When you think of the five major senses (vision, smell, touch, taste and hearing), you might note that these all tend to focus on perceiving stimuli outside of the self. Kinesthesis is one type of sense that is focused on the body’s internal events. Rather than using this sense to detect stimuli outside of the self, your sense of kinesthesis allows you to know where your body is positioned and to detect changes in body position. When you need to perform a complex physical action, your sense of kinesthesis allows you to know where your body is and how much further it needs to go. CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Gustatory and Kinesthetic 141 5.7 Kinesthesis and Learning Styles Kinesthesis relates to one of the three major learning styles in Fleming VAK model. According to the theories of learning styles, people learn best if the instruction is offered according to their learning preferences. An individual with a kinesthetic learning style would learn best by doing, or actually performing an action. Imagine, for example, that you are trying to learn how to hit a baseball with a bat. If you have a kinesthetic learning style, you might learn best by actually performing the action. Instead of just reading about how to hit a ball or watching other people perform this action, you need to actually get a bat in your hands and practice swinging the bat at a ball. Kinesthetic learners are thought to enjoy being physically active, tend to excel at sports and often have fast reaction times. The VAK/VARK model of learning suggests that people with this learning style may prefer lessons that involve movement such as performing an experiment, working with a group or performing a skit. While the concept of learning styles is enormously popular, particularly in the field of education, most research has found that there is little evidence supporting the idea that instructing students according to their preferred learning style has any difference on educational outcomes. However, if you are a person who prefers learning by doing, as kinesthetic learners often do, you can perhaps take advantage of this knowledge when you are trying to learn something new. Rather than bore yourself with reading instruction manuals or listening to lectures, look for ways that you can gain hands-on experience. 5.8 Summary The gustatory system is the sensory system responsible for the perception of taste and flavour. In humans, the gustatory system is comprised of taste cells in the mouth (which sense the five taste modalities: salty, sweet, bitter, sour and umami), several cranial nerves and the gustatory cortex. Taste, or gustation, is a sense that develops through the interaction of dissolved molecules with taste buds. Currently five sub-modalities (tastes) are recognized, including sweet, salty, bitter, sour and umami (savory taste or the taste of protein). Taste is associated mainly with the tongue, although there are taste (gustatory) receptors on the palate and epiglottis as well. The surface of the tongue, CU IDOL SELF LEARNING MATERIAL (SLM)

142 Experimental Psychology along with the rest of the oral cavity, is lined by a stratified squamous epithelium. In the surface of the tongue are raised bumps, called papilla, that contain the taste buds. Taste, gustatory perception, or gustation is one of the five traditional senses that belongs to the gustatory system. Taste is the sensation produced or stimulated when a substance in the mouth reacts chemically with taste receptor cells located on taste buds in the oral cavity, mostly on the tongue. Taste, along with smell (olfaction) and trigeminal nerve stimulation (registering texture, pain and temperature), determines flavors of food and/or other substances. Humans have taste receptors on taste buds and other areas including the upper surface of the tongue and the epiglottis. The gustatory cortex is responsible for the perception of taste. The sensation of taste includes five established basic tastes: sweetness, sourness, saltiness, bitterness and umami. Scientific experiments have demonstrated that these five tastes exist and are distinct from one another. Taste buds are able to distinguish between different tastes through detecting interaction with different molecules or ions. Sweet, savory and bitter tastes are triggered by the binding of molecules to G protein-coupled receptors on the cell membranes of taste buds. Saltiness and sourness are perceived when alkali metal or hydrogen ions enter taste buds, respectively. In the human body, a stimulus refers to a form of energy which elicits a physiological or psychological action or response. Sensory receptors are the structures in the body which change the stimulus from one form of energy to another. This can mean changing the presence of a chemical, sound wave, source of heat, or touch to the skin into an electrical action potential which can be understood by the brain, the body’s control center. Sensory receptors are modified ends of sensory neurons; modified to deal with specific types of stimulus, thus there are many different types of sensory receptors in the body. The neuron is the primary component of the nervous system, which transmits messages from sensory receptors all over the body. Taste is a form of chemoreception which occurs in the specialised taste receptors in the mouth. To date, there are five different types of taste these receptors can detect which are recognized: salt, sweet, sour, bitter and umami. Each type of receptor has a different manner of sensory transduction: that is, of detecting the presence of a certain compound and starting an action potential which alerts the brain. It is a matter of debate whether each taste cell is tuned to one specific tastant or to several; Smith and Margolskee claim that “gustatory neurons typically respond to more than one kind of stimulus, although each neuron responds most strongly to one tastant”. Researchers believe that the brain interprets complex tastes by examining patterns from a large set of neuron responses. CU IDOL SELF LEARNING MATERIAL (SLM)

Sensory Processes: Structure and Function of Gustatory and Kinesthetic 143 This enables the body to make “keep or spit out” decisions when there is more than one tastant present. “No single neuron type alone is capable of discriminating among stimuli or different qualities, because a given cell can respond the same way to disparate stimuli.” As well, serotonin is thought to act as an intermediary hormone which communicates with taste cells within a taste bud, mediating the signals being sent to the brain. Receptor molecules are found on the top of microvilli of the taste cells. Sweetness is produced by the presence of sugars, some proteins, and other substances such as alcohols like anethol, glycerol and propylene glycol, saponins such as glycyrrhizin, artificial sweeteners (organic compounds with a variety of structures), and lead compounds such as lead acetate. It is often connected to aldehydes and ketones, which contain a carbonyl group. Many foods can be perceived as sweet despite of the sugar content, alcoholic drinks can taste sweet despite of having sugar or not, some plants such as liquorice, anise or stevia are sometimes used as sweeteners. Sourness is acidity, and, like salt, it is a taste sensed using ion channels. Undissociated acid diffuses across the plasma membrane of a presynaptic cell, where it dissociates in accordance with Le Chatelier’s principle. The protons that are released then block potassium channels, which depolarise the cell and cause calcium influx. In addition, the taste receptor PKD2L1 has been found to be involved in tasting sour. The tongue can also feel other sensations not generally included in the basic tastes. These are largely detected by the somatosensory system. In humans, the sense of taste is conveyed via three of the twelve cranial nerves. The facial nerve (VII) carries taste sensations from the anterior two thirds of the tongue; the glossopharyngeal nerve (IX) carries taste sensations from the posterior one third of the tongue while a branch of the vagus nerve (X) carries some taste sensations from the back of the oral cavity. The gustatory cortex is located in cerebral cortex, which is the outer part of the brain. The gustatory cortex is made up of two small substructures that are found in two different lobes of the brain. These substructures are the anterior insula, located on the insular lobe, and the frontal operculum, on the frontal lobe. The insular lobe is found deep within the cerebral cortex, located under the frontal, parietal and temporal lobes. The frontal lobe is located at the front of the brain, directly behind the forehead. The gustatory cortex functions to give a person the perception of taste. The gustatory cortex works with the taste buds to create the taste sensation. The tongue is covered with taste buds, and CU IDOL SELF LEARNING MATERIAL (SLM)

144 Experimental Psychology taste buds in different areas of the tongue sense different types of flavors. For example, the taste buds for sweet tastes are located mostly near the tip of the tongue, while taste buds for bitter tastes are located near the back of the tongue. There are a total of five different types of flavors or tastes such as sweet, salty, bitter, sour, savory or umani. Kinesthetic handwriting training takes the drudgery out of a task that is often difficult and time- consuming. For all children and for their teachers, this provides some benefit. For some children, kinesthetic training is the single most effective tool for learning handwriting. Children who benefit the most from kinesthetic handwriting training usually have identifiable problems in one or more general areas. Developmental gross and fine motor foundation skills for cursive instruction may be less than optimal. Output or production problems may include difficulties with visual motor control. Kinesthesia is the key to the lost science of handwriting. Properly understood, it is the basis for understanding handwriting problems and for preventing or remediating them. Kinesthesia can be a curse or a blessing. When a complex motor activity is scientifically analyzed, appropriate foundation skills are set, teaching steps are properly sequenced, and the skill is practiced to the automatic level of performance, kinesthesia is a lifelong blessing in the performance of that skill. On the other hand, maladaptive kinesthetic patterns can be a curse. When a motor activity is haphazardly acquired at an immature stage of development and reinforced to the automatic level of performance, the kinesthetic pattern can last a lifetime, blocking effective and efficient performance of the skill and frustrating any attempts to modify it. Kinesthesis refers to sensory input that occurs within the body. Postural and movement information are communicated via sensory systems by tension and compression of muscles in the body. Even when the body remains stationary, the kinesthetic sense can monitor its position. Humans possess three specialized types of neurons responsive to touch and stretching that help keep track of body movement and position. The first class, called Pacinian corpuscles, lies in the deep subcutaneous fatty tissue and responds to pressure. The second class of neurons surrounds the internal organs, and the third class is associated with muscles, tendons, and joints. These neurons work in concert with one another and with cortical neurons as the body moves. The ability to assess the weight of an object is another function of kinesthesia. When an individual picks up an object, the tension in his/her muscles generates signals that are used to adjust posture. This sense does not operate in isolation from other senses. For example, the size-weight CU IDOL SELF LEARNING MATERIAL (SLM)