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Western University
Psychology 1000
Terry Biggs

Psychology Chapter 5 Notes Synesthesia: ‘mixing of the senses’; these people may experience sounds as colours or tastes as touch sensations that have different shapes; women are more likely to be synaesthetes than men; it is suggested that all humans may be born synaesthetic Transduction: sensory receptors translate information from stimuli (senses) into nerve impulses Feature Detectors: specialized neurons that break down and analyze the specific features of the stimuli; these pieces are then reconstructed into a neural representation that is then compared with previously stored information, such as our knowledge of what particular objects look, smell or feel like; this allows us to recognize the stimulus and give it meaning- we consciously experience a perception  Theories for Synesthesia:  1. The pruning of neural connections that occurs in infancy has not occurred in people with synesthesia, so that brain regions retain connections that are absent in most people- Support: diffusion tensor imagining, which lights up white matter pathways in the brain, has revealed increased connectivity in patients with synesthesia  2. With synesthesia, there is a deficit in neural inhibitory processes in the brain that ordinarily keep input from one sensory modality from ‘overflowing’ into other sensory areas and stimulating them Binding Problem: mystery in cognitive neuroscience: how do we bind all our perceptions into one complete whole while keeping its sensory elements separate? Sensation: stimulus-detection process by which our sense organs respond to and translate environmental stimuli into nerve impulses that are sent to the brain Perception: making ‘sense’ of what our senses tell us- the active process of organizing this stimulus input and giving it meaning Sensory Processes  The sensory equipment of any species is an adaptation to the environment in which it lives Transduction: the process whereby the characteristics of a stimulus are converted into nerve impulses; this relates to the range of stimuli to which humans and other mammals are attuned and the manner in which the various sense organs carry out the transduction process  Human sensory systems are designed to extract from the environment the information that we need to function and survive Psychophysics: scientific area which studies relations between the physical characteristics of stimuli and sensory capabilities and is concerned with two kinds of sensitivity; the first concerns the absolute limits of sensitivity (softest sound/weakest salt detection), and the second has to do with differences between stimuli (between brightness or between two tones) Stimulus Detection: the Absolute Threshold Absolute threshold: the lowest intensity at which a stimulus can be detected correctly 50% of the time; the lower the absolute threshold, the greater the sensitivity Signal Detection Theory  Psychologists have found that people’s apparent sensitivity can fluctuate quite a bit; they concluded that the concept of a fixed absolute threshold is inaccurate because there is no single point on the intensity sale that separates nondetection from detection of a stimulus Decision criterion: a standard of how certain they must be that a stimulus is present before they will say they detect it; it can also change from time to time, depending on such factors as fatigue, expectation, and the potential significance of the stimulus Signal detection theory: concerned with the factors that influence sensory judgments; participants of a signal-detection test will become more conservative in their ‘yes’ responses as costs for false alarms are increased, resulting in higher detection thresholds The Difference Threshold Difference threshold: the smallest difference between two stimuli that people can perceive 50% of the time; sometimes called the just noticeable difference  Ernst Weber: German physiologist who discovered in the 1830s that there is some degree of lawfulness in the range of sensitivities within our sensory systems Weber’s Law: the difference threshold, or jnd, is directly proportional to the magnitude of the stimulus with which the comparison is being made, and can be expressed as a Weber fraction; although Weber’s law breaks down at extremely high and low intensities of stimulation, it holds up reasonable well within the most frequently encountered range, therefore providing a reasonable barometer of our abilities to discern differences in the various sensory modalities; the smaller the fraction, the greater the sensitivity to differences Sensory Adaptation Sensory adaptation: sensory neurons are engineered to respond to a constant stimulus by decreasing their activity, and diminishing sensitivity to an unchanging stimulus; adaptation is sometimes called habituation  Although sensory adaptation may reduce our overall sensitivity, it is adaptive because it frees our senses from the constant and the mundane to pick up informative changes in the environment; such changes may turn out to be important to our well-being or survival The Sensory Systems Vision  The normal stimulus for vision is electromagnetic energy, or light waves which are measured in nanometres (400-700nm).  Light waves enter the eye through the cornea, a transparent protective structure at the front of the pupil, an adjustable opening that can dilate or constrict to control the amount of light that enters the eye o The pupil’s size is controlled by muscles in the coloured iris that surrounds the puil; low levels of illumination cause the pupil to dilate, letting more light into the eye to improve optical clarity; bright light triggers constriction  Behind the pupil is the lens, an elastic structure that becomes thinner to focus on distant objects and thicker to focus on nearby objects; the lens focuses the visual image on the light-sensitive retina, a multilayered tissue at the rear of the fluid-filled eyeball.  The lens reverses the image from right to left and top to bottom when it is projected on the retina, but the brain reconstructs the visual input into the image that we perceive Myopia: nearsightedness; the lens focuses the visual image in front of the retina (too near the lens), resulting in a blurred image for faraway objects. This generally occurs because the eyeball is longer than normal Hyperopia: farsightedness; occurs when the lens does not thicken enough and the image is therefore focused on a point behind the retina. The aging process typically causes the eyeball to become shorter over time, contributing to the development of hyperopia- this also often improves the vision of myopic people, for, as the retina moves closer to the lens, it approaches the point where the ‘nearsightedness’ lens is projecting the right image  The retina is actually an extension of the brain, and contains two types of light-sensitive receptor cells called rods and cones; there are about 120 million rods and 6 million cones in the human eye Rods: function best in dim light, are primarily black-and-white brightness receptors; 500 times more sensitive to light than cones, but they do not give rise to colour sensations Cones: colour receptors and function best in bright illumination  Rods are found throughout the retina except in the fovea, a small area in the centre of the retina that contains only cones. Cones decrease in concentration as one moves away from the centre of the retina, and the periphery of the retina contains mainly rods Bipolar cells: have synaptic connections with the rods and cones; the bipolar cells, in turn, synapse with a layer of about one million ganglion cells, whose axons are collected into a bundle to form the optic nerve.  The rods and cones not only form the rear layer of the retina, but their light-sensitive ends actually point away from the direction of the entering light so that they receive only a fraction of the light energy that enters the eye  Many rods are connected to the same bipolar cell and therefore can combine their individual electrical messages to the bipolar cell, where the additive effect of the may signals may be enough to fire it Visual acuity: ability to see fine detail  The cones that lie in the periphery of the retina also share bipolar cells. In the fovea however, the densely packed cones each have their own single bipolar cell, which is why our visual acuity is greatest when the visual image projects directly onto the fovea  The optic nerve formed by the axons of the ganglion cell exits through the back o the eye not far from the fovea, producing a blind spot, where there are no photoreceptors Photopigments: protein molecules used by rods and cones to translate light waves into nerve impulses; the absorption of light by these molecules produces a chemical reaction that changes the rate of neurotransmitter release at the receptor’s synapse with the bipolar cells  If nerve responses are triggered at each of the three levels (rod or cone, bipolar cell, and ganglion cell), the message is instantaneously on its way to the visual relay station in the thalamus, and then on to the visual cortex of the brain  Research has shown that rods have much greater brightness sensitivity than cones throughout the colour spectrum except at the red end, where rods are relatively insensitive; Dark adaptation: the progressive improvement in brightness sensitivity tat occurs over time under conditions of low illumination; after absorbing light, a photoreceptor is depleted of its pigment molecules for a period of time. If the eye has been exposed to conditions of high illumination, a substantial amount of photopigment will be depleted, which is why during the process of dark adaptation, the photopigment molecules are regenerated, and the receptor’s sensitivity increases greatly  It is estimated that after complete adaptation, rods are able to detect light intensities only 1/10,000 as great as those that could be detected before dark adaptation began  Our difference thresholds for light wavelengths are so small that we are able to distinguish an estimated 7.5 million hue variations; there are two different historical theories of colour vision that have tried to explain this: o The Trichromatic Theory: there are three types of colour receptors in the retina: although all cones can be stimulated by most wavelengths to varying degrees, individual cones are most sensitive to wavelengths that correspond to either blue, green, or red; if all three cones are equally activated, a pure white colour is perceived; this did not explain why red-green colour blindness are able to experience yellow if, according to the theory, yellow is produced by activity of red and green receptors. A second phenomenon that posed problems was the colour afterimage, in which an image in a different colour appears after a colour stimulus has been viewed steadily and then withdrawn o Opponent-Process Theory: each of the three cone types responds to two different wavelengths; one type is red or green, another to blue or yellow, and a third to black or white o Dual Process Theory: combines the two; the cones do contain one of three different protein photopigments that are most sensitive to wavelengths corresponding to blue, red and green. Different ratios of activity in the red-, blue- and green- sensitive cones can produce a pattern of neural activity that corresponds to any hue in the spectrum; as well, certain ganglion cells in the retina, as well as some neurons in visual relay stations and the visual cortex, respond in an opponent-process fashion by altering their rate of firing  People with normal colour vision are referred to as trichromats. About 7% of the male population and 1% of the female population have a deficiency in the red-green system, the yellow-blue system, or both. A dichromat is a person who is colour-blind in only one of the systems; A monochromat is sensitive only to the black-white system and is totally colour-blind Primary visual cortex: in the occipital lobe at the rear of the brain: the input from the visual relay station in the thalamus is routed here in particular  The fovea, where the one-to-one synapses of cones with bipolar cells produces high visual acuity, is represented by a disproportionately large area of the visual cortex  There is also more than one cortical ‘map’ of the retina; there are at least 10 duplicate mappings Feature detectors: fire selectively in response to stimuli that have specific characteristics; using tiny electrodes to record the activity of individual cells of the visual cortex of animals, David Hubel and Torsten Wiesel found that certain neurons fired most frequently when lines of certain orientations were presented. Since this discovery, scientists have found cells that respond most strongly to bars, slits, and edges in certain positions; within the cortex, this information is integrated and analyzed by successively more complex feature detector systems Parallel processing: the brain simultaneously analyzes colours, shapes, distances, and movement, constructing a unified image of its properties Visual association cortex: successively more complex features of the visual scene are combined and interpreted in light of our memories and knowledge  Neurons in the brain respond selectively not only to basic stimulus characteristics such as corners and colours, but also to complex stimuli that have acquired special meaning through experience Audition Sound: pressure waves in air, water, or some other conducting medium; the resulting vibrations cause successive waves of compression and expansion among the air molecules surrounding the source of the sound Frequency: number of sound waves, or cycles, per second (measured in hertz (Hz)- 1 hertz equals one cycle per second); the frequency is related to the pitch that we perceive: the higher the frequency, the higher the pitch  Humans are capable of detecting sound frequencies from 20Hz up to 20,000Hz Amplitude: the vertical size of the sound waves, or the amount of compression and expansion of the molecules in the conducting medium; primary determinant of the sound’s perceived loudness (expressed in decibels (db)- a measure of the physical pressures that occur at the eardrum)  The absolute threshold for hearing is arbitrarily designated as 1 decibels, and each increase of 10 decibels represents a tenfold increase in loudness  At a speed of approximately 1,200 km/h, sound waves travel into n auditory canal leading to the eardrum, a movable membrane that vibrates in response to the sound waves  Beyond the eardrum is the middle ear, a cavity housing three tiny bones- the vibrating activity of these bones- the hammer (malleus), anvil (incus), and stirrup (stapes)- amplifies the sounds waves more than 30 times  The hammer is attached firmly to the eardrum, and the stirrup is attached to another membrane, the oval window, which forms the boundary between the middle ear and the inner ear Cochlea: inside the inner ear- a coiled, snail-shaped tube about 3.5cm in length that is filled with fluid and contains the basilar membrane, a sheet of tissue that runs its length  Resting on the basilar membrane is the organ of Corti, which contains about 16,000 tiny hair cells that are the actual sound receptors; the hair cells are attached to the tectorial membrane that overhangs the basilar membrane along the entire length of the cochlea  In the case of loudness, high-amplitude sound waves cause the hair cells to bend more and release more neurotransmitter substance at the point where they synapse with auditory nerve cells, resulting in a higher rate of firing within the auditory nerve.  As well certain receptor neurons have higher thresholds than others, so that they will fire only when considerable bending of the hair cells occurs in response to an intense sound  Two competing theories were advanced to account for pitch perception : o Frequency Theory: nerve impulses sent to the brain match the frequency of the sound wave. Thus, a 30Hz sound wave from a piano should send 30 volleys of nerve impulses per second to the brain; restriction: because neurons are limited in their rate of firing, individual impulses or volleys of impulses fired by groups of neurons c
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