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Chapter Notes 5.docx

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Western University
Psychology 1000
Terry Biggs

Psychology Chapter 5- Notes Chapter 5 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 peoples 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 Webers 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 Webers 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 pupils 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
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