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York University
PSYC 1010
Rebecca Jubis

PSYC 1010 REBECCA JUBIS SENSATION & PERCEPTION MODULE 17 SENSATION: the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment PERCEPTION: the process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events BOTTOM –UP PROCESSING: analysis that begins with the sensory receptors and works up to the brain’s integration of sensory information TOP-DOWN PROCESSING: information processing guided by higher-level mental processes, as when we construct perceptions, draw on our experience and expectations - All our senses  Receive sensory stimulation, often using specialized receptor cells  Transform that stimulation into neural impulses  Deliver the neural information to our brain TRANSDUCTION: conversion of one form of energy into another. In sensation, the transforming of stimulus energies, such as sights, sounds, and smells into neural impulses our brain can interpret PSYCHOPHYSICS: the study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them ABSOLUTE THRESHOLD: the minimum stimulation needed to detect a particular stimulus 50% of the time SIGNAL DETECTION THEORY: a theory prediction how and when we detect the presence of a faint stimulus (signal) amid the background stimulation (noise), Assumes there is no single absolute threshold and that detection depends partly on a person’s experience, expectations, motivation and alertness SUBLIMINAL: below one’s absolute threshold for conscious awareness PRIMING: the activation, often unconsciously, of certain associations, thus predisposing one’s perception, memory or response  In a typical experiment, the image or word is quickly flashed, then replaced by a masking stimulus that interrupts the brain’s processing before conscious perception - Much of our information processing occurs automatically, out of sight, off the radar screen of our conscious mind DIFFERENCE THRESHOLD: the minimum difference between two stimuli required for detection 50% of the time. We experience the difference threshold as a just noticeable difference (jnd) WEBER’S LAW: the principle that, to be perceived as different, two stimuli must differ by a given percentage (rather than a given amount) SENSORY ADAPTION: diminished sensitivity as a consequence of constant stimulation  When we are constantly exposed to a stimulus that does not change, we become less aware of it because our nerve cells fire less frequently o Why, then, if we stare at an objection without flinching, does it NOT vanish from sight? – Unnoticed by us, our eyes are always moving; the continual flitting from one spot to another ensures that stimulation on the eyes’ receptors continually changes o BENEFIT: freedom to focus on informative changes in our environment without being distracted by background chatter o We perceive the world not exactly as it is, but as it is useful for us to perceive it PERCEPTUAL SET: a mental predisposition to perceive one thing and not another - Through experience we form concepts, or schemas, that organize and interpret unfamiliar information - A given stimulus may trigger radically different perceptions, partly because of our differing perceptual set, but also because of the immediate context - Perceptions are influenced, top-down, not only by our expectations and by the context but also by our emotions and motivations - Perceptual bias energizes our going for it; our motives also direct our perception of ambiguous images  Emotions also colour our social perceptions MODULE 18 VISION a) The Stimulus Input: Light Energy WAVELENGTH: the distance from the peak of one light or sound wave to the peak or the next. Electromagnetic wavelengths vary from the short blips of cosmic rays to the long pulses of radio transmission HUE: the dimension of colour that is determined by the wavelength of light; what we know as the colour names blue, green etc. INTENSITY: the amount of energy in a light or sound wave, which we perceive as brightness or loudness, as determined by the wave’s amplitude b) The Eye - Light enters the eye through the cornea, which protects the eye and bends light to provide focus PUPIL: the adjustable opening in the center of the eye through which light enters IRIS: a ring of muscle tissue that forms the coloured portion of the eye around the pupil and controls the size of the pupil opening LENS: the transparent structure behind the pupil that changes shape to help focus images on the retina RETINA: the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information ACCOMMODATION: the process by which the eye’s lens changes shape to focus near or far objects on the retina - The retina doesn’t ‘see’ the a whole image, rather its millions of receptor cells convert particles of light energy into neural impulses and forward those to the brain  There, the impulses are reassembled into a perceived, upright seeming image i. The Retina RODS: retinal receptors that detect black, white, and gray; necessary for peripheral and twilight vision, when cones don’t respond CONES: retinal receptor cells that are concentrated near the center of the retina and that function in daylight or in well-lit conditions. The cones detect fine detail and give rise to color sensations  The light energy trigger chemical changes that would spark neural signals, activating nearby bipolar cells o Bipolar cells in turn would activate the neighboring ganglion cells --> optic nerve OPTIC NERVE: the nerve that carries neural impulses from the eye to the brain BLIND SPOT: the point at which the optic nerve leaves the eye, creating a ‘blind’ spot because no receptor cells are located there FORVEA: the central focal point in the retina, around which the eye’s cones cluster  Each one transmits to a single bipolar cell that helps relay the cone’s individual message to the visual cortex o Rods share bipolar cells with other rods, sending combined messages c) Visual Information Processing - Information processing begins in the retina’s neural layers which are actually brain tissue that migrate to the eye during fetal development; help encode and analyze sensory information  The same sensitivity that enables retinal cells to fire messages can lead them to misfire ii. Feature Detection FEATURE DETECTION: nerve cells in the brain that respond to specific features of the stimulus, such as shape, angle, or movement  These cells pass tis information to other cortical areas, where teams of cells (supercell clusters) respond to more complex patterns o For biologically important object and events, we have a ‘vast visual encyclopedia’ distributed as specialized cells o These cells respond to one type of stimulus o Other cells integrate this information and fire only when the cues collectively indicate the direction of someone’s attention and approach iii. Parallel Processing PARALLEL PROCESSING: the processing of many aspects of a problem simultaneously; the brain’s natural mode of information processing for many functions, including vision. Contrasts with the step-by-step (serial) processing of most computers and of conscious problem solving  Separate visual systems for perception and action illustrate dual processing- the two- track mind d) Color Vision - Color like all aspects of vision, resides not in the object but in the theatre of our brains, as evidenced by our dreaming in color YOUNG- HELMHOLTZ TRICHROMATIC (THREE-COLOR) THEORY: the theory that the retina contains three different color receptors- one most sensitive to red, one to green, one to blue- which, when stimulated in combination, can produce the perception of any color  Most people with color-deficient vision are not actually ‘colorblind’ o They simply lack functioning red-or green-sensitive cones, or sometimes both o Their vision is monochromatic (one-color) or dichromatic (two-color) instead of trichromatic, making it impossible to distinguish the red and green - Hering, found a clue in afterimages, where trichromatic theory lacked evidence of leaving some parts of the colour vision  Colour processing occurs in two stages 1) The retina’s red, green, and blue cones respond in varying degrees to different color stimuli (Young- Helmholtz trichromatic theory) 2) Their signals are then processed by the nervous system’s opponent-process cells (Hering’s theory) OPPONENT- PROCESS THEORY: the theory that opposing retinal processes (red- green, yellow-blue, white-black) enable color vision. For example, some cells are stimulated by green and inhibited by red; others are stimulated by red and inhibited by green VISUAL ORGANIZATION GESTALT: an organized whole. Gestalt psychologists emphasized our tendency to integrate pieces of information into meaningful wholes  In perception, the whole may exceed the sum of its parts o Our brain does more than register information about the world; we filter incoming information and construct perceptions a) Form Perception i. Figure & Ground o In our eye-brain system, our first perceptual task is to perceive any object (figure) as distinct from its surroundings (ground) FIGURE-GROUND: the organization of the visual field into objects (figures) that stand out from their surroundings (ground) ii. Grouping o We must also organize the figure into a meaningful form GROUPING: the perceptual tendency to organize stimuli into coherent groups  Proximity; we group nearby figures together. We see not six separate lines, but three sets of two lines  Continuity; we perceive smooth, continuous patterns rather than discontinuous ones. This pattern could be a series of alternatives semicircles, but we perceive It as two continuous lines- one way, one straight  Closure; we fill in gaps to create a complete, whole object. Thus, we assume that the circles on the left are complete but partially blocked by the (illusory) triangle. Add nothing more than little line segments to close off the circles and your brain stops constructing triangles b) Depth Perception DEPTH PERCEPTION: the ability to see objects in three dimensions although the images that strike the retina are two-dimensional; allows us to judge distance VISUAL CLIFF: a laboratory device for testing depth perception in infants and young animals  Biological maturation predisposes us to be wary of heights and experience amplifies that fear i. Binocular Cues BINOCULAR CUES: depth cues, such as retinal disparity, that depend on the use of two eyes  The greater the retinal disparity, or difference between the two images, the closer the object RETINAL DISPARITY: a binocular cue for perceiving depth: By comparing images from the retinas in the two eyes, the brain computes distance- the greater the disparity (difference) between two images, the closer the object ii. Monocular Cues MONOCULAR CUES: depth cues, such as interposition and linear perspective, available to either eye alone  Relative Height; we perceive objects higher in our field of vision as farther away  Relative Motion; As we move, objects that are actually stable may appear to move  Relative Size; if we assume two objects are similar in size, most people perceive the one that casts the smaller retinal image as farther away  Linear Perspective; Parallel lines appear to meet in the distance. The sharper the angle of convergence, the greater the perceived distance  Interposition; If one object partially blocks our view of another, we perceive it as closer  Light & Shado
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