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Chapter 5

Chapter 5 Perceptual Development PSY312

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University of Toronto Mississauga
Hywel Morgan

Chapter 5: Perceptual Development -Even in the first half year, infants connect sights and sounds in meaningful ways ex: 4 month old girl is shown two videos one of a lady playing peek-a-boo and one of a hand striking a block. The experimenter would play the soundtrack of one. The infant looked at the right video screen -greater perceptual abilities in young infants than might have been expected 1. Perceptual functioning reaches adult like or near adult like levels remarkably rapidly. Even newborns can see, hear, integrate info from diff sensory systems and these abilities continue to develop rapidly during first year 2. Perception and action are closely connected, and this connection is present from infancy. Perception provides children with info that they use to guide actions, and actions generate perceptual info for the developing child PERCEPTION AND HUMAN NATURE -How do biological and experimental factors interact? -Locke and Berkeley suggest that perceptual abilities are learned. -infants might at first experience the world in terms of isolated lines and angles, then they learn they are objects, then infer properties of the objects -William James hypothesize that infants experienced the world as a "great blooming, buzzing confusion" -Gibson argued that perceptual abilities that are essential to survival are built into the infant; perception and action closely related -perceptual learning is a process of learning to detect info that is available in the environment -both biological and experimental factors -all current theories recognize that people are biologically prepared to perceive the world in certain ways and that many important perceptual capabilities are present at birth -recognize that experience contributes to the development of perceptual abilities -perception and action are closely connected from the beginning of life (ex when infants see a rolling ball they move their hands to where the object will be by the time their hands arrive) -linkage between perception and action is evident at neurophysiological level as well as behavioural level -Vision System: ventral system: carries info in large part to temporal cortex of the brain, is specialized for recognizing and representing the visual world dorsal system: carries info largely to the parietal cortex, is specialized for using perceptual info to guide action -perception provides info needed to act effectively in the environment. -allows us to stay in touch with a constantly changing world THE TASK OF PERCEPTION -vision, audition, gustation, olfaction, touch -task of perception needs to accomplish three functions attending: involves determining what in a situation is worthy of detailed processing identifying: involves recognizing what we are perceiving locating: involves specifying how far away the perceived object or event is and in what direction relative to the observer -effectively guiding action -we rely most heavily on sight and sound Vision -light impinges on the eye, progresses through the cornea and pupil to the lens. -lens bends the light rays to project a focused image on the light sensitive retina -accommodation: change in the shape of the lens that brings the object into focus Retina -two types of photoreceptor cells -rods and cones -cones are concentrated in the fovea, small, vision is sensitive, responds to diff wavelengths of light and comparing the outputs of diff types of cones enables colour vision, used for day vision -rods are responsive in dim light, good for night vision, located in the periphery of the retina -from the retina, info is relayed to the brain by way of the optic nerve -visual cortex of the brain registers the info and integrates it with previous info to form a representation of the visual scene -eye movements, provided the key to revealing the perceptual world of infants -researchers have developed two primary methods for studying infant visual perception, and both capitalize on the fact that infants turn their heads toward what interests them 1. Preferential Looking paradigm, two objects or events that differ in only one way are displayed side by side and the researcher examines whether infants consistently look more at one of them (ex if shown red and grey ball repeatedly and looks at red consistently, then they must perceive diff in colour) 2. Habituation paradigm, based on infants propensity to look more at objects that interest them and on the fact that like older individuals, infants grow bored with objects that are presented repeatedly -familiarization phase: object presented repeatedly -when infant no longer look at it much, a new object that differs in some specific way is introduced. If they show interest again, they must perceive a diff between the two Attending to Visual Patterns -cognitive growth will presumably be more rapid if infants orient to informative parts of the environment rather than to uninformative -Cohen made an important distinction between attention getting & attention holding properties of stimuli -gross physical characteristics of objects attract initial attention, but the objects meaningfulness determines whether attention persists -same attention getting properties influence perception throughout life -attention holding change with age and experience THE ORIENTING REFLEX -sudden loud noise, flash of light -present from birth -adaptive in helping people react quickly to events that call for immediate action -controlled by cortex but mostly by subcortical brain region - 1 mo infant with no cortex: anencephalic; its ability to orient and habituate prove that cortical activity is not needed for these processes to occur -usually in 2 mo, because cortical activity may hinder orienting, so that 1 mo without cortex was advanced OVERT & COVERT DEPLOYMENT OFATTENTION -overt behaviour: attention attracted by object or event -covert behaviour: ppl look at one thing but their minds are on something else entirely -Johnson, Posner, Rothbart: exposed 4 mo to appearance of diamond in periphery, colour wheel on other side -even tho 4 mo were not looking directly at the diamond, they were attending to it, demonstrating that they were capable of covert as well as overt attention RULES FOR SCANNING THE ENVIRONMENT -Haith suggested that newborns act as if the know the following 5 rules for finding the interesting part of their environment 1. If awake , light not too bright, open eyes 2. If darkness, scan environment intensively 3. If light, scan the environment broadly 4. If you find an edge, stop scanning broadly and continue scanning around the edge 5.when you are scanning near an edge, reduce the range of fixations perpendicular to the edge if there are a lot of contours in the are -may cause them to miss others -may lead to infants excluded interiors -age related changes in scanning patterns, as well as other changes in infants attention, appear to be due in large part to the relative rate of maturation of visual cortex and the subcortical structures -subcortical structures are more mature (dominant) at birth and therefore seem to play a larger role in directing attention in the first months than do later -tend to look at outlines of objects, faces, eyes -many sources of evidence converge to suggest that there is a shift from initial subcortical dominance to later increasing cortical involvement in the deployment of visual attention STIMULUS COMPLEXITY -one attention holding property appears to be moderate stimulation -prefer moderately bright object over dim and very bright -if a loud noise is heard before the choice of objects, they pick the dim one -Maurer said its due to infants' trying to modulate the total amount of incoming stimulation -increasing sound, sight, touch small amounts, same as increasing one of them by a large amount -infants prefer to look at moderately complex objects -moderate discrepancy hypothesis: infants are most interested in looking at objects that are moderately discrepant from their existing capabilities and knowledge -as the child's ability to deal with complexity increased, they preferred more complexity -if people are programmed to orient toward material that is just beyond their current understanding, they continually will be pulled toward more sophisticated attainments EXPECTATIONS -expectations that infants form change with developments Summary: -loud noises, sudden flashes, changes in environment, attract attention of newborns -newborns can the environment in ways that lead them to attend to most important info -can attend to locations covertly -preference for moderate degree of stimulation and by experiences they form Identifying Objects and Events VISUALACUITY (vision for fine detail): single capability that is most crucial for identifying objects and events is the ability to discriminate them from the ongoing flux of visual stimulation -similarities and differences among stimuli (Snellen chart in eye doctor) -infants preferences for looking at one object rather than another can yield similar info.Almost all infants would rather look at alternating black and white stripes than at undifferentiated gray fields -spatial frequency: how much space between stripes infants need to see the difference -infants acuity: 20/6060 -differences between infants and adults pattern vision are present not just in the absolute sensitivity, but in where the greatest sensitivity is -1 mo is best at very low spatial frequencies (wide separated stripes) -infants who are born with cataracts that prevent visual input, removed within 6 months of life and fitted with contact lenses so they can receive appropriate visual input, immediately after surgery, acuity is the same as a newborns, improves rapidly even within 1st hour after surgery -visual experience appears to be crucial for the development of visual acuity MOTION -young infants attention is drawn to moving objects and their sensitivity to motion increases with age -newborns have some ability to track moving objects smoothly but has to be big and move slow -smaller or faster moving objects, eye movements are not as smooth -with age, infants become better able to smoothly track moving targets using both head and eye movements -development of smooth visual tracking coincides with the development of sustained attention to visual stimuli -fact that motion attracts our attention also is useful b/c it helps us identify objects -Gibson suggests that infants might be able to perceive the unity of different parts of a single objects if the object is moving (attracts attention and helps them identify what they are seeing) COLOUR -400-700 nm, wavelengths as colours -categorical perception: diffs between categories (such as yellow and green) seem greater than differences within a category (various shades of yellow), even when the physical diffs are identical -infants display categorical perception of colour, and they place the boundaries between colours at the same places that adults do - long before they learn the colour names -biological makeup plays a critical role in colour perception SOCIAL PERCEPTION -Infants prefer looking at faces than objects. They like the symmetry, high contrast, movment, sound; liking for individual features than perceiving faces are faces -Dannemiller and Stephens, by 3 months, faces special for infants -at 6 weeks infants look at FigureAand B as the same -at 12 week they strongly prefer figureA -no change toward preferring Figure C and D, thus demonstrating that the change toward preferring the
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