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PSYC 2220 (44)


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York University
PSYC 2220
Richard Murray

Chapter 16: Perceptual Development Basic Visual Capacities - present day research: "infants have some perceptual abilities" - 19th century psychologists: "infants perceptual world = nonexsitant" this is b.c psychs learned how to measure infants perceptual abilities  its very challenging to run perceptual tests on newborns Methods used in newborns to determine Visual Acuity Preferential Looking Technique (PL) IE: if infant is presented with greyfield or high contrast contours, he'll look at the contours  observer doesnt know which stimulus is being presented = avoids bias  if infant looks @ one stimulus more than other = he can tell the diff. b.w them  works due to spontaneous looking preferences: infants prefer to look @ certain type of stumli  measure acuity by determining the narrowest stripe that results in looking more to one side  grating + grayfield have same avg. light intensity Visual Evoked Potential (EVP)  recorded by disk electrodes placed on back of head over V1  infant looks @ grey field that is replaced quickly either by grating or checker pattern  EVP is evoked if stripes/checks = large enough to be detected by V1 by generating an electrical repsonse  if stripes = too thin = no response  newborns cones = less visual pigment = dont absorb light as effectively as adult cones  fat inner segment = course receptor lattice = large space b.w outer segments ≠ well suited for detecting fine detail  cone receptor outer segments cover 68% of adult fovea but 2% of newborn = most of light enertering neewborn fovea is ost in spaces b.w the cones + not useful in vision visual acuity: measure of ability to see fine detail  to determine how infant perceives env we need to determine contrast sensitivity Contrast Sensitivity  gratings used to measure CSF are low contrast Perceiving Colour  newborns ≠ good colour vision  colour vision develops early (present w.in 3-4 months) light stimulus varies on 2 dimensions (1) chromatic colour (2) brightness  issue: ppl can tell the difference b.w colours even if they cant see them due to brightness (ie: yellow brighter than red, even at greyscale)  when stimuli w. diff wavelengths are used to test colour vision, their intensity should be adjusted so theyre the same brightness Perceiving Depth  diff types of depth info become operative @ diff times  first binocular, later pictorial + depth cues  binocular fixation: the 2 eyes are both directly looking at the object = two foveas directed to exactly same place [requirement of binocular disparity]  by 2-3yrs: fairly good binocular disparity, dont reach stereoacuity adult levels until about 12 can use binocular disparity as a cue by 4 months  disparity from binocular fixation doesnt guarantee that infant can use this info to perceive depth  pictorial cues also provide de
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