Psyc 304 1.pdf

Visual Development PSYC 304 Sonia Krol, PhD September 9th, 2024 Outline Methods in infant research Visual acuity and colour perception Face perception Object perception What do babies see at birth? ⓘ Start presenting to display the poll results on this slide. What do ba...

Visual Development PSYC 304 Sonia Krol, PhD September 9th, 2024 Outline Methods in infant research Visual acuity and colour perception Face perception Object perception What do babies see at birth? ⓘ Start presenting to display the poll results on this slide. What do babies see? Until a few decades ago, it was assumed that infants’ vision was almost non-existent and barely functional This is wrong From birth, babies visually scan environment and pause to look at stuff So what exactly can they see? Can’t ask babies so have to get creative Methods in Infant Research Methods in Infant Research Preferential looking paradigm Habituation paradigm Preferential Looking Paradigm Assesses infants’ preference for one stimulus over another Present the baby with 2 stimuli beside each other at the same time If the baby looks longer at one stimulus than the other, it means that: 1. they can distinguish between the two 2. have a preference for one over the other Fanz, 1961 Preferential Looking Paradigm What is interesting to infants? Infants prefer to look at stimuli that are: More complex, more saturated in colour Familiar Habituation Paradigm Paradigm takes advantage of babies’ natural preference for novelty Assesses infants’ ability to discriminate between stimuli Habituation phase: repeatedly present infant with a stimulus until they habituate to it Reduced or stopped response to a stimulus e.g., looks at it less Wait for infant to get bored Habituation Paradigm Paradigm takes advantage of babies’ natural preference for novelty Assesses infants’ ability to discriminate between stimuli Habituation phase: repeatedly present infant with a stimulus until they habituate to it Test: Present habituated, “old” stimulus with a new stimulus: Dishabituation: If the baby shows greater interest in/looks longer at the new stimulus, they can tell the difference between the two If the baby looks at stimuli equally, they can’t tell the difference between stimuli  Habituation Paradigm Habituation phase: Test: Familiarity vs. Novelty In general, infants show a preference for familiar stimuli Prolonged/ repeated exposure to a stimulus will cause infants to shift their preference to a novel stimulus Summary Preferential-looking paradigm: 2 stimuli presented side-by-side Assesses an infants’ preference for one stimulus over another Prefer familiar and/or complex stimuli Habituation paradigm: Infant presented with a stimulus many times until they get bored of it (habituation) and on the test trial, presented with this old stimulus beside a new, different stimulus Assesses an infants’ ability to distinguish between 2 stimuli Prefer novel stimuli as indicated by greater looking time (dishabituation) Visual Acuity and Colour Perception Visual Acuity Sharpness of visual discrimination Assessed by using preferential looking paradigm Infants presented with a succession of paddles with increasingly narrower stripes and narrower gaps between them until infant can no longer distinguish between stripped paddle and plain gray one Visual Acuity At birth, infants have poor visual acuity prefer to look at patterns with high visual contrast don’t discriminate between stimuli with lower contrast sensitivities Visual Acuity At birth, infants have poor visual acuity prefer to look at patterns with high visual contrast don’t discriminate between stimuli with lower contrast sensitivities Why? Due to immaturity of cone cells in infants’ retinas Cone cells: light sensitive neurons involved in seeing fine details and colours 8 months: adult-like visual acuity Development of Visual Acuity  Colour Perception At birth: infants see in gray scale 2 months: colour vision appears 5 months: adult-like colour perception Due to maturity of cones and visual cortex Can discriminate between colour categories and between hues of the same colour Habituation phase: Habituation phase: Test: Test: Visual Acuity and Colour Development Visual Scanning From birth: infants scan their visual environment and pause to look at something BUT trouble tracking moving stimuli because eye movements are jerky 4 months: able to smoothly track moving objects if moving slowly 8 months: adult-like visual scanning; can smoothly follow objects Improved visual scanning due to brain maturation The ability to visually scan is important because one of the few ways that infants have control over what they observe and learn Rosander, 2007 Face Perception Face Perception Newborns show a preference for faces or face-like stimuli vs. non-face like stimuli Why are infants drawn to faces? Special innate face perception mechanism? Why are infants drawn to faces? Special innate face perception mechanism or more general mechanism? Hypothesis: Infants have a general bias for stimuli that are more “top heavy” vs. “bottom-heavy” Preferential looking paradigm Showed babies: regular faces upside-down faces scrambled, top-heavy faces scrambled, bottom heavy faces Macchi et al., 2004 Why are infants drawn to faces? If faces are special, babies should always prefer to look at upright face If general bias for top-heavy stimuli, babies should prefer upright face AND scrambled top-heavy faces Macchi et al., 2004 Why are infants drawn to faces? Preference for upright face over upside-down face Macchi et al., 2004 Why are infants drawn to faces? Preference for top heavy scrambled face vs. bottom heavy scrambled face Macchi et al., 2004 Why are infants drawn to faces? Suggests that preference for faces simply result of general preference for stimuli that are “top-heavy” rather than “bottom-heavy” Macchi et al., 2004 Seeing Mom’s Face Infants very quickly learn to recognize and prefer their own mother’s face Just a few days after birth, babies prefer their mother’s face compared to another woman’s face Becoming a Face Specialist Over 1st year of life, infants’ become face specialists Better at distinguishing between faces that are frequently experienced in their environment Worse at distinguishing between faces that they encounter less frequently Other-Race-Effect in Infants Other-race-effect: People find it easier to distinguish between faces of individuals from their own racial group than between faces from other racial groups Also evident in infants: Researchers recruited Caucasian, Black, and Chinese infants Habituated infants to: Face from their own race OR Face from another race Then presented habituated face with a new face from the same race Can infants distinguish between the two faces? Kelly et al., 2009  Other-Race-Effect in Infants Habituation: Habituation: Test: Test: Kelly et al., 2009 Other-Race-Effect in Infants Results: 3 month olds: easily distinguish between faces of all races 9 month olds: better at distinguishing between faces of own race Not innate, but rather exposure effect During the first few months of life, 96% of faces that babies are exposed to are females from their own race (Sugden et al., 2014) If infant is equally exposed to faces of different races, will not show other- rate-effect Kelly et al., 2009 Perceptual Narrowing Tuning of perceptual mechanisms to the specific sensory inputs that infants encounter in their daily life Improves perception of stimuli encountered often Decline in the ability to distinguish stimuli that are not present in the infant’s environment Present for several perceptual domains Result of synaptic pruning Recap: Synaptic Pruning Synaptic pruning: Elimination of synapses to increase the efficiency of neural communication Follows “use it or lose it” principle Synaptogenesis: Formation of synapses between neurons Rapid synaptogenesis right after birth Results in hyper-connectivity in the brain Recap: Synaptic Pruning Synaptic Pruning across Domains Face Perception in Children with ASD People with autism spectrum disorders (ASD) often have difficulty with face perception, e.g., prefer to not look at eyes Toddlers with ASD preferred looking at geometric shapes over pictures of people Opposite for typically developing kids Infants’ preference for non-faces could be an early indicator that the infant will later be diagnosed with ASD Pierce et al., 2016 Summary of Face Perception From birth, infants have a preference for faces, especially their mother’s face Face preference is not innate but rather a result of general preference for top-heavy stimuli 9 months: Infants become face specialists as a result of perceptual narrowing Other-race effect in infants Object Perception Perceptual Constancy The perception of objects as being constant in size, shape, colour. etc in spite of physical differences in the retinal image of the object Perceptual Constancy in Infants Study: Is perceptual constancy present from birth? Habituation paradigm with newborns: Habituation: Repeatedly show infant a small cube Cube shown at different distances on each trial i.e., retinal image changed from trial to trial Do infants perceive these as the same object or as different objects? Test: Show infant the original, small cube and an identical larger cube Larger cube farther away so that both cubes projected the same-size retinal image Slater et al., 1990 Perceptual Constancy in Infants Slater et al., 1990 Perceptual Constancy in Infants Results: Infants looked longer at the larger but further away cube Indicates that they see it as different in size from the original, smaller cube Means that infants saw the repeated presentations of the original, small cube as a single object of a constant size, even though the retinal image varied Suggests that perceptual constancy is present from birth Slater et al., 1990 Object Segregation The ability to identify that objects are separate from each other Movement is an important cue Separate objects move independently of each other Object Segregation in Infants Habituation paradigm with newborns and 4 month olds Habituation: Repeatedly watched video of a rod moving side-to-side behind a box Do infants see the rod as a single rod or as 2 separate short rods? Test: Shown 2 rod stimuli moving side-to-side One rod vs. a broken rod Kellman & Spelke, 1983 Object Segregation in Infants Results: 4 month olds: Preferred to look at the broken rod Indicates that they understood that the rod behind the box is one object Newborns: Looked the same amount of time at broken rod and single rod Indicates that did not understand that rod behind the box was a single object Suggests that object segregation is not innate, has to be learned with experience Also relies on improvements in visual scanning Kellman & Spelke, 1983 Depth Perception Binocular disparity: Difference between the retinal image of an object in each eye that results in two slightly different signals being sent to the brain Visual cortex combines the differing neural signals caused by binocular disparity Depth perception relying on binocular disparity is present at 4 months old Sensitive Period for Binocular Vision Sensitive period: a biological period during which certain kinds of experiences are necessary for an ability to develop normally Sensitive period for binocular vision: From birth to age 3 Depth perception from cue of binocular disparity is a natural result of brain maturation as long as the infant receives normal visual input from both eyes If infants do not receive normal binocular visual input until age 3, they may fail to develop normal binocular vision and have life-long difficulties with depth perception Depth Perception Monocular depth cues: depth cues perceived with one eye e.g., relative size or overlap Perceived at 6 months old Assessed using visual cliff Visual Cliff Depth Perception Monocular depth cues: depth cues perceived with one eye e.g., relative size or overlap Perceived at 6 months old Assessed using visual cliff 6 month olds will not crawl over visual cliff but younger children will Suggests that this aspect of depth perception needs to be developed through experience Also relies on improvements in visual acuity Visual Development Timeline At birth: rudimentary visual scanning, poor acuity, preference for high contrast, gray scale, preference for faces vs. non-faces, perceptual constancy 2 months: colour vision appears 4 months: object segregation and binocular depth perception appear 5 months: adult-like colour perception 6 months: face generalists, monocular depth perception appears 8 months: adult-like visual scanning and visual acuity 9 months: face specialists through perceptual narrowing Some visual abilities are native but refined and specialized with experience The Nature and Nurture of Visual Development Innate: Perceptual constancy and preference for top-heavy stimuli Improve with brain maturation: visual acuity, colour perception, and visual scanning Experience dependent processes: Object segregation Face perception (perceptual narrowing) Depth perception (sensitive period of binocular vision)