MLSC609 Week 10 of 11: Perceptual Development, Attention

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MLSC609 Week 10 of 11 Perceptual Development,
Attention
Psychology 351 Perceptual Development
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What can babies see,and when can they see it?
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William James (1842-1910)

• Babies see a blooming, buzzing confusion?
• Q On what basis did he make this claim?
• A Not much evidence around in his time no
  clever methods were available to test infants

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Are we born with our sensory gearfully
functioning?

• Some of it, yes other components, no
• In humans, the eye is only ½ its adult volume at
  birth (c.f. 1/20 for the rest of the body)
• Distance from cornea to retina grows from 16 mm
  at birth to 24 mm in adulthood
• Rods and cones are present, functioning from
  birth
• The periphery functions much like it will in
  adulthood
• The central fovea is not well defined cones are
  stubby and more sparse

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With aging, cones elongate, pack more densely,
and migrate toward the retinas center to form
the fovea
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Are we born with our sensory gearfully
functioning? (continued)

• By one year, all the receptors are behaving like
  those of adults
• Optic nerve fibers become myelinated rapidly
  during first 4 months, reaching asymptote at two
  years
• Number of cortical cells in V1 is remarkably
  constant from 28 weeks from conception to age 70
  years (cf. significant losses in other species,
  where programmed cell death is common)
• Major principle Sensory stimulation is mandatory
  for development to progress!

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Brain pathways

• Brain pathways for vision are not fully known in
  humans they are better understood in newborn
  cats at the time they first open their eyes.

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Brain Development

• From 25 days following conception until birth

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Human Brain Development Axial slices at25 40
weeks
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Human Brain Development Connection Density
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Humans are slower to mature than are most/all
other species

• Retinal ganglion cells
• Adult-like responses of center-surround RFs,
  adult proportion of on/off center
• Immature responses include a low level of
  activity, overly large receptive fields, slow
  responses to light, weak inhibition, parvo vs.
  magno responses not clearly differentiated
  (recall that parvo handles color and detail
  magno handles movement and depth)
• Lateral geniculate nucleus
• Adult-like responses include normal visual field
  mapping, binocular separation of inputs
• Immature responses include low overall activity,
  silent areas, overly large receptive fields, slow
  responses, quick fatigue

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Human Brain Development

• Superior colliculus
• Adult-like responses include normal visual field
  mapping, normal center/surround RFs and on/off
  center ratios
• Immature responses include slow responses, quick
  fatigue, large receptive fields, no movement
  direction sensitivity
• Striate cortex (V1)
• Adult-like responses include normal visual field
  mapping, adult separation by eye of input
• Immature responses include slow responses, quick
  fatigue, many silent cells, fewer or absent
  orientation- and direction-sensitive cells with
  broad tuning curves, no binocular disparity cells

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Human Brain Development

• Conclusion the quality of visual information
  reaching the highest brain centers for human
  vision is probably of low quality at birth.
• In humans, the number of synaptic connections in
  V1 grows steadily to a peak at 9 months past
  birth, then declines steadily through life (as
  specialized connections come to dominate,
  presumably)

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Methodology for studying infant vision

• Its tricky getting babies to cooperate, follow
  instructions!
• Passive measures e.g., visually evoked
  potentials (VEPs) can be recorded from infants

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Methodology for studying infant vision

• Active measures (1) preferential looking with
  blind scoring or recording eye movements (2)
  habituation/dishabituation paradigm measuring
  pupil dilation, heart rate, other measures of
  orienting or surprise.

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Methodology for studying infant vision

• Limitations of preference method
• Reliance on preferences for familiarity vs
  novelty
• The one-sided nature of logic

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Infants and Eye Movements

• Two-week old infants can look at a target and
  place it in their fovea with high accuracy
• Saccadic eye movements slower to initiate in
  infants they tend to make a series of small
  saccades rather than fewer long ones
• Smooth pursuit eye movements are not seen in
  young infants rather, they track through many
  small saccades. Adult-like smooth pursuit with
  anticipation comes in at 8 10 weeks.
• Optokinetic nystagmus (reflexive eye tracking of
  large moving textured fields) infants show an
  approximation to it as early as 5 days (albeit
  less smooth in younger infants than in older).
  OKN can be used to test an infants acuity by
  making stripes narrower or the texture finer

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Infants and Eye Movements

• Infants will fixate a stimulus that moves in the
  visual periphery but show greater sensitivity to
  movement in the periphery up until 2 months (with
  a smaller asymmetry persisting into adulthood)
• Infants visual acuity is poor, especially in the
  periphery approximately 20/800 at birth, not
  good enough to read the E at the top of a Snellen
  chart (improves to 20/20 at 1 year).

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Infants and Visual Acuity

• Infants visual acuity is poor, especially in the
  periphery approximately 20/800 at birth, not
  good enough to read the E at the top of a Snellen
  chart (improves to 20/20 at 1 year).

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Infant Visual Acuity
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Contrast Sensitivity Functions
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Simulations of Visual Acuity
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More on acuity

• Newborns act as though their lens were
  inflexible, fixed at 20 cm focus.
  http//www.opt.indiana.edu/people/faculty/candy/Vi
  sualDevelop/Infant_Vision_Lab.htm
• Acuity improves rapidly over the first three
  months.
• Contrast sensitivity infants appear to see only
  big blobs www.owlnet.rice.edu/psyc351/Images/Modu
  lationTransferFunction.bmp
• http//www.eyes.arizona.edu/Research/VisualDevelop
  ment/IVLab/tellers.html
• With age, infants will focus on edges, corners,
  etc., not on empty space.

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• Brightness one-month old infants are only 1/50
  as sensitive to light as are adults three-month
  olds rise to 1/10.
• Color perception infants are trichromats
  (determined by preferential looking,
  dishabituation)
• Short-wavelength sensitive cones are immature,
  however
• Binocular fixation develops 3 months (a
  prerequisite to stereopsis)
• Random dot stereograms quintessential method,
  but again, its 1-sided
• For more http//www.ski.org/Vision/babyvision.htm
  l?id10

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Visual Cliff Eleanor Gibson (National Medal of
Science, 1992)
Will baby come to momma?
6-month olds decline to crawl to their mothers
over the cliff 2-month olds (not crawling yet)
show heart rate effects
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Movement critical for infants

• Infants show a preference for movement
• Movement key for object segregation, depth
  (parallax)
• Biological motion Infants see Johansson effect
  but miss occlusion

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Infants and Pattern Perception

• Pattern discrimination infants seem to prefer a
  moderate level of complexity
• Prefer a pattern over blank
• Prefer high contrast over low
• Prefer large over small
• Prefer many over fewer
• Prefer curved over straight

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Infants and Pattern Perception

• Faces preference for normal over scrambled
  cartoon faces at 2 months
• Is Moms face special? At 2 days, infants
  recognize her, but scarves destroy this effect

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Infants and Perceptual Organization

• Figure ground dishabituation when switching to
  ground
• http//socrates.berkeley.edu/plab/projects.htm
• Grouping rows and columns gt bars habituation
  persists
• Common fate works at 4 months according to
  Kellman and Spelke, broken or unitary rod moved
  behind block
• Movement key to object segmentation (Xu and
  Carey)

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More on Eleanor (Jackie) Gibson

• Her contribution was not just the visual cliff!
• She studied the development of expertise
• Main idea infants/experts must learn what to
  attend to in the image selective attention.
• Improvement at differentiation by attending to
  subtle cues as in wines, faces
• E.g. discriminating O vs. Q

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Milestonesin Perceptual Development

• Newborns
• Recognize mothers face
• Discriminate sound of mothers voice
• Differentiate smell and test stimuli
• Intermodal matching

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2 weeks

• Look at moving stimuli

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1 month

• Visual acuity of 20/600, vision slightly worse
  than adult night vision
• Able to see large objects with high contrast
• Categorical perception of speech stimuli

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2 months

• Use motion information to see rod continuing
  behind occluder
• Short wavelength cone now present
• Minimum audible angle 27 deg (cf adult 1 deg)

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3 months

• Grouping by lightness similarity
• Perception of facial expressions
• All three cone types now present
• Binocular fixation
• Following moving stimulus with smooth eye
  movements

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4 months

• Categorize wavelengths, colors as adults do
• Discriminate between different categories of
  objects
• Perceive biological movement
• Spontaneous reaching for nearer object
• Binocular disparity becomes available as depth cue

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5 months

• Pictorial depth cues are used

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6 months

• Visual acuity is close to an adults (fully
  parity after one year)
• Hearing thresholds are within 10-15 db of adult
  level
• Equivalence classification for speech

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8 months

• Sensitive to occlusion in biological motion

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Critical Periods

• Definition ranges of time during which infants
  must receive appropriate stimulation or risk
  losing the ability to perceive certain stimuli.
• Human children remain susceptible to the adverse
  effects of visual deprivation until about 7 to 8
  years of age.

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Critical Periods

• Infantile cataracts prevent the perception of
  well-defined spatial stimuli essential for
  developing the cortical "feature detectors"
  needed for good spatial vision.
• If left untreated for the initial 6 months,
  infants can be impaired for life.
• Critical period for binocular function begins at
  6 months and peaks from 1 to 2 years