Learning and Development
• The nature/nurture debate
• Sources of evidence
– adult perception
• set
• learning
• adaptation
– cultural differences
– infant abilities
– animal deprivation studies
• human equivalents
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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The Nature/Nurture Debate
• Which aspects of perception are innate and which are
learned?
– cannot be all innate - need flexibility based on learning new perceptions
– cannot be all learned - if you have to learn everything, how would you
begin?
• How modifiable is perception?
– What is “learned” in perceptual learning?
• What is the degree of neural plasticity?
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Adult Perception
• Set - expectations
–
–
–
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ambiguous figures (e.g. old/young woman)
Street figures - verbal labels influence organization
Scene perception - seeing what you expect to see
context to set the expectations
• music, stories, previous pictures, other information
• Learning new discriminations
– alphabet letters
– wine, food, trees, newly hatched chicks, Braille
– blindsight - echolocation
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Adult Perception
• Adaptation
– Kolers and Stratton - prism adaptation studies
• inverting prisms put retinal image upright but make world look upside
down
• after extended wear the world begins to look normal (right side up)
• but ONLY if
– not see part of your own body
– you move around (no passive adaptation)
• in their studies participants rode bicycles, flew airplanes
• after extended wear, when you take the lenses off with your normal
vision the world looks upside down
– must readapt to the normal view
• what is changing in this type of adaptation?
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Culture
• Cultures studied include:
– western, urban culture
• “carpented environment” - many straight lines and right angles
– eskimos
• igloos, primarily white environment, long vistas
– desert nomads
• tents (irregular with lots of curves), beige, long vistas
– African plains (savannas)
• rounded huts, long vistas
– deep jungle (rain forest) tribes
• rounded huts, green, short views (no horizon line)
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Culture
• Color perception
– some cultures use very few color words (1 - 4)
• do they not see the other colors?
– Eskimos have hundreds of words for white (mostly variations on conditions
of snow)
• do they see more shades of white than westerners?
– All the differences have been found to be differences in “naming” not
perception. We all seem to be able to discriminate the same number of
colors, different cultures choose to name more or less of them.
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Culture
• Geometric Illusions
- The Muller-Lyer Illusion is only
seen by people raised in a
“carpented” environment (Western
cultures). People raised without
seeing carefully squared off
buildings are not subject to the
illusion.
- Which cultures would not see this
illusion?
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Culture
• Geometric Illusions
- The Vertical-Horizontal Illusion is seen
primarily by people who are raised with
experience seeing long vistas. The
“horizon line” is perceived as shorted than
the vertical line. People without experience
seeing the natural horizon are less
susceptible to this illusion.
- Which cultures would not see this
illusion?
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Culture
• Pictorial Depth
– people with out prior exposure to the use of the pictorial depth cues cannot
use them to interpret photographs or pictures.
• Historical use of depth cues in representation
– Byzantines and Greeks knew about the pictorial depth cues and used
perspective in their art.
– The Egyptians did not use pictorial depth cues and their art sometimes looks
odd to us.
– Some recent and current tribal cultures also do not use perspective.
• Pictorial depth cues are learned
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Culture
• Split-half drawings
This is a split-half representation
of a bear rendered by Pacific
coast indians.
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Culture
Split-half drawings
When asked what
an elephant looked like from
above, both children and
adults in Africa chose the
image on the left.
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Culture
Examples of images used
to test pictorial depth
perception in African
tribes.
The upper picture is the test.
Subjects are asked which animal the
man is about to spear.
The lower picture shows the true size
relationships.
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Culture
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Infant Abilities
• At birth the sensory systems are not fully developed.
• Research techniques
– preferential looking
– VER (VEP) - scalp electrodes are used to record electrical responses of the
brain in response to stimuli
– habituation
• sucking rate
• movement
– visual cliff
– heart rate
– emotional response
– conditioned head turn
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Visual Cliff
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Infant Abilities
• Vision
– acuity - can see about 9 inches away
• adult acuity is about 1 minute of visual angle, the one month old is 40
minutes, the six month old is 6-7 minuts
– color - similar to adults
• neonates do not see blue as well but by 2 months normal color vision
– pattern preferences
• patterns over plain (even in premature infants)
• high contrast
• larger patterns
• many rather than few
• curves over straight lines
• moderate complexity
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Infant Pattern Preferences
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Infant Pattern Preferences
Faces are strongly preferred and
this preference increases with
age. The white bars represent
neonates less than five days old.
The striped bars represent 2-6
month old infants.
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Infant Pattern Preferences
Infants as young as four days old
prefer the patterns with facial
features, but it is not until they are
two months old that they reliable
prefer the pattern with the
features in the correct locations.
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Infant Abilities
• Vision
– depth
• infants prefer three dimensional images
• infants will not cross the visual cliff by 6 - 14 months
• the use of virtual images indicates that infants have stereopsis, but they
do not have control over convergence until they are two years old
• by two months old they respond to the optical expansion pattern
• size and shape constancy are active by 6 weeks
• monocular depth cues are learned later
– sensitivity to texture gradient increases from 6 - 16 years.
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Infant Abilities
• Audition
– Compared to adults, infants are more sensitive to high frequencies and less
to low
– By 3 minutes old infants can localize sounds
– Babies can hear inside the womb. Babies have shown recognition and
preference for stories that their mothers read to them while their mothers
were pregnant
• Touch
– Probably one of the earliest sensory experiences
– Rooting response
– Pain sensitivity equal to adults
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Infant Abilities
• Taste
– Infants are very sensitive to sweet
– Less sensitive to sour and bitter
– Sensitivity to salt does not appear until four months
• Smell
– Identification of mother’s milk
– More sensitive than adults to body odors
– From birth , turn towards pleasant odors and away from noxious odors
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Animal Deprivation Studies
• Goal
– get animal old enough to do a behavioral task without giving them any
perceptual experiences (no opportunities for perceptual learning)
• Physiology
– single cell recordings in 8 - 16 day old kittens
• generally similar set of feature detectors
• cells respond more slowly
• less selective (for example - respond to a wider range of orientations)
• Binocular deprivation
– birth to 16 months
– degeneration of optic nerve - completely blind
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Animal Deprivation Studies
• Monocular deprivation
–
–
–
–
birth to four months
blind in occluded eye, but normal vision in other eye
loss of binocular cells in cortex (disparity detectors)
no stereopsis
• Selective rearing
– raise kittens in an environment with either only vertical or only horizontal
lines
– “vertically” reared kittens cannot see walls in the horizontal maze and viceversa
– single cell recordings show loss of oriented line detectors for whichever lines
they did not experience
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Animal Deprivation Studies
• Critical periods
– kittens
• deprivation for as little as 3 days during the fourth or fifth week can
cause permanent change
• past the eighth week deprivation causes smaller changes
• after four months there is no effect of deprivatio
– a critical period is a period of susceptibility
• a single day of deprivation during the critical period can cause changes
• Organisms are pre-wired but need stimulation for
normal development and maturation
– without stimulation lose even the pre-wired mechanisms
– some amount of plasticity and re-wiring can take place
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Animal Deprivation Studies
• Critical Periods
– for very young organisms there can be re-wiring (plasticity)
• children born with 1/2 brain or very early brain damage other brain areas
can take over the functions of the missing parts
• animal studies with relocating brain parts or rearranging eye position
– although many examples are in vision there are critical periods in audition
also
• e.g. all people are born with the ability to hear all possible phonemes
from all languages. We lose those that we are not exposed to early on.
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Human Equivalents
• Binocular deprivation
– born blind - lose optic nerve
– cataracts at birth - no form perception but can see light and shadows and
sometimes color
• when cataracts are surgically removed in adulthood the person cannot
make sense of the visual information
• Monocular deprivation
– ambliopia - decreased vision in one eye
• sometimes called “lazy eye”
• stimulus deprivation ambliopia - from patching before 2 1/2 years of age
– stabismus - muscle imbalance
• sometimes called “wandering eye” or cross-eyed
– loss of stereopsis and loss of binocular cells
– critical period up to two and one half years
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Human Equivalents
• Selective rearing
– astigmatism
– “fuzzy” lines in a particular orientation
– the “oblique effect” - loss of the ability to see lines in a certain orientation
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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Summing up the evidence
• What seems innate?
• What seems learned?
Sensation and Perception - learning_development.ppt © 2001 Laura Snodgrass, Ph.D.
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