We
need to distinguish between sensation and perception. Sensation is the "rawÓ stimulation from your senses. Perception is your ability to detect
patterns in the raw stimulation.
That sounds like a car.
That looks like a Robin.
That feels like corduroy.
That smells like an onion.
How
do we study infants? It's
impossible to ask them to fill out questionnaires, we can't ask them what they
think, we must rely on other means.
Give
an infant a choice of two visual stimuli, and see which one the infant looks at
longer.
In a
habituation paradigm, the baby is presented with a stimulus over and over again
until the baby gets bored (stops looking, presentation of the stimulus doesn't
change respiration or heart rate).
Then a new stimulus is presented to see if the child dishabituates (pays
attention for a longer period of time).
The advantage of the habituation paradigm is that it can be used with
olfaction, hearing, tactile experiences, and taste as well as visual
stimuli. While this is a good
idea, this paradigm is also fraught with limitations. We must always be inferring the baby's thoughts. In addition, babies will spontaneously dishabituate to habituated
stimuli with time. Remember that
stimuli are complex. Example: Color (do babies really respond to
color, or simply to contrast)?
If a
baby detects some stimuli, then this information should be processed in a
particular portion of the baby's brain.
Once the baby is aware of the stimuli, we should be able to identify
changes in the baby's EEG.
Recall
that in operant conditioning, behavior on the part of the organism produces
some outcome in the environment (typically a reward or a punishment). Babies can be trained to look to one
side or the other, or to suck faster or slower. Remember that babies are born with a sucking reflex. Babies actually have a surprising
amount of control over their sucking behavior, it's something they're quite
good at from birth; as opposed to limb coordination, which they're not very
good at. Some researchers explore
infant preferences with an electronic pacifier that makes it easy to tell if
the baby is sucking faster or slower.
Babies can then be given the option of having access to particular
stimuli depending on whether they suck fast or slow (or stop). It's sort of like a baby operated
push-button. For example, suck
fast and the baby will hear its mother's voice, suck slow and you hear another
female voice.
Babies
are born with all the basic human sensory capacities. That is they are able to receive and respond to information
from all of the senses. While
infants are born with these sensory capabilities, they have to develop
perception skills. That is they
have to develop the ability to organize and to interpret sensory
information. They have to develop
the ability to give sensory input meaning. Ex: shapes,
babies don't see a difference until 7 months in the square habituation study
(overhead).
The
best research on sensory capacity in children is children's visual
ability.
Infant's
visual systems are functional at birth.
They can see objects directly in front of them, and they also possess
peripheral vision. They can
distinguish basic colors, and they can dilate their pupils to let the right
amount of light in. However, their
ability to focus is not so hot.
They can clearly see objects 8 to 20 inches away, but any closer or any
further and objects become blurry.
Marshall
Haith (1980) University of Denver.
Equipment for tracing the eye movements of newborns in light &
darkness. Infants scan better in
the dark, so put newborns to sleep in lighted room. Mobiles need to be visible
for babies, not adults.
For
newborns, perception will begin to develop quickly, by 6-7 months infant vision
is pretty sophisticated (perceive shapes, contrast sensitivity is better,
etc.).
Babies
scan better in the dark, they prefer to repeatedly scan edges, clearly, there's
no meaning for them in what they see!
They don't look at the triangle, they simply scan the first edge they
come to. What's going on? Haith: "The newborn's visual scanning activity is adapted to
keep the firing rate of visual cortical neurons at a high level." The child scans in a manner which
provides maximal stimulation.
She's practicing using her eyes in the only manner which is meaningful
to her. This practice of sensory
skill is going to lead to perceptual ability.
Yonas
has found that 7-month-olds reliably reach towards perceived pictorial cues,
while 5-month-olds do not. Campos,
visual cliff, 2 months, heart rate deceleration on deep side (suggests
interest). This suggests that
babies are able to detect depth at 2 months. However, no fear until 6-8 months. Locomotor experience is important. What factors might account for infants' sudden fear of
heights? a. Calibrate (judge distance) b. fall memory (falling sucks) c.
mothers emotional response (look out Johnny! You're going to fall!). Refusal to cross is interpreted as a fear of heights.
At
one month of age, when presented with a picture of mom's face, scan hairline a
high contrast area, looking at edge.
By two months of age the child is looking at more significant features
like the eyes. By 5 months the
face is becoming a meaningful object to the child, not just a set of
edges. Babies show a "social
smileÓ at around 3 months of age.
They will routinely smile in response to seeing their caregiver's
face. This is a very big
reinforcer for parents, it makes childcare a lot more rewarding.
Babies
must develop their contrast sensitivity.
Initially their vision is very blurry. See overhead.
Fantz
discovered that babies preferred looking at patterned stimuli. But it was the existence of high
contrast areas that was drawing their attraction, not a perception of the
pattern itself. For example, when
Fantz scrambled facial features, babies continued to look at the stimulus (only
for a slightly shorter period).
Preference for "realÓ rather than scrambled faces doesn't emerge until
2-3 months.
Not
really fast movement, they're not that good at tracking. They're better at perceiving slowly
moving objects than stationary ones.
As the months go by, babies can use motion data to determine objects. When you look into space, how can you
tell what is separate and what's part of everything else? An easy way to identify discrete
objects is if items move together at the same speed in the same direction. Babies can also use shapes and
continuation of lines to determine discrete objects.
A
checkerboard is preferable to a blank page or something very busy like
newsprint.
The
fetus is able to hear even before birth.
Although it's probably like being in a swimming pool. Unlike sight, hearing is a very passive
process, you don't have to tell your ears where to scan, you don't have to
focus them or anything like that.
That's probably why people say they have died and have been in the
operating room, and they come back to life & tell about it. Preference for mothers voice
(newborn). Muscle activity
indicates a preference for human voice 3- to 8-day-olds.
Recall
that early in life we actually lose neurons as the brain adapts to different
types of stimulation. Language
provides and excellent example of this.
The difference between "rÓ and "lÓ is readily apparent to people who
speak English. But those who are
raised in an environment where Japanese is spoken never hear this
distinction. As a result, if a
native Japanese speaker tries to learn English as an adult, he or she will find
it difficult to distinguish r and l sounds.
Babies
are particularly good at identifying their mother's voice. They are not equally good at
identifying their father's voice.
Decasper & Spence (1986) had mothers read "The Cat in the HatÓ
during their pregnancies. Babies
preferred to listen to the same stories they had heard in the womb rather than
novel stories.
Rooting
reflex, grip, etc. suggest that infants have good sense of touch. Smells: babies show a preference for mothers' breast pads at 1-2
weeks. Also, newborns show a
preference for strawberries and bananas vs. rotten eggs and fish even before
child has eaten anything! Taste:
preference for sweet solutions.
Amazing that even at birth infants possess remarkable sensory
capabilities.