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Psychology 4051
Visual System
Plasticity
Visual System Plasticity
• The first decade of life represents a period of
substantial development of the visual system.
• This is also a period of plasticity during which
connections to the visual cortex are
susceptible to environmental insult.
• This period represents a critical/sensitive
period during which normal visual experience
is necessary for the formation of connections
to the visual cortex.
Visual System Plasticity
• Visual deprivation caused by visual insult can
impede the formation of these connections.
• During this time the eyes are in competition to
form cortical connections.
• Monocular visual deprivation can severely
impair connections from the deprived eye.
Animal Studies
• Hubel and Wiesel have conducted numerous
studies indicating that early visual deprivation
causes severe changes to the visual system.
• Cats and monkeys generally have an eye
sutured shut early in life.
– Animal undergo single cell recordings
• In animals, the critical period appears to be
between eye opening (or birth) and puberty.
Animal Studies
• The length of the visual deprivation and the
timing of the deprivation is very important.
– Longer deprivation is generally more drastic.
– But there are periods in which animals are
extremely sensitive even to short periods of
deprivation.
Anatomical/Physiological Effects
• There are no effects on cells in the retina.
• LGN cells corresponding to the deprived eye
are smaller but respond normally.
• Most of the effects are in the visual cortex.
• Overall, there is a decline in the number of
cortical cells driven by the deprived eye.
– Found in all cortical layers.
Anatomical/Physiological Effects
• Animals who are forced to use the deprived
eye later, often behave as though they are
blind.
• Researchers have also investigated the effects
of surgically-induced strabismus.
• Most cells in the visual cortex are monocular.
Treatment
• While in this period of plasticity some of the
effects of monocular deprivation can be
reversed by reverse suturing.
– Sewing the other eye shut to force the use of the
deprived eye.
• If done during the critical period, the deprived
eye regains cortical connections and acuity
improves.
Human Studies
• Researchers have investigated the effects of
naturally occurring deprivation in humans by
looking at children who had cataracts.
– Opacity on the lens that prevents the formation of
a sharp image.
• These studies confirm that the critical period
lasts from birth to 10 years.
Human Studies
• Longer periods produce more severe effects,
but timing is also important.
– Leads to poorer visual acuities.
• Early deprivation tends to produce drastic
effects.
• The effects of bilateral cataracts are far less
severe.
– Competition between the eyes is not
compromised.