Psychology 4051 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.