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11 Cards in this Set

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Objective

Describe the effects of early lack of stimulation of one eye or both eyes.
If an experimenter sutures one eyelid shut for a kitten’s first four to six weeks of life, synapses in the visual cortex gradually become unresponsive to input from the deprived eye. Consequently, even after the deprived eye is opened, the kitten does not respond to input. If both eyes are kept shut for the first few weeks, we might expect the kitten to become blind in both eyes, but it does not. Evidently, when one eye remains shut during early development, the active synapses from the open eye displace the inactive synapses from the closed eye. If neither eye is active, no axon displaces any other. For at least three weeks, the kitten’s cortex remains normally responsive to both eyes. If the eyes remain shut for longer periods of time, the cortical responses become sluggish and lose their sharp receptive fields. That is, they respond to visual stimuli, but not much more strongly to one orientation than to another.
Objective

Explain how to restore sensitivity to an eye that has become inactive.
A kitten that has one eye closed for a period of several weeks recovers better if it goes through a few days with the opposite eye deprived of vision. Evidently, the deprived eye regains more cortical functioning if it doesn’t have to overcome a competitor.
Objective

Identify the characteristics of astigmatism.
Astigmatism is a blurring of vision for lines in one direction (e.g. horizontal, vertical, or one of the diagonals). It is caused by an asymmetric curvature of the eyes.
Objective

Discuss the visual impairments of people born with cataracts in either one eye or both eyes.
People born with cataracts (cloudy areas on the lenses) in one eye develop nearly normal vision, but problems do arise if the left eye is affected. As previously mentioned, prosopagnosia is linked most strongly to damage to the fusiform gyrus in the right hemisphere. This hemisphere needs early stimulation in order to develop its particular expertise at face recognition.
Objective

Summarize the case of patient MM.
When patient MM was 3 ½, hot corrosive chemicals splashed on his face, destroying one eye and obliterating the cornea of the other. For the next 40 years, he could see only light and dark through the surviving eye, with no patterns. He had no visual memories or visual imagery. At age 43, he received a corneal transplant. Immediately, he could identify simple shapes such as a square, detect whether a bar was tilted or upright, state the direction of a moving object, and identify which of two objects was in front of the other. These aspects of vision were evidently well established by age 3 ½ and capable of emerging again without practice. However, his perception of detail was poor and did not improve. Because his retina was normal, the failure to develop detail perception implied a limitation in his visual cortex. Over the next two years, he improved in his ability to understand what he was seeing but only to a limited extent.
binocular input
Stimulation from both eyes
sensitive (critical) period
Period when experiences have a particularly strong and long-lasting influence
retinal disparity
The discrepancy between what the left eye sees and what the right eye sees
strabismus
A condition in which the eyes do not point in the same direction
lazy eye
A condition that results from strabismus, in which a child fails to attend to the vision in one eye
astigmatism
A blurring of vision for lines in one direction (e.g. horizontal, vertical, or one of the diagonals)

Caused by an asymmetric curvature of the eyes