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Keeping an eye on the brain: the role of visual experience in monkeys and children
M L Crawford1, R S Harwerth, E L Smith
1Sensory Sciences Center, University of Texas.
Insights
Early visual experience shapes infant primate vision development. Critical periods for visual functions vary, with binocular vision remaining sensitive to deprivation for up to two years, impacting stereopsis.
Area of Science:
- Neuroscience
- Developmental Biology
- Ophthalmology
Background:
- Infant visual experience is crucial for mature visual system development.
- Monocular form deprivation in infant monkeys reveals critical periods for visual development.
Purpose of the Study:
- To investigate the critical periods of visual development in infant primates.
- To understand the long-term effects of visual deprivation and abnormal visual experience on visual functions.
Main Methods:
- Monocular form deprivation in infant monkeys.
- Prism-induced visual experience mimicking strabismus.
- Assessment of visual functions including photopic and scotopic sensitivity, and binocular functions.
Main Results:
- A critical period for visual development lasts up to two years, with sensitivity decreasing over time.
- Photopic sensitivity has a critical period ending by 6 months; scotopic functions are developed by 3 months.
- Prism-induced strabismus permanently reduces cortical binocular cells and stereopsis.
Conclusions:
- Binocular visual functions have the longest sensitivity period to abnormal visual experience.
- Early visual deprivation and conditions like strabismus can lead to permanent visual deficits, explaining conditions like stereoblindness.
Abstract:
The quality of visual experience during infancy determines the functional sensitivity and precision of the mature primate visual system. Infant monkeys subjected to monocular form deprivation show a period of critical visual development that, though decreasing in sensitivity, lasts throughout the first 2 years of life. Photopic threshold spectral sensitivity appears to have a briefer critical period, which is essentially complete by 6 months old, whereas scotopic visual functions appear well developed by 3 months old. Binocular visual functions seem to have the longest period of sensitivity to abnormal visual experience because periods of monocular form deprivation initiated during the first 2 years affect visual functions. Viewing the world through prisms, which mimics the condition of strabismus, causes a permanent loss of cortical binocular cells and stereopsis in monkeys. This result explains stereoblindness in children having equivalent clinical histories.