Development of visual stimulus-seeking in dark-reared kittens

Abstract

EARLY visual experience is important for the development of vision in kittens. The response specificity of visual neurones for different environmental features can be affected by selective visual exposure to those features, and leads to long term changes in visual capacities^1–4. Modification occurs only if the kitten is exposed selectively during the first three months of life. The peak period of sensitivity for “tuning” seems to occur between days 28 and 35, and thereafter declines rapidly; by the end of the second month, neuronal connections are less readily modifiable^5–6. The peak of the sensitive period coincides with the clearance of the ocular media⁷, the beginnings of adequate locomotor control (M. S. Levine, C. D. Hull, and N. A. Buckwald, unpublished), completion of the most active phase of myelination in the optic nerve and optic tract (C. L. Moore, R. E. Kalil, and W. A. Richards, unpublished), and the period of greatest synaptic density in the visual cortex⁸. In the present study we show that kittens do not spontaneously seek light at this time. Rather, there is a sudden onset of light-seeking behaviour at two months of age, when the cortical contour-coding system is not very sensitive to environmental modification, and many other adult visual characteristics have already been acquired.