A correlational model for the
development of disparity in visual cortex that depends on
prenatal and postnatal phases.
Greg Berns Peter Dayan Terry Sejnowski
Proceedings of the National Academy of Science (USA),
90, 8277-8281.
Abstract
Neurons in the visual cortex require correlated binocular activity
during a critical period early in life to develop normal response
properties. We present a model for how the disparity selectivity of
cortical neurons might arise during development. The model is based on
Hebbian mechanisms for plasticity at synapses between geniculocortical
neurons and cortical cells. The model is driven by correlated activity
in retinal ganglion cells within each eye before birth and
additionally between eyes after birth. With no correlations present
between the eyes, the cortical model developed only monocular
cells. Adding a small amount of correlation between eyes at the
beginning of development produced cortical neurons that were entirely
binocular and tuned to zero disparity. However, if an initial phase of
purely same-eye correlations was followed by a second phase of
development that included correlations between eyes, the cortical
model became populated with both monocular and binocular
cells. Moreover, in the two-phase model, binocular cells tended to be
selective for zero disparity, whereas the more monocular cells tended
to have nonzero disparity. This relationship between ocular dominance
and disparity has been observed in the visual cortex of the cat by
other workers. Differences in the relative timing of the two
developmental phases could account for the higher proportion of
monocular cells found in the visual cortices of other animals.