Abstract
Purpose: :
To understand the basis of poor performance by young infants in contour integration tasks, we studied the ability of extrastriate cortical neurons (V2) to integrate oriented contours or texture elements over extended space. In adult monkeys, we previously found that stimulation of small, restricted regions of receptive field surround facilitates the RF center responses of V2 neurons while other regions suppress the center responses depending on the location and the orientation of surround patches, which suggested that V2 neurons may be able to encode colinearity and/or angles sustained by multiple contour elements that extend way beyond the RF center of V2 neurons. In this study we investigated the postnatal development of such facilitatory surround effects in V2 neurons of anesthetized monkeys ranging in age between 4 and 16 weeks.
Methods: :
A pair of surround patches, matched in size for the unit’s RF center stimulus, was presented across the RF center at 4 different locations. After determining the optimal location for surround facilitation for each unit, the orientation of surround patches were varied in relation to that for the center stimuli for 0, 45, 90, and 135 degrees.
Results: :
With respect to the position of surround stimuli, the adult-like pattern of facilitatory surround effects (optimal for the top/bottom position) did not emerge until 16 weeks of age. Also the optimal facilitatory effects of surround patch orientation (co-linearity) at the top/bottom position did not become adult-like until 16 weeks of age.
Conclusions: :
These results suggest that the functional connections supporting the local regions of RF surround in V2 neurons are considerably immature before 16 weeks of age, and that the inability of low-level extrastriate visual neurons to accurately pool local stimulus feature information over extended space may impose limits on the development of the perceptual decision-making mechanisms downstream.
Keywords: visual cortex • development • electrophysiology: non-clinical