Fig. 6.

Developmental changes in center/surround interactions as a function of center stimulus contrast. (a) Center/surround interactions in representative units from V1 (Upper) and V2 (Lower) of an adult monkey. Contrast-response functions are illustrated for center only (red), center plus isooriented surround (blue), and center plus orthogonal surround (black). Responses are fitted into a hyperbolic function [R = R_{mC[supi]n/(C50[supi]n} + Cⁿ), in which C is the stimulus contrast, R_m is the maximum response, C₅₀ refers to the stimulus contrast that elicits half the maximum response, and n, the exponent, signifies the rate at which response changes occur]. (b) Contrast-dependent center/surround interactions in infant and adult monkeys. (Top row) Normalized responses of V1 neurons as a function of center contrast for center only (red), center plus isooriented surround (blue), and center plus orthogonal surround (black). Surround contrasts were kept at 80%. The representative unit for each age group was chosen based on the median value of n, C₅₀, and R_m of hyperbolic functions. (Second row) Differences (center/surround responses) between center only and center plus isooriented surround (filled circles) or between center only and center plus orthogonal surround (filled triangles). Positive values indicate facilitative center/surround interactions, and negative values indicate inhibitory interactions. (Third row) Comparable functions for representative V2 units as a function of age. (Bottom row) Comparable difference functions for V2 units.