Fig. 2: Impaired contour detection performance after V4 inactivation.

a Contour detection task. The monkey fixated on a small spot (left) until the onset of the stimulus pattern (middle and right), which consisted of small bars (0.25° × 0.05° for MA, 0.2° × 0.04° for MB) distributed in a grid of 13 × 13 invisible square compartments (0.5° for MA, 0.4° for MB). The stimulus included randomly oriented background bars, with a contour formed by collinear bars either present (upper row) or absent (lower row). The monkey was required to make a saccade to the contour within 500 ms (Go trials) or maintain fixation (No-go trials). The contour was offset by one row in the invisible grid (upper right), so rotating the circular pattern around its center varied both the position and orientation of the contour. The contour position was fixed for each day, and a total of 8 contour positions were tested on separate days by rotating the stimulus in multiples of 45°. For each position, the contour in the Go trials could be one of 4 lengths (3, 5, 7 or 9 collinear bars) with equal probability. b–d Behavioral results from monkey MA. Contour detection performance (behavioral d^′) is plotted as a function of contour length in the cooling experiment (b) and the sham-cooling control experiment (c). Each data point on the curve represents the average across the 8 contour positions (i.e., n = 8; see a legend). The overall changes in d^′ after V4 cooling (ΔCool) and sham-cooling (ΔSham) were calculated, respectively, relative to the pre-cooling and pre-sham sessions by averaging across the 4 contour lengths and 8 contour positions (d, n = 32, p = 3.0 × 10⁻⁵, two-tailed Wilcoxon signed-rank test). e–g Similar results from monkey MB (e, f, n = 8; g, n = 32, p = 1.4 × 10⁻⁶, two-tailed Wilcoxon signed-rank test). Error bars represent SEM; ***, p < 0.001. Source data are provided as a Source Data file.