Figure 3.

Population responses during physical alternation and binocular flash suppression conditions. Before averaging, conditions were sorted to preferred (P) and nonpreferred (N) according to the responses during the monocular period of presentation. Plots in A and B depict average spike density functions for all physically selective neurons (n = 371). The upper part of the figure shows a diagram of the different conditions. A vertical grating is marked with P (preferred) and a horizontal with N (nonpreferred) for reasons of clarity. In essence, any one of 8 different orientations could be preferred with its orthogonal being the nonpreferred. The black dots in the binocular period denote the grating which was perceived. In A, the mean time courses of the population activity under the physical alternation conditions are presented. Dark solid lines represent the mean spike density functions for a presentation sequence of preferred (0–1000 ms) followed by the nonpreferred (1000–2000 ms) grating. Light gray solid lines represent the mean spike density functions for a presentation of the nonpreferred grating first, followed by the preferred. Shaded areas around the lines represent SEMs calculated over the neurons averaged. In B, the mean population time courses for the binocular flash suppression conditions are plotted in a similar manner. In C, D, the average differences between the preferred and nonpreferred conditions are depicted for the same populations of cells for the physical alternation (C) and flash suppression (D). Modulations are expressed as a percentage of the maximum modulation during the monocular presentation (0–1000 ms). The dotted line in D is a copy of the physical alternation modulation in C to provide a means of direct comparison with the perceptual modulation during flash suppression.