Fig. 5.

Structure of neural correlations depends on stimulus position. The structure of pairwise spike count correlations (“noise correlations”) from different perspectives. Data represent all pairs of responsive sites where the stimulus was moving in the preferred direction of both sites (n = 967,980). Receptive field (RF) positions are expressed in SD of a Gaussian fit to each site's spatial-response profile. Stimulus positions preceding the receptive-field center are indicated as negative values and vice versa for stimulus positions after passing through the receptive-field center. Shading of bar in C applies to A–C. A: noise correlation is higher for pairs of receptive fields with greater overlap. Left: average noise correlations collapsed across stimulus positions as a function of the distance between receptive fields (ΔRF), normalized by the geometric mean of their SD. Right: the correlation structure on the left can be projected into a joint space, defined by the position of a stimulus within 2 receptive fields (RF1 and RF2). The shading of the image indicates the strength of noise correlation that is predicted by the data on the left. B, left: noise correlation as a function of the response rate of each neuron. Average noise correlations were collapsed across stimulus positions. Right: the spiking rate was mapped to receptive-field positions using the average spatial response profile and the result projected onto the joint space, defined by the position of a stimulus within 2 receptive fields. The shading of the image indicates the strength of noise correlation that is predicted by the data on the left. C: joint space defined by the position of a stimulus within 2 receptive fields (RF1 and RF2). The shading of the image indicates the strength of noise correlation measured at each stimulus position. The rich structure is similar to that predicted by the combination of A and B. D: population activity was simulated multiple times using multivariate, normal distributions. In each simulation, the mean activity of neurons was that measured, and the correlation matrix was preserved everywhere except within 1 partition, where the correlation coefficient was halved. E: impact of decorrelation on spatial discrimination depends on the masked partition. Shading indicates the relative impact of decorrelation on capacity to discriminate 1° change in stimulus position: darker shades indicate where attenuating correlations reduced performance and lighter shades, where attenuating correlations improved performance.