Figure 3.

Ganglion cell temporal STAs are composed of subfilters with five distinct patterns of spatiotemporal tuning. (A) The average temporal STAs (black traces) within annuli at different radial distances from the receptive field center (see Fig. 2) were each fit by the sum of up to three subfilters (brown/orange traces). Each subfilter is the impulse response of a low‐pass temporal filter. Annular distance is indicated by the primary‐colored bar at the top, with central annuli on the right. (B) Comparison of subfilter properties from all annuli: amplitude (|p|), delay to peak (τ), and filter order (n). Subfilters are divided into center and antagonistic groups based on their polarity relative to the receptive field center. Colors are carried from (A) to illustrate how the subfilter population is obtained. (C) The same plot, recolored into five subfilter types (pastel colors) based on a three‐dimensional (p, τ, n) mixture of Gaussians clustering. Clusters were identified as center or surround based on D and E. (D) The same cell from (A) is shown with its component subfilters colored by the types from (C). Center subfilter types 1 (magenta), 2 (orange), and 3 (green) are located in the central annuli, whereas surround subfilter types 1 (purple) and 2 (gray) are in more distant annuli. (E) The dependence of subfilter type on radial distance is illustrated by breaking plot (C) down by radial distance and combining both polarities. (F) The subfilters from (C) have been recolored by their radial distance from center to demonstrate the dependence of subfilter properties on radial distance. Bordered regions have been added to approximate the boundaries between the subfilter types shown in (C). Within each subfilter type, there is a strong dependence of p on radial distance (vertical rainbow effect in the bottom plots), but no obvious codependence for τ or n. This indicates that individual subfilter types vary their scale but maintain their shape over space, suggesting they are space–time separable.