Population coding of motion patterns in the early visual system

Using extracellular recordings and computational modeling, we study the res ponses of a population of turtle (Pseudemys scripta elegans) retinal gangli on cells to different motion patterns. The onset of motion of a bright bar is signaled by a rise of the population activity that occurs within less th an 100 ms. Correspondingly, more complex stimulus movement patterns are ref lected by rapid variations of the firing rate of the retinal ganglion cell population. This behavior is reproduced by a computational model that gener ates ganglion cell activity from the spatio-temporal stimulus pattern using a Wiener model complemented by a lion-linear contrast gain control feedbac k loop responsible for the sharp transients in response to motion onset. Th is study demonstrates that contrast gain control strongly influences the te mporal course of retinal population activity, and thereby plays a major rol e in the formation of a population code for stimulus movement patterns.