The spatial organization of the excitatory regions in the visual receptive fields of the pigeon's optic tectum.

The spatial location of the excitatory regions in the receptive field of cells in the pigeon's optic tectum was analyzed with light and dark edges moving at a constant velocity. The tectal cells were classified into two main groups: 1-cells showing spatially overlapping light and dark excitatory regions in their receptive field (60%); cells showing spatially separated light and dark excitatory regions in their receptive field (32%). A small number of cells discharged only to one sign of contrast. These results were confirmed by testing the cells with light bars of various widths. Latency studies were carried out with single edges moving at a series of constant velocities. In most cases, for any given cell the light and dark edge discharges were shown to have similar latencies. These results also indicate that the relative location of the excitatory regions in the receptive field of most tectal cells was not significantly affected by the latency of the discharges.