Abstract
Synchronous firing of directionally selective (DS) cells in the rabbit retina is stimulus dependent (Amthor et al., 2005, in press). Millisecond time-scale correlation is strongest for responses to the movement of bars that simultaneously cross the receptive fields of two DS cells. In contrast, although these cells respond with similar time courses to full-field stimulation, they do not exhibit significant millisecond correlation. Here, we extend the study to all classes of ganglion cell using multi-electrode array recordings. Cells were identified and automatically classified using full-field luminance steps, and moving bars and edges. Responses to full-field luminance steps did not show significant millisecond time-scale correlation within or across any cell classes. However, movement of extended bars that simultaneously crossed the receptive fields of neighboring cells often generated significant correlation. This occurred both within and across cell classes. The temporal structure of the correlations had a positive component flanked by negative components. This structure varied depending on the cell types and stimulus features Interestingly, for some pairs of non-DS cells these correlations were direction dependent. In conclusion, we find strong ganglion-cell correlations in response to extended edges, but not to full-field luminance steps. We interpret this as a possible code to indicate the contour of a single object as opposed to its interior. We hypothesize that the directional dependence seen in the correlation of some cells is not a true ‘directional’ signal, but is a result of the geometry of their receptive field relative to the orientation of the contour.
The work was supported by National Institute of Health Grants EY11170 and EY08921 to N.M.G.