Correlations between directional and orientational tuning of cells in cat striate cortex

Simple (N = 284) and complex cells (N = 125) in the central projection area (0-5 degrees eccentricity) of the striate cortex of cats were stimulated with moving light bars and the responses to different directions of movement were recorded and plotted as polar-plots. Fourier analysis was applied to polar plots (SDO-analysis, Wörgötter and Eysel 1987; Wörgötter et al. 1990) to determine the general sensitivity (S) of the cells to visual stimulation, the directional (D) and orientational (O) tuning strength as well as preferred direction (PD) and preferred orientation (PO). Statistical distributions of the S, D and O parameters were determined for simple and complex cells of the cortical layers II-VI. Simple cells were more strongly tuned for direction and orientation than complex cells, whereas complex cells had a greater general sensitivity to visual stimulation. Directional tuning was significantly stronger in layer VI than in layer IV simple cells, otherwise no differences were detected between these two layers. We found that cells with large D and small O components are generally rare. The D and O components were plotted against each other to determine any possible correlation between the tuning strengths. The correlations were statistically significant for simple and complex cells but the correlation coefficients were very small (r less than 0.3). It is suggested that only a very weak coupling between directional and orientational tuning exists, preferentially in the deeper layer simple cells.