Quantification and Comparison of Cell Properties in Cat's Striate Cortex Determined by Different Types of Stimuli.

Direction and orientation tuning elicited by moving bars, flashing bars and a moving noise field were compared in cells in area 17 of the cat. Fourier analysis of tuning curves (SDO-analysis) was applied to quantify the general sensitivity (S) to visual stimulation, tuning strength to direction(D) and orientation (O), as well as the preferred direction (PD) and orientation (PO). Results from SDO-analysis were compared with the commonly used direction index and half-width-at-half-height orientational tuning parameter and it is demonstrated that the commonly used parameters can be replaced and are superseded by the results from SDO-analysis. The comparison of the responses elicited by the different types of stimuli showed that a linear correlation between D (or O) components was mainly found in simple cells, while in most cases no correlation was obtained for complex cells. Since several of the simple cells also showed no linear relationship, a direct mutual prediction of the S, D and O components can only be achieved for approximately 50% of the cortical cells applying commonly used stimulus types. The general responsiveness (S) shows that flashing bar stimuli are at least as effective as moving bars, whereas moving noise stimulates cortical cells more weakly. A moving bar tends to increase the orientation tuning (O) in most cells and with a moving noise stimulus predominantly the directional tuning (D) of complex cells is strongly enhanced. In conclusion, Fourier analysis of tuning curves (SDO-analysis) provides a valuable and simple tool for the quantification of direction and orientation specificity. Motion enhances the cortical response specificity which indicates the involvement of facilitation or inhibition exclusively induced by movement.