Determination of the receptive field center measured by two types of electrodes. A) the RF center measured by the S-E through the distribution of the gamma oscillations PSD by systematically placing a narrow drifting grating patch at different positions along axes perpendicular or parallel to the optimal orientation. B) the RF center measured by the T-E through the distribution of the gamma oscillations PSD by systematically placing a narrow drifting grating patch at different positions along axes perpendicular or parallel to the optimal orientation. Error bars are SEM.