Fig. 6. Contrast-response surfaces of a single male HSN cell showing faster temporal dynamics and higher spatial frequency tuning in the frontal portion of the receptive field. The thick gray line in each panel is an iso-velocity line at the preferred velocity, the optimal temporal frequency (TF) divided by the optimal spatial frequency (SF). (A) Data are from the frontal portion of the receptive field, azimuth=0°, elevation=60°. (B) Data are from the lateral portion of the receptive field, azimuth=90°, elevation=60°. Height of surface is the estimated response to a grating of Michelson contrast 1.0 based on fit parameters calculated at each spatial and temporal frequency. Fit parameters for A are shown in Fig. 5. Contour interval=1.0 mV, with negative responses dotted.