Response of the SFA units with respect to phase and orientation of sinusoidal gratings.
A Responses to sinusoidal gratings depicted as a function of orientation (y-axis) and phase (x-axis) of the grating. The spatial frequency was set to the unit's preferred value. B Histogram of response modulation (F1/F0) values, indicating the susceptibility to the phase parameter of the input grating. Black bars correspond to using the full response of the units to compute F1/F0 values, white bars correspond to using the half-wave rectified response. This histogram is illustrates that most of the SFA units from this simulation run (45 out of 50) have an F1/F0 value smaller than one and would thus be classified as complex cells in a physiological experiment. It cannot be expected to resemble the distribution of simple and complex cells in visual cortex. C Histogram of orientation selectivity (OSI) values, indicating the susceptibility to the orientation parameter of the input grating. Black bars correspond to using the full response of the units to compute OSI values, white bars correspond to using the half-wave rectified response. D and E show OSI histograms obtained from ferrets (adapted with permission from Figure 2 of Chapman B et al. (1993) ). Eye opening occurs between postnatal week 5 and 6. See last paragraphs of the Results section for a thorough investigation of the reasons for high OSI values.