Figure 1.

Sample orientation tuning curves from drifting grating stimuli: (a) Experiment (three 4Cα simple cells). The response is measured as time-averaged firing rate and is plotted in units of impulses per sec. Stimuli were at optimal temporal frequency for each neuron, 2−10 Hz). (b) Model (excitatory neurons, 8 Hz). The model results also include the orientation selectivity obtained by an uncoupled neuron (long-dash line, the “feed-forward response”), normalized for comparison to a peak response of 40 spikes per sec. As shown, some of the model's neurons may be directionally selective (dashes), as are some 4Cα cells.