The responses of our developed V1 cells are tested with careful simulations which include both the feedforward connections and the feedback connections. It is important to understand that in our model (as in the real experiments) the orientation selectivity of V1 cell are highly context dependent, i.e., not only the stimuli within the receptive field influence the response, but also the surrounding stimuli outside the feedforward inputs area. This context dependency will be further studied in the Quantitative Comparisons ... section. Here, the cells responses are probed with simple stimuli.
Figure 3: The orientation selectivity of developed V1 cells. The stimuli are presented at varying orientation (at 10 degrees increments). The input stimulus contrast in the three curves is multiplied by 1.0, 0.75, and 0.5. The orientation tuning width remains unchanged, roughly 20 degrees.
The selectivity of developed V1 cells is shown in Figure 3. The stimuli are bars which are of length of the size of input area size and of width of 1/3 of the length. Responses of many V1 cells in one column are averaged to give the orientation tuning curves. While the response of the cortex decreases with decreasing stimulus contrast, the bandwidth remains virtually unchanged, in agreement with experimental data . This result is used in the Quantitative Comparisons ... section to do the comparison with experiments.
Many more simulations have been done to probe the response properties of our developed network with feedback connections. But we find that the most reliable experimental data which could be compared quantitatively with our model predictions are psychophysical experiments on orientation illusions. To do those comparisons only first order analyses are needed.