Pattern detection: interactions between oriented and concentric patterns.

Target threshold vs. pedestal contrast (TvC) functions for a vertical and a concentric target were measured on a vertical, a horizontal, a plaid or a concentric Gabor pedestal. All patterns had Guassian envelopes. All except one of the TvC functions had a dipper shape, that is, the target threshold first decreased and then increased with the pedestal contrast. The TvC function for a vertical target on a horizontal pedestal was monotonically increasing. A divisive inhibition model with two orientation selective mechanisms, sensitive to vertical and horizontal, fits the data reasonably well. A significant improvement in fit is obtained by adding one or two more mechanisms. These additional mechanisms are different for different observers. Some are consistent with oblique receptive fields, some with concentric receptive fields, and some are indeterminate.