Calibration of a Spatiotemporal Discrimination Model from Forward,Simultaneous,and Backward Masking

Abstract

We have been developing a simplified spatiotemporal discrimination model similar to our simplified spatial model in that masking is assumed to be a function of the local visible contrast energy. The overall spatiotemporal sensitivity of the model is calibrated to predict the detectability of targets on a uniform background. To calibrate the spatiotemporal integration functions that define local visible contrast energy, spatiotemporal masking data are required.

Observer thresholds were measured (2IFC) for the detection of a 12 ms target stimulus in the presence of a 700 ms mask. Targets were 1, 3, or 9 cycles deg⁻¹ sine-wave gratings. Masks were either one of these gratings or two of them combined. The target was presented in 17 temporal positions with respect to the mask, including positions before, during, and after the mask. Peak masking was found near mask onset and offset for 1 and 3 cycles deg⁻¹ targets, while masking effects were more nearly uniform during the mask for the 9 cycles deg⁻¹ target.

As in the purely spatial case, the simplified model cannot predict all the details of masking as a function of masking component spatial frequencies, but overall the prediction errors are small.