Visual detection of aperiodic spatial stimuli by probability summation among narrowband channels

Recent psychophysical results of Shapley and Tolhurst and of Kulikowski and King-Smith have suggested that the visual system contains broadband channels like “edge detectors” and “line detectors” as well as relatively narrowband “spatial frequency” channels. These recent results (including thresholds for aperiodic stimuli) can be completely explained using only relatively narrowband channels with probability summation among them. This explanation requires many fewer free parameters than the original explanation based on both broadband and narrowband channels. The bandwidths of the individual narrowband channels can be estimated and are similar to those previously estimated from sine-wave summation experiments.