Widely separated spatial frequencies: mechanism interactions.

The question of independence between spatially tuned mechanisms that respond to very different frequencies is addressed by a theoretical reconstruction of their responses to single and compound grating stimuli presented at near-threshold levels. Parameters of sensory response distributions are estimated in a two-response rating experiment, and tested against those predicted by a Signal Detection model when independent processing is assumed. Small but consistent deviations from predicted values were observed and are interpreted in terms of frequency-specific patterns of inhibition and stochastic correlation. It is further demonstrated that these interactions may in part account for the superiority of discrimination over detection found with such widely separated frequencies.