Visual detection of signals in the presence of continuous and pulsed backqrounds

The detectability of intensity increments in the presence of continuous and pulsed backgrounds was investigated using a two-alternative, temporal, forced-choice procedure. Differences were found in intensity-duration reciprocity relations, the form of the Weber function, and the shape of the psychometric function between continuous- and pulsed-detection conditions. In a second study, signals were added either to a steady background (simple detection) or to background plus pedestal (pedestal detection). Two unusual phenomena were noted, namely, “negative masking” and the “pedestal effect.” The interpretation of the results in terms of a simple, Poisson-detection model is discussed.