On the nature of input channels in visual processing.

The research reported herein was designed to assess whether the presence of noise elements in a visual display affects the detection of target letters at the perceptual or feature extraction level of processing, as well as at the decision level, and more specifically, whether (a) input or processing channels operate in an independent or interactive fashion and (b) how the spatial relation between signal and noise items affects detection performance. In order to distinguish among current theories proposed to account for the influence of noise items on visual processing, a forced-choice detection task was modified to incorporate a cueing procedure, which permitted the independent variation of signal-noise similarity, confusability, and proximity. The results provide evidence for feature-specific inhibition at the perceptual level, and a theory is proposed that assumes hierarchically organized, limited-capacity feature detectors and feature-specific inhibitory channels. There is now considerable evidence that the detectability of a designated signal is impaired by the presence of noise elements in the same visual display. The degree of impairment has been shown to vary as a function of the confusability of noise elements with the set of alternative targets (Estes, 1972; Gardner, 1973; Mclntyre, Fox, & Neale, 1970) and the spatial proximity of target and noise (Strangert & Brannstrom, 1975; Wolford & Rollingsworth, 1974). However, whether the effects of signal-noise similarity on target detection might be different than the effects of signalnoise confusability and how either of these variables might interact with signal-noise proximity has not been established; nor is it clear at what level of processing noise items impair the visual detection of signals. Evidence Edward E. Smith acted as Guest Editor for this article. The research reported was supported by Grant