Strength theories of disjunctive visual detection

Zero, 1, 2, or 3 black dots are tachistoscopically presented on a white field. There are two alternative tasks: (a) to decide on the presence of each of the left, middle, and right dots (multiple detection) or (b) to decide whether any of the dots was present (disjunctive detection), The results indicate that in disjunctive detection, Ss do not add together thestrengths of the three dot positions and compare this sum to a criterion. Rather they combine theirdecisions about each dot, responding “yes” to the array, if and only if they decide “yes” to any one dot. Strength distributions appear to be invariant with respect to irrelevant stimuli. Invariance with respect to report order holds approximately. However, dots reported on first are slightly more detectable. This suggests a successive scanning process, whose rate is independent of whether a stimulus is present or absent at the position scanned.