A dominant-subordinate unit-against-unit theory of decreases in visibility.

When simultaneous stimuli or stimuli in metacontrast and related research are perceived (recognized, apprehended) as two different phenomenal groups (wholes, things), the visibility of the group with less intense, smaller, no-onsetting, terminating, and briefer features decreases. This decrease also occurs when one of two groups with equally intense, etc. features is made less visible through masking. Therefore, the relative visibility of two groups predicts a decrease in the visibility of one of them better than does their relative intensity, etc. Further, (1) the visibility of all the parts (perceived features, attributes) of both groups is similarly affected, so each group functions as one entity and (2) decreases in visibility are eliminated when stimuli produce only one group. The theory: a neural unit underlies the perception of one group and its parts, and two such units underlie the perception of two groups and their parts (one unit for each group). In addition, the unit for a dominant (high visibility) group inhibits the unit for a subordinate (low visibility) group, thereby decreasing the visibility of the subordinate group. Also, when stimuli produce only one group (hence one unit), unit-against-unit inhibition and hence a decrease in visibility is precluded.