Sokolov’s conceptualization of the OR has many elaborations reflecting its postulated importance in perceptual and motor processes, but in the final analysis its validity rests on the reality of the physiological processes which are hypothesized to occur in response to simple stimuli. These are supposed to behave in a coherent manner which allows the use of the term “OR” as a unitary concept. Such an OR is hypothesized to depend on stimulus intensity, novelty, and significance in well-defined ways. This study focused upon the last variable as manipulated by attentional demand. The small effects obtained by this manipulation were not as predicted by Sokolov, and were able to be explained most parsimoniously in terms of novelty. These results generated a new hypothetical structure tentatively offered as a first step in the replacement of the unitary OR concept. © 1977, Psychonomic Society, Inc.. All rights reserved.