Sokolov placed attentional and response requirements in the same dimension of stimulus “significance,” and proposed that these produced similar effects upon the magnitude and habituation rate of the OR. In a previous study, subjects were required to focus attention on stimulus events; here, the same stimuli served as imperative signals in a simple RT task. The effect of this manipulation upon several indices of the OR (GSR, respiration, HR, PPV, CPV, and EEG) failed to support Sokolov’s position. The data obtained were used to further develop a hypothetical structure tentatively offered as a replacement of the unitary OR concept. © 1978, Psychonomic Society, Inc.. All rights reserved.