Physiological changes in a reaction time task: Further problems with Sokolov’s dimension of stimulus “significance”

Abstract

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. The orienting response (OR) of Sokolov (1963) may be described as a unitary response system sensi­ tive to stimulus variation in three dimensions: novelty, intensity, and significance. Upon this response system has been built, by Sokolov and others, an elaborate theoretical structure concerned with the psychophysiological basis of perception and attentive processes. Barry (1975, 1976, 1977a, 1977b) has critically examined the foundations of this theoretical structure by comparing Sokolov's detailed predictions regarding stimulus-response relationships with experimental findings from parametric inves­ tigations. These have centered upon six psycho­ physiological indices: electroencephalographic (EEG) alpha rhythm levels, galvanic skin response (GSR), heart rate (HR), respiration, and cephalic and peripheral pulse volumes (CPV and PPV, respec­ tively). Changes in these measures have been inves­ tigated as a function of stimulus intensity (using auditory stimulation of from 20 to 50 dB SPL), novelty (by providing repeated cycles of the stimulus complex), and significance (indifferent stimuli vs. instructions to attend). Barry (l977a) reported that the dependent variables listed above exhibited such markedly different behav­ iors in response to manipulation of stimulus intensity and novelty that the concept of a unitary OR appeared untenable: only two of the six measures examined covaried to the extent of having similar relationships with these two independent variables. It would thus appear that the simple OR concept which has been widely accepted in western psychophysiology may be an extreme oversimplification, having little empirical basis. Barry (l977b) varied stimulus significance,