ABSTRACTThe cardiac deceleration which occurs during the preparatory interval (PI) of a reaction time (RT) task was examined with reference to a facilitatory feedback model in contrast with a model which viewed the response as part of a somatic inhibitory response. Sixty‐three male Ss were run in three independent groups in an RT study. Two groups received 96 trials (divided into blocks of 24) with PIs of 2, 4, 8, and 16 sec presented in a regular series counterbalanced for order. The third group received the same number of trials of each PI in a restricted random order. Heart rate (HR), chin electromyograph (EMG), eye blinks, and eye movements were recorded as dependent variables.Results indicated an orderly, time‐locked decline in EMG, eye blinks and movements, which was closely concomitant with a deceleration in HR during the PI. With some exceptions, the various measures demonstrated similar functional relationships with Group and PI variables. The results failed to differentiate between the feedback and somatic inhibitory models because the only combination of variables which eliminated HR deceleration also eliminated the inhibition of the somatic measures. This fact is consistent with the somatic inhibitory model, but is neutral with respect to the feedback model. Different statistical methods for examining the cardiac‐somatic concomitance were disc