ABSTRACT: Defines a relationship between stimulus and response of "ideomotor compatibility" as occurring to the extent that the stimulus resembles normally occurring sensory feedback from the response (e.g., saying a word in response to hearing it said). It is proposed that the stimulus of highly ideomotor-compatible combinations should effectively select the response without burdening limited-capacity decision processes of the CNS. Accordingly, (a) perfectly efficient time sharing of 2 simultaneous decision tasks was predicted when both tasks were highly ideomotor compatible, and (b) inefficient time sharing was expected when both tasks were not highly ideomotor compatible. 8 undergraduates served in high and 8 in low ideomotor compatibility conditions that required rapid independent decision responses (spoken and manual) to 2 simultaneous stimuli (auditory and visual). The predicted effect of the ideomotor-compatibility variation on time-sharing efficiency was clearly confirmed.