The observation that the response t o the second of two stimuli is delayed if a response has to be made to the first has led t o the development of a theory of a central refractory state during which incoming stimuli cannot be elaborated. In the experiment reported here the two stimulus-response situations have been made as independent as possible, and under these conditions it is shown that this theory cannot be maintained in its present form. The concept that the central integrating mechanism readily becomes blocked by nay single stimulus is dismissed as nonproven and uneconomic. The present findings, however, confirm previous observations that some interference between the two situations may occur b u t indicate that this is not necessarily maximal immediately after the presentation of the first stimulus. I t is tentatively suggested that the phenomena of central inhibition can be interpreted in terms of the interaction between the excitatory and inhibitory significance of the stimuli and the internal anticipatory set. INTRODUCTIONMuch controversy in the early literature on the psychology of sldled movements centred round the discussion a s to whether attention could be divided between two skilled tasks (Woodworth 1938). Nost authorities favoured the view that such a division of attention was in fact impossible. I t was held that where simultaneity of performance was apparent this was achieved by a rapid alternation o i attention between the two tasks. Ryle, who is not addicted to dichotomies-in this case "all tasks must be either attended to or not attended to"-has pointed out that this difficulty may be largely a verbal one. He believes that the concept of heed or attention belongs to that class of dispositional statements which is both categorical

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Previous experimental work has suggested that bilateral reaction times to visual stimuli may be wbject to dominance effects, and that where pairs of stimuli are closely ordered in time, these effects may be more complex than a simple superiority in speed of performance by the dominant hand. Twenty subjects, ten markedly left handed and ten markedly right handed, were selected from a larger group of forty-four subjects to examine these effects in detail.Results showed:(1) For single responses and paired responses to simultaneous stimuli, responses by the dominant hand were made significantly faster than by the non-dominant hand.(2) A reversal of this effect occurred with the second responses to paired stimuli which were separated by an interval of 100 msec., the dominant responses being made significantly more slowly than the non-dominant responses.(3) This reversal was a feature of the delayed responses only, i.e. of those responses where reaction time t o the second stimulus was lengthened following a response to the first stimulus. Where the response to S 2 was not delayed, dominance effects were in the same direction as for the single responses.(4) A subsidiary finding was that, apart from the relative magnitudes of response times, types of response to paired stimuli showed some relationship to individual dominance. I n particular the response to S 2 was more often delayed in the stimulus order non-dominant/dominant than in the opposite order and responses were more often made independently in the order dominant/ non-dominant.

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