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.

No abstract

An improved version of a perceptual maze test, which has been shown to be sensitive to frontal and temporal lobe damage, is described. The present test possesses a fully binary structure and parameters describing the task are now more easily definable. An experiment is reported in which the effect of varying two of these parameters, size and density of pattern, was examined. In order to minimize differential practice effects, a 36 x 36 random Latin square design waa used, 36 normal subjects being tested with 36 patterns. The results show that the effect of the variation of these two parameters on the difficulty experienced by the subject in solving the teak is reilably pronounced.

When a subject is called upon to respond independently to two stimuli, the second of the two responses is often delayed if the stimuli follow closely on one another, and this has led to the suggestion that in making decisions the human operator accepts and organizes the available input information intermittently in the manner of a discontinuous servo. According to this view two nearly simultaneous stimuli can only be dealt with equally fast if they are grouped into a single decision to respond to both stimuli; otherwise one will have to wait for the attention of the central mechanism until the other has been dealt with. In the present experiment it is shown that delays in the second response are not necessary or invariable, and that the pattern and timing of the second responses when they are performed without delay differ in important respects from those to be expected of grouped responses. It is concluded that the central mechanisms concerned in the response do not possess the limitations that the single channel theory would suggest.