To explain why speed increases in the demanded rate of work in a sensori-motor skill led to a disproportionate deterioration in performance, specific association was sought between signals omitted and definable temporal relationships occurring as a result of continuous display changes. The distribution of the time interval between the signals presented was such that some relationships occurred many more times than others, the frequency being determined by the mean signal speed. A detailed examination of performance in these terms revealed that omissions occurred close to the nearest response more often than would be expected by change, and they were as likely to occur just before the response as just after. Furthermore, the probability that a signal would be omitted when it occurred at a constant time interval from a response increased linearly with mean speed. Increasing the signal speed (1) increased the chances that a signal would occur close to a response, thus subjecting it to a hazardous temporal situation; (2) if a signal did occur close to a response, it increased the chances that it would be omitted. This latter effect was not due to the crowding in of other specific events as the speed increased, but to the general effect of a shortage of time in the situation as a whole.