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According to a recent hypothesis, executive functions should be particularly vulnerable to the effects of total sleep deprivation. Random generation is a task that taps executive functions. In three experiments we examined the effects of total sleep deprivation on random generation of keypresses, numbers, and nouns, in particular on the suppression of prepotent responses and the selection of next responses by way of applying a local-representativeness heuristic. With random key-presses suppression of prepotent responses did not suffer from lack of sleep, but it became poorer at a sufficiently high pacing rate. In contrast, suppression of prepotent responses suffered when numbers and nouns were generated. According to these findings different types of random generation tasks involve different types of inhibitory process. With only four response alternatives, but not with larger response sets, application of the local-representativeness heuristic was impaired after a night without sleep. In terms of a simple formal model, serial order representations of the preceding responses are used in selecting the next response only for the small response set, and not for larger response sets. Thus, serial-order representations are likely to suffer from loss of sleep. These findings strongly suggest that random generation involves multiple processes and that total sleep deprivation does not impair all sorts of executive functions, but only some.

The ability of an optimum duration of inter-task system response times (SRT) to aid users in achieving a perfect readiness for task execution is systematically investigated. Three SRT duration conditions, namely, short, medium and long, were applied in a balanced repeated measures design. Medium SRTs are observed to enable the attainment of optimum readiness for task execution.

The physiological effects of motor activity during typical computer tasks are negligible. Such motor activity affects physiological measures only at a very high typing speed. The physiological effects of computer work are dependent exclusively on mental load at lower levels of motor activity. Skin conductance responses are the most sensitive indicators of the effects of mental load during computer tasks, which appears to be independant of physical demands.