Search results

The effects of whole-body vibration at frequencies of 5, 7, and 11 c/s from 25–35 per cent of the human tolerance levels (defined by amplitude levels within each frequency) are to seriously reduce operator efficiency in performing tasks representative of those encountered in aerospace flight. Within the limits of the vibration conditions studied, the following conclusions were drawn from the research: (1) Decrements in vertical tracking performance ranged from 34 to 14 per cent. (2) Decrements in horizontal tracking performance ranged from 10 to 48 per cent. (3) The magnitude of the tracking performance decrements was related to the magnitude of integrated absolute Gz (output) measured at the sternum. (4) More procedural errors were committed under vibration than under static conditions.

The concept of measuring man's power output is not new, and indeed since about the turn of the century various devices have been used to measure the power man can generate when performing various tasks, such as cycling, hand-cranking, rowing, etc. Perhaps the task most thoroughly investigated is that of cycling, and from experiments, optimum cranking speeds and loads have been established corresponding to maximum power output over a given period of time. However, one important factor has been omitted in the majority of such studies. This factor is the effect of variation of muscle speed during the contraction period in each cycle. It is shown that this effect is marked and that under certain conditions power outputs greater than those currently attainable may be realised, the increase being of the order of 10–15 per cent. To achieve a desired speed-time relation, the motion of the muscle must be forced by external mechanical means, but this is readily accomplished without having to make use of an external power source.

Research was conducted to determine human operator abilities in a compensatory tracking task as a function of the precision of the displayed error information for various levels of task difficulty and practice. The controller dynamics were not varied and were such that displacements of the control were integrated twice before affecting the tracking error. Tracking error and the extent of control motion were the criterion measures. The results suggest that (a) increases in the precision of displayed error information result in a negatively accelerated reduction in the tracking error; (b) as the operator becomes more proficient, the relative superiority of an increased precision of displayed error is reduced; (c) the effects of the precision of information on control motion depends upon the difficulty of the task; and (d) the amount of control motion generally decreases as the operator becomes more proficient and the magnitude of this decrease is greater for an "easy" task than for a "difficult" task.

Man spends the greater portion of his life in sub-optimum states of consciousness. The paper reviews the experimental literature describing normal human performance at different levels of drowsiness and sleep, as these states are defined by electroencephalographic patterns. Among the types of behavioral responses to stimuli discussed are reflexes, simple movements, detection (i.e. arousal to external stimuli and awareness of internal states), discrimination, learning, and recall. Non-behavioral electroencephalographic responses are also described. Suggestions are made for future research.

A vigilance experiment was performed using a visual monitoring task with multiple stimulus sources. Under investigation were effects of repeated sessions on monitoring behavior. Nine 3-hour sessions were given on consecutive days. Following a longer 7-day interval, a 10th session was given. The main findings were a significant decrement in detection latency within each session, but no statistically reliable evidence for a between-sessions effect. Evidence was presented to suggest that the spatial configuration of stimulus sources was a factor for vigilance decrement because efficiency of the observing response decreased as a function of observation time.

Studies indicate that writers can overdo the personal approach in their copy, that reader-interest in subject matter can overrule readability. Mr. Ludwig will become assistant to the director of the School of Journalism, State University of Iowa, after receiving his master's degree there in June.