A study of electromyographic changes associated with mental work

Abstract

Earlier research has shown that certain fluctuations are characteristic of mental work curves. Other investigations have revealed changes in muscular tension during mental work. The aim of the present experiment was to follow simultaneously these changes in output and in tension throughout a simple mental task. As the variations were likely to be rapid, recordings were made over short intervals of time˙ Two methods were employed to modify and thereby illuminate the relationship discovered between the two variables: (1) Muscular tension was induced during work. (2) An attempt was made to change the mental set of the subjects towards the work. Ten female subjects took part in the experiment and worked at addition sums under the three conditions: 1˙ N type when addition was performed at an easy steady speed which could be kept up for ten minutes. 2. P type when addition was performed as above while a spring balance was pulled at half maximum effort. 3 M type when subjects worked at maximum speed. The addition sums were of three lengths, 6, 11, and 21 figures per sum, and subjects added three sums of each length under each condition (27 sums in all). In order to prevent a possible slowing down due to the progressive increase in -ii-the size of the addend, addition in pairs was employed. Subjects added aloud and each verbalization was recorded on a tape and a later check made for errors. Electrodes were placed on the chin and the dorsal surface of the right forearm and leads taken to an electromyograph which recorded by "pen" on Teledeltos paper. The chin electrodes gave an indication of the moment of speaking and the arm electrodes a measure of tension in the forearm. It was thus possible to correlate the speed of work, indicated by the distance between clusters of spikes on the chin record, and the level of muscular tension, indicated by the mean height of the waveform from the forearm during the period between the verbalizations. In this way variations in output and tension could be followed during the course of work. It was found that a high negative correlation occurred between speed and tension under all three conditions. Starting and end spurts occurred over short time intervals in all sums in both time and tension curves. The longer sums led to slower work and tended to lead to more tension. These results can be interpreted to support the hypothesis that tension facilitates work of this kind, a suggestion which is reinforced by the results from the induced tension conditions. Subjects worked more quickly under P conditions and became more tense under M conditions. Large individual differences were noted but not examined in detail. The ways in which tension may facilitate mental processes and the relevance of this work to the peripheral theory of thought are briefly discussed.