Effect of Level of Activation on the Quality and Efficiency of Performance of Verbal and Motor Tasks

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Abstract
The primary purpose of the study was to test an implication of Duffy's two-dimensional hypothesis that all behavior varies along two independent continua, direction and intensity. If true, then whether tension level correlates positively or negatively with performance on a given task should be dependent on whether S directs his attention and effort primarily to that task, or whether he shares his attention with some other task situation or set of cues which interferes with performance on the task being measured. Secondary purposes of the study were to gain further information as to which muscles are the most reliable and sensitive indicators of activation level, and to observe the effects of continuous and distributed practice on performance quality, tension level, and performance efficiency. Sixteen Ss performed a rotary tracking (motor) task while simultaneously performing a nonsense-syllable memorization (verbal) task under four incentive conditions. Incentive was varied to manipulate the amount and direction of attention and effort directed to each task. The results provided strong evidence that the relationship between tension level and performance is dependent upon the direction in which S exerts his effort, as well as its intensity. Performance efficiency, expressed as the ratio of performance quality to tension level (EMG), varied with incentive, length of continuous work, and degree of skill. The EMG level of neck muscle was more sensitive to, and changed more consistently with, variations in incentive than did that of any of the other muscles from which recordings were obtained (frontalis, trapezius, and forearm flexors). Frontalis muscle was least sensitive to incentive variations. The results suggest that frontalis muscle tension level is not as good an index of activation level as is that of the neck or of several muscles combined. EMG gradients observed during continuous performance of verbal and motor tasks were interpreted as indicative of a progressive increase in activation level resulting from a change in the psychological significance of the task situation as perceived by S.

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