Evaluation of Mental Strain by Palm Sweating during Short-term Memory Task

Abstract

This paper reports on the investigation of palm sweating during short-term memory tasks and testing the availability of the amount of palm sweating for an index evaluating mental strain. Six male subjects performed sets of thirty tasks with digit strings ranging from 4 to 9 digits at random order. The correctness of recalled answer, subjective difficulty for mental stress and palm sweating at each task were recorded. The amount of palm sweating (PS) was measured using hygrometry with a ventilated capsule attached on the left palm. Correct answer rates suddenly decreased over 7 digits. Subjective difficulty tended to increase with an increase in string-length. PS tended to decrease exponentially with the repetition of tasks at each string-length, and the exponential regression curve was fitted between PS and order in tasks at each string-length. Estimated PSs were obtained at 1st, 15th and 30th tasks from the regression curves. Estimated PS at 1st task tended to increase in proportion to string-length. Each estimated PS at both 15th and 30th tasks had a threshold for increasing. Also, estimated PS increased in proportion to the string-length at no less than the threshold. The thresholds were 5 digits at 15th and 6 digits at 30th task. These present findings suggest that PS is an index available for measuring mental strain. Also, this index describes the level quantitatively in adaptation for mental stress.