Abstract: Many supervisory tasks such as piloting aircraft and operating auto-mated factors as well as daily living pose requirements to remember ran-domly occuring stimuli (S) calling for specified responses (R) at specifiedtime, where S-R intervals overlap in complex ways. In this experiment,this S-R situation is simulated. Simple messages were presented on thescreen of IBM PC/XT randomly and briefly to specify alphanumeric keyswhich had to be pressed at an indicated time. The results of the experi-ment are as follows: (Ⅰ) intervallic time for the stimulus presentationinfluences the performances of overlap memory which will increase withthe increasing of the intervallic time and explain the fraction of time busyis one of the time factors of the mental workload.

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