I. THE PROBLEMSMost tasks do not consist of reactions to single stimuli spaced at intervals of a few seconds; ordinarily, for example, when dealing with a control mechanism (as in tracking a moving target) the human being has to attempt to follow a continuous series of stimuli, or a continuously changing stimulus. Two main questions then arise:(1) Does the operator respond continuously or intermittently?(2) If he responds intermittently, how long is the psychological refractory period, i.e. how long must elapse after the presentation of one stimulus before a response can be initiated to the next stimulus in the series? Telford (1931) has already pointed out that in a rapid series of stimuli the ordinary reaction time to auditory signals can be increased by 0.1 sec. by reducing the time interval between stimuli from 1.0 to 0.5 sec. PRELIMINARY EXPERIMENTS : CORRECTIVE PERIODS IN TRACKING RECORDS(1) Procedure Experiment Z. In Fig. 1 A is reproduced a typical record obtained when the subject is required to wind a balanced handwheel at a constant speed. The aim of the subject was to maintain a pointer steady on a straight circumferential white line drawn on a rotating smoked drum. The pointer was actuated by a motor, so that it moved steadily away from the line, and required a compensatory movement of the handwheel at a rate of 1 r.p.m. to keep it on the line.Experiment ZZ. In Fig. 1, B, C and D show records made in carrying out similar tasks; but in these cases the pointer was actuated by a cam (three different cam courses were used and are shown in the record in each case), which caused the recording pointer to move according to a predetermined course. The subject could compensate for the pointer movements by moving a handle up or down, and his task was to keep the pointer on a horizontal white line previously drawn on the smoked drum.Experiment ZZZ. Using the apparatus of Experiment 11, and the cam course illustrated in Fig. 1 B, eight subjects were given the same task, a t five different drum speeds: 4,10, 20, 50 and 100 mm./sec.

No abstract

No abstract

No abstract