Brain slow potential and ERP changes associated with operator load in a visual tracking task

Brain electrophysiological changes occuring during the course of a visual tracking task were recorded from 24 normal subjects under varying conditions of workload. Recordings were made with directly coupled amplifiers from 4 scalp midline locations and of vertical and horizontal EOG. The task was to track with a joystick a moving letter on a video monitor screen. Various decisions and button pressing responses were required from the subject during the course of each tracking trial, the total duration of a trial being 28 sec. Trial difficulty was varied by requiring identification of ‘targets’ or §non-targets’ based on a pre-learned 1-, 3- or 6-letter set of possible targets, by varying speed and distance travelled by the letter and by the introduction of movement perturbation. Sustained negative slow potential (SP) shifts were associated with the introduction and course of each trial. These had 2 phases: an early phase related to memorization and rehearsal and a later stage associated with the tracking itself. Increasing tracking difficulty resulted in an increased negative DC shift during the tracking stage. Increased memory set size caused a reduction in the negative shift during the preparatory, memorization phase. The experimental manipulations of difficulty also resulted in a number of changes in the amplitude and/or latency of ERP components associated with the various points of decision or response.