Blinking during Visual Tracking

In order to determine the incidence of blinks during visual tracking, their effect, and the nature of this effect, two experimental arrangements were used. In one the subject had to keep a pen upon a moving line, his blinks being recorded without his knowledge both electronically and by two observers. In the second he had to keep two pointers in line using a positional control, the display being occluded intermittently in one part by a wheel tachistoscope, in another by his own voluntary blinks. It was found that the blink rate was raised when the subject expected the tracking to start, and again after tracking. During tracking it was reduced, particularly initially. The lowest blink rates were recorded during or immediately before the difficult periods of the course. It was not possible to predict the blink rate while tracking from a knowledge of the true “resting” blink rate. Although blinks were Infrequent when the course was difficult, it was here that they caused the largest errors, especially when anticipation was not possible. This effect was due partly to interference with vision, but only temporary inattention could account for the delayed deterioration following blinking. It has been suggested that the blink rate might serve as an index of attention, blinking being one of the earliest signs of inattention.