The Relation of an Environmental Variable to Performance in a Prolonged Visual Task

Abstract

In a previous paper (Fraser, 1950) on the relation between angle of display and performance in a prolonged visual task (Mackworth's Clock Test), it was suggested that the presence or absence of the experimenter might affect performance on vigilance tasks. In Mackworth's original experiments (Mackworth, 1950) the subject was in a closed cabinet by himself, and as far as possible all external noise and stimuli were excluded. In the angle of display experiment, the writer sat in the same room as the subject, out of his sight, and there was no particular attempt to exclude the ordinary external noises, etc. It seemed worth while to follow up the previous experiment with another to test the hypothesis that the presence or absence of the experimenter might influence performance in such a task. A new apparatus was devised for this purpose, which possesses some advantages over the Clock Test.