Research investigated the utility of an alternative technique for the study of vigilance performance. The usual approach has been to study how well subjects responded to a signal of given difficulty; this technique altered the difficulty of the task to ensure a fixed level of performance. A computer-based, self-adjusting program presented background stimuli--a pair of dots 4.25 inches apart displayed on a cathode ray tube--and special stimuli--a pair of dots with wider spacing. The amount by which the latter width exceeded 4.25 inches was raised if subjects failed to discriminate it and lowered as they succeeded, to maintain a fixed discrimination rate. Results indicated that the adaptive variable behaved in a manner consistent with the usual measures of vigilance decrement--i.e., that vigilance dropped sharply at first and then levelled off. Thus, increased widths for the special stimuli were required over time. It was concluded that this technique could be used as a research tool in vigilance studies and that it has practical applications for the training of human monitors of equipment in military, industrial, health and computer fields. (Author/PB)