Abstract
Changes in performance at a visual vigilance task over eight 40-minute sessions were studied in three groups of eight subjects. The task was to inspect a series of displays of small disks for the occasional presence of a disk of slightly greater area than the others. For one group (search), each display consisted of a row of six disks. For one of the two no-search groups, the display contained two adjacent disks, one of which served as a reference standard; for the other group this reference disk was absent. Substantial improvement in overall detection rate occurred in all three groups. Analysis indicated that in each case this improvement was due to a genuine increase in discriminatory efficiency and not to any change in response criterion. Neither search nor the presence or absence of a reference standard appeared to affect the degree of improvement observed to any marked extent. Within-session decrement was observed only in the search group; this decrement was found to result from a change in response criterion, and not from any alteration either in discriminatory efficiency or search strategy.
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