British Journal of Psychology

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Volume 60 Issue 2 (May 1969), Pages 149-285

SIGNAL PROBABILITY AND VIGILANCE: A REAPPRAISAL OF THE ‘SIGNAL‐RATE’ EFFECT (pages 169-178)

Performance on a 40 min. visual task was studied as a function of signal probability. A separate group was tested at each of five levels of signal probability (0·02, 0·06, 0·18, 0·24 and 0·36). Percent detections increased with signal probability. This increase was accompanied by a rise in the false report rate, and analysis in terms of signal detection theory suggested that signal probability affects the subject's criterion (β) rather than his ability to discriminate (d′).

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