Date of Award


Degree Name

Master of Arts



First Advisor

Dr. Jack L. Michael

Second Advisor

Dr. Alyce M. Dickinson

Third Advisor

Dr. R. Wayne Fuqua

Access Setting

Masters Thesis-Campus Only


Previous research has reported a direct relation between performance accuracy on a signal-detection task and the probability of critical signal occurrence. However, most of this research has involved relatively brief sessions, and no studies have investigated this effect for more than one experimental session. The purpose of the current study was to investigate the effects of a high (. 18) and a low (.02) probability of critical signal occurrence across multiple sessions, with each session lasting two hours.

In the current study, four undergraduate students, ranging in age from 18 to 21 years viewed a computer screen showing two simulated gauges. Each gauge was comprised of 20 equal segments that darkened randomly (for about 1 sec.). A critical signal consisted in the simultaneous darkening of two adjacent segments. When this occurred, subjects were required to press the spacebar on the computer keyboard. Critical signals were presented at a probability of either .02 (the "A condition); or .18 (the "B" condition). Two of the subjects were exposed to the "A" condition. The other two subjects were exposed to the values of the independent variable in a B-A-B order.

Two of the four subjects showed almost no performance inaccuracy under any of the conditions, and the other two showed considerable variability unrelated to the different conditions. The results of this experiment can thus not be considered either to confirm or to refute the results of earlier studies demonstrating the signal probability effect.