The Effects of Irrelevant Dimensions on the Predictive Value of a Warning Signal

Past research has neglected irrelevant dimensions of visual warning signals in choice reaction-time tasks. The present study examined the effects of an irrelevant dimension of a visual warning signal and that signal's value in predicting a response stimulus on choice reaction time. A warning signal, which was a geometric figure, appeared in the center of a VDT screen and was followed by one of two response stimuli (open circles). The predictive value of the warning signal was defined as the percentage of trials during which the warning signal accurately predicted the response stimulus by size and was manipulated in the present study as either .50, .66, .83 or 1.00. On half of the trials, an irrelevant dimension of the warning signal — its shape — was also varied. 24 male and 24 female subjects participated for 240 trials each. The results indicated that the fastest reaction times and lowest number of errors occurred when the predictive value was 1.00. However, there were no differences in reaction time between the conditions with predictive values of .50, .66, or .83. No errors were made when shape of the warning signal was varied (irrelevant dimension) than when it was not. These results support the hypothesis that predictive values of less than 1.00 as well as variations in an irrelevant dimension of a warning signal cause response competition in information processing, resulting in slower reaction times or increased number of errors.