VARIABLE CRITERION ANALYSIS OF BRIGHTNESS EFFECTS IN SIMPLE REACTION-TIME

Using light onset as the stimulus in simple reaction time (SRT), the effect of stimulus intensity was studied in both between- and within-Ss experimental designs, using 60 undergraduate females. There was a strong intensity effect in both conditions but no significant interaction between the effect of stimulus intensity and the type of design. This differs from previous results with auditory stimuli where such an interaction has been demonstrated. When the criterion parameters of variable criterion theory were evaluated directly, the only significant effect was greater criterion variability in the between-Ss condition. Theoretical functions describing the growth of sensory strength for each intensity had different starting points and were largely parallel, showing only late temporal divergence. This provides an explanation of the rarity, in the SRT literature, of interactions between visual intensity and criterion variables. Correlations illustrating the relations between RT measures and theoretical criterion parameters are presented. Absence of the predicted relation between intensity and RT variability is evidence against theories relating RT to impulse rate treated as a Poisson process. (13 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved). © 1979 American Psychological Association.