Figure 2.

Hypothetical SAT functions. Illustrative SAT functions, plotted in d′ units ( of the standard normal deviate of the probability of correctly judging the target's orientation) versus processing time (time of the response cue plus observer's latency to respond) in seconds. (A) Expected pattern if cueing increases target discriminability only. The functions differ in asymptotic accuracy, but are associated with the same intercept (point when accuracy departs from chance) and proportional rate of information processing. (B) One expected pattern if cueing target location alters the rate of information processing only. The functions display disproportional dynamics; they reach a given proportion of their asymptotes at different times. Circles show hypothetical RT results plotted in SAT coordinates (abscissa = mean RT; ordinate = the accuracy level associated with mean RT), illustrating that RT differences can reflect differences in discriminability (A) or the speed of information processing (B). Approximately the same difference in mean RT and accuracy is consistent with either differences in SAT asymptote (A) or SAT dynamics (B). The position of the RT points on the corresponding SAT functions are determined by the decision criteria that an observer uses to balance speed and accuracy. Here, the hypothetical RT data are shown slightly higher than the 1 − 1/e (63%) point—a position often found in direct comparisons of RT and SAT procedures—illustrating that, in conventional RT tasks, observers often trade modest decrements in accuracy for substantial gains in speed (27–30).