Expectancy and frequency effects on perceptual and motor systems in choice reaction time

Abstract

Three experiments investigated the effects of expectancy and stimulus frequency in character classification and identification tasks. Both expectancy and frequency were found to have effects on overall response latency, but the two factors had different patterns of interaction with two other experimental variables. The effect of visual quality was larger for low-frequency stimuli than for high-frequency stimuli, whereas the effect of quality was independent of expectancy. The effect of S-R compatibility was more strongly influenced by whether a stimulus was expected than by the frequency of the stimulus. The results suggest that expectancy and frequency have somewhat different effects on human information processing mechanisms. Expectancy allows temporary preparation for a specific S-R pair in response selection processes, but it has no effect on perceptual processes. Stimulus frequency, on the other hand, influences the efficiency of both perceptual and response selection processes. The overall effect of stimulus probability may be interpreted as having as components both expectancy and frequency effects.It has often been observed that people make faster and more accurate discriminative responses to stimuli that occur with relatively high probability than to stimuli that occur with relatively low probability (e.g., Fitts, Peterson, & Wolpe, 1963;Hyman, 1953;LaBerge & Tweedy, 1964). Phenomena of this kind, generally referred to as "stimulus probability effects," have been investigated extensively because of their importance for theories of reaction time (RT) in speeded choice tasks.This article addresses two questions emerging from the study of stimulus probability effects and attempts to show that they are related. The first question concerns the extent to which probability effects can be explained by the tendency to expect stimuli that are more probable: Does frequency of stimulus occurrence itself produce any effect, or does it only produce an indirect effect through the control of subjective expectancies? The second question concerns the locus of probability effects: What mental processes are influenced when probability is varied? Previous studies have examined these questions separately, and the present studies were designed to extend the results of the previous studies by looking at the two questions together.When a stimulus is presented with high probability,

The effects of stimulus sequence and probability on perceptual processing

“…Specifically, the effects of both probability and sequence should be greater at the low level of luminance. An additive relation between sequence and luminance would be evidence against the proposal of a sequential mechanism for the probability effect at encoding, and would thus be consistent with Miller and Anbar's (1981) proposal of a gradual practice mechanism for the effect. …”

“…These results suggest that the probability effect on perceptual processing is not an indirect result of sequential effects. Together with the results of Miller and Anbar (1981), they suggest that practice gradually acts to facilitate the perceptual processing of highly probable stimuli. …”

“…In other words, expectancy may underlie the probability effect at encoding, while some other mechanism is responsible for the effect at later processing stages. This possibility was tested by Miller and Anbar (1981), who varied probability, expectancy (by means of a pretrial cue), and luminance, permitting conclusions regarding perceptual encoding. They observed the usual interaction of probability with luminance, but noted no tendency for expectancy to interact with luminance.…”

Facilitation of Detectability and Criterion by Automatic Temporal Expectation

“…Del Fava and Ribeiro-do-Valle (2004) specifically tested this hypothesis and could not confirm it. Instead, their results indicated that temporal expectancy, defined as the attentional process generated by widespread networks of frontal, parietal and limbic areas (see Coull et al, 2000, andEngel et al, 2001) which produces a time dependent increase in the excitability of a specific sensorimotor circuit (Jennings, Van der Molen, & Steinhauer, 1998;Miller & Anbar, 1981; see, for a review, Sanders, 1966, Van der Heijden, 1992, and Nobre, Correa, & Coull, 2007, is most likely responsible for the effect. This process was named automatic (unintentional) temporal expectation by Nobre et al (2007), because it is automatically mobilized by the auditory prime stimulus.…”

Effects of visual and auditory stimuli in a choice reaction time task.

“…It occurs immediately after the WS and has a relatively short duration. Temporal expectancy is most commonly referred to as a process that induces a time-dependent increase in the excitability of a specific sensorimotor circuit (Jennings, Van der Molen, & Steinhauer, 1998;Miller, & Anbar, 1981;Sanders, 1966;Sullivan, Urakawa, & Cossey, 1996;Van der Heijden, 1992). It strongly depends on the relative probability of the occurrence of a relevant event at each moment.…”