Academic journal article Perception and Psychophysics

Locus of the Intensity Effect in Simple Reaction Time Tasks

Academic journal article Perception and Psychophysics

Locus of the Intensity Effect in Simple Reaction Time Tasks

Article excerpt

Evidence is still inconclusive regarding the locus of the stimulus intensity effect on information processing in reaction tasks. Miller, Ulrich, and Rinkenauer (1999) addressed this question by assessing the intensity effect on stimulus- and response-locked lateralized readiness potentials (LRPs) as indices of the sensory and motor parts of reaction time (RT). In the case of visual stimuli, they observed that application of brighter stimuli resulted in a shortening of RT and stimulus-locked LRP (S-LRP), but not of response-locked LRP (R-LRP). The results for auditory stimuli, however, were unclear. In spite of a clear RT reduction due to increased loudness, neither S-LRP nor R-LRP onset was affected. A reason for this failure might have been a relatively small range of intensity variation and the type of task. To check for this possibility, we performed three experiments in which broader ranges of stimulus intensities and simple, rather than choice, response tasks were used. Although the intensity effect on the R-LRP was negligible, S-LRP followed RT changes, irrespective of stimulus modality. These findings support the conclusion that stimulus intensity exerts its effect before the start of motoric processes. Finally, S-LRP and R-LRP findings are discussed within a broader information-processing perspective to check the validity of the claim that S-LRP and R-LRP can, indeed, be considered as pure estimates of the duration of sensory and motor processes.

Reaction time (RT) is known to decrease as a function of stimulus intensity, approaching an asymptote for the most intense stimuli. This is particularly true for simple reactions, but not always for more complex tasks (see, e.g., van der Molen & Keuss, 1979). Stimulus intensity has usually been considered a factor influencing only very early stages of information processing. Evidence supporting this view has come both from studies employing the additive factors method (AFM) and from psychophysiological measures. It has been shown that the intensity effect on RT is additive with the effects of otiier factors, such as foreperiod duration, stimulus-response compatibility, number of alternatives, stimulus probability, and practice (e.g., Everett, Hochhaus, & Brown, 1985; Miller & Pachella, 1976; Niemi, 1979; Pachella & Miller, 1976; Raab, Fehrer, & Hershenson, 1961; Sanders & Andriessen, 1978; Schweickert, Dahn, & McGuigan, 1988; Shwartz, Pomerantz, & Egeth, 197). According to AFM, the additivity of intensity and other factors means that the stage affected by intensity is different from the stages affected by those other factors. Therefore, one might reasonably assume that this particular stage occurs very early in processing, distant from other stages. This claim has gained further support from electrophysiological studies in which the effect of intensity on simple RT and on the latency of early components of event-related potentials (ERPs) have been directly compared. Using this approach Vaughan, Costa, and Gulden (1966), Wilson and Lit (1981), and Jaslcowski, Pruszewicz, and Swidzinski (1990) found that visual intensity had identical effects on simple RT and on the latency of the N1 component These findings suggested that the processes later than those reflected by the N1 (which peaks at about 100-150 msec) are independent of stimulus intensity. Evidence from a number of other studies, however, is in conflict with this view.

For example, Miller and Pachella (1973) showed that stimulus intensity interacted with stimulus probability in a verbal-naming task and in a memory-scanning task with digits as stimuli. Nevertheless, these two factors were later shown to be additive in a same-different matching task (Pachella & Miller, 1976) and in a memory-scanning task with unfamiliar visual forms as stimuli (Miller & Pachella, 1976). However, another study by Stanovich and Pachella (1977) additionally revealed an interaction of stimulus-response compatibility and stimulus intensity, the latter finding being difficult to reconcile witii the claim that stimulus intensity exerts early effects only. …

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