Which stages of processing are speeded by a warning signal?

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Abstract

This article reviews psychophysiological and behavioral studies that attempt to identify which stages of processing are speeded by a neutral warning signal (WS), that is to say, one that conveys no information about the nature of the imperative stimulus or the required response. Experiments involving the lateralized readiness potential (LRP) provide evidence against the widely held view that warning effects on reaction time (RT) are due to facilitation of low-level motor processes. Studies of modality-specific evoked potentials similarly rule out a locus within sensory–perceptual processing. It is concluded that the speeding of RT by a neutral WS is most likely due to nonspecific motor priming within an early phase of response selection. In addition, fast-guess responses, in which subjects choose a response without fully analyzing the stimulus, are assumed to contribute to warning effects.

Introduction

The effect of a neutral warning signal (WS) on reaction time (RT) is one of the oldest and most thoroughly investigated phenomena in the history of psychology. Among the goals of early research was to determine which of the processes that intervene between stimulus and response are influenced by the subject's preparatory state. In the first published work on this topic, the founding father of experimental psychology theorized that a WS allows attentional preparation. This preparation, in turn, facilitates both sensory and motor processes during the reaction interval (Wundt, 1881, cited in James, 1890 vol. 1, p. 429).

Little progress was made during the ensuing half century or so. Localizing an effect to some point between stimulus and response was not a problem that could be easily subsumed within the Behaviorists’ agenda. Nonetheless, a number of important empirical relationships were documented during this era, including the effect of foreperiod duration on RT (Woodrow, 1914, cited in Woodworth, 1938, and discussed below).

Section snippets

The additive factors method

The advent of the Additive factors method (AFM; Sternberg, 1969) in the early days of the cognitive revolution brought renewed interest in determining which stages of processing are speeded by a WS. Using this approach, the experimenter factorially manipulates a variable of interest in combination with one or more additional factors that have a known locus of effect. In studies of warning effects, the most common variable of interest was temporal uncertainty. AFM studies of this variable

Fast-guess responses

Later in this review, we will present evidence against Sanders’ assumption that WSs facilitate late motoric processes. Our evidence is based mainly on a movement-related brain potential, the lateralized readiness potential (LRP). However, there is another aspect of Sanders’ theory that LRP data have generally supported. Before describing this concept of fast-guess responses, we will explain what the LRP is and how it is extracted from the signal-averaged event-related potential (ERP) recorded

Other event-related potentials

Surface electrophysiological measures, such as the LRP and other ERPs, have proven superior to the AFM for identifying and studying stages of information processing. Psychophysiologists who use such methods have made important contributions toward identifying the locus of warning effects, especially in the case of WSs that serve as precues. The term precue indicates that the WS conveys information either about the nature of the impending stimulus or response. Using ERPs, psychophysiologists

Reflexive reactions and voluntary response force

Other psychophysiological methods that have been used to study warning effects include somatic reflexes and analog measures of voluntary response force. To understand the relation of these findings to RT it is important to consider a distinction drawn in the cognitive literature between effects at long or intermediate foreperiods versus very short ones. Properly speaking, only prestimuli delivered at onset asynchronies greater than 500 ms are to be considered WSs. When shorter asynchronies are

Lateralized readiness potential and visual evoked potential studies

The reader will take comfort in learning that the studies to be reviewed in the present section are in complete agreement with one another. The first five involve using the LRP as a temporal landmark to distinguish early versus late effects during the reaction interval. The logic here is the same as that described above for P3 latency. In the case of the LRP, though, there is no controversy among experts in the field regarding where in the brain the component comes from, the general nature of

The model

Our model to account for the just reviewed LRP and VEP data is shown in Fig. 5. We assume that a WS speeds processes subsequent to the sensory–perceptual analyses indexed by modality-specific evoked potentials. Accessory stimuli have not been tested in this regard, but there are enough parallels with warning effects to assume that the locus of action is the same. This locus must be prior to onset of the response-specific motor processes reflected by the LRP. Based on these electrophysiological

Acknowledgements

We thank Rolf Ulrich, Jeff Miller, Gabriele Gratton, and Nelson Cowan for helpful discussions. The preparation of this paper and our previous research on this topic was supported by grants from the Spanish Ministry of Culture, Education, and Sports and the autonomous government of Galicia.

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