Laboratoire Psychologie de la Perception Institut Neurosciences Cognition Université Paris Descartes Centre National de Recherche Scientifique
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Comparison of perceptual and motor latencies via anticipatory and reactive responses

Distinct tasks have been designed to compare the timing of perceptual and motor decisions all of which have yielded systematic differences between these two ‘moments’. These observations have been taken as evidence of a sensorimotor dissociation. Inasmuch as the distinction between perceptual and motor decision moments is conceptually warranted, this conclusion remains debatable as the observed differences may reflect the dissimilarity between the stimulations/tasks used to assess them. Here we minimize such dissimilarities by comparing RT and Anticipatory RT (ART), an alternative technique to infer the relative perceptual decision moments. Observers pressed a key either in synchrony with the third of a sequence of three stimuli appearing at a constant pace (ART), or in response to the onset of this third stimulus presented at a random interval after the second (RT). Hence the two stimulation-sequences were virtually identical. Both the mean and the variance of RT are affected by stimulus intensity about 1.5 more than the mean and the variance of ART. Within the framework of two simple integration-to–bound models, these findings are compatible with perceptual and motor decisions operating on the same internal signal but being based on distinct criteria with the perceptual criterion below the motor one.