On the nature of intersensory facilitation of reaction time

Abstract

Two experiments examined the RT to visual stimuli presented alone and when either auditory (Experiment 1) or kinesthetic (Experiment 2) stimuli followed the visual event by 50 or 65 msec, respectively. As has been found before, the RT to combined stimulus events was 20 to 40 msec shorter than to visual events alone. While such results have generally been interpreted to mean that two sensory modalities are interacting, Raab’s (1962) hypothesis of statistical facilitation— that the subject responds to that stimulus modality whose processing is completed first—is also possible. Using Raab’s model, but with relaxed assumptions, the present experiments show that RT to combined stimulus events is more rapid than can be accounted for by statistical facilitation. Therefore, some intersensory interaction was probably occurring. The nature of these possible interactions and the status of the statistical-facilitation hypothesis are discussed. Supported in part by Grant BNS 80–23125 from the National Science Foundation to the second author.