Abstract
Does the brain have common representations of external space across different sensory modalities? This question was examined by Spence and his colleagues who reported the crossmodal congruency effects (CCE); subject's speeded elevation discrimination responses on tactile stimuli were much better when both tactile and light stimuli were presented in congruent elevation in hands rather than in incongruent elevation. We tested whether the CCE were the artifacts caused by the type of response. In the typical crossmodal congruency task, the target tactile stimuli that subjects had to discriminate were presented to fingers while subjects had to respond via foot pedals. The different body parts involved in tactile stimulus reception and discrimination response might have affected the response difficulty asymmetrically for the congruent and the incongruent conditions. We examined this possibility by comparing the CCE measured with two types of responses; finger response and foot response. The experimental equipments were specially designed in order to allow subjects to respond via the fingers receiving the tactile stimuli. The experimental stimuli were quite similar to those used in the typical crossmodal congruency task. The distance between left and right hands was manipulated in three levels (i.e., 7 cm, 13 cm, and 25 cm) while the distance between an index finger and a thumb was fixed at 13 cm. The typical CCE were found when measured with foot response. When measured with finger response, however, the CCE were found only when the visual distracters were presented to the same hand side with respect to the tactile targets. The effects of response type on CCE were consistently obtained over the three levels of hand distance. This result suggests that the CCE depends on response type and its implication should be revisited.
Supported by M103KV010021-04K2201-02140 from BRC, 21st Century Frontier Research Program