EFFECTS OF EXPECTANCY AND ATTENTION IN VIBROTACTILE CHOICE REACTION-TIME TASKS

The orienting of attention in space has not been considered in the tactile domain. This issue is examined using a modified version of a visual paradigm initially adopted by Posner, Snyder, and Davidson (1980), which manipulates the probability of a stimulus occurring at different spatial locations. Slower RTs at an unexpected stimulus location are thought to reflect the time required to shift attention from the expected to the unexpected location. In two experiments involving vibrotactile choice RT between left and right hands, the two hands were either crossed or uncrossed, and the hands were held both on the left side of the body, both on the right, or one on either side of the midline. There was no evidence to suggest that spatial location (left or right) affected the orienting of attention in the tactual modality. As predicted, RTs were slower when the arms were crossed compared with uncrossed, though this effect was smaller for the expected trials. A coding conflict hypothesis may explain both these findings, but the smaller effect in the expected trials may also reflect attentional factors. Both the relative and absolute location of the hands affected the magnitude of the cross-arm effect and indicated that attention may play a role in the perceptual division of space into left and right sides. Possible reasons for hand or hemispace asymmetries in different simple and choice RT paradigms were discussed.