RT to tactile stimuli presented ipsi- and contralaterally to the responding hand

Subjects had to react with the hand which received a tactile stimulus (uncrossed condition) or with the hand opposite to the hand which received the stimulus (crossed condition). Four experiments were conducted. In the first three, subjects knew which hand would receive the stimulus and which hand would have to respond. In the first two experiments, subjects reacted to a simple tactile stimulus while in the third subjects had to perform a tactile discrimination before responding. No significant differences in RT under the crossed and uncrossed conditions were observed in the first three experiments. In the fourth experiment, subjects did not know which hand would receive the stimulus, and they also did not know which hand would have to respond. Under these conditions, large significant differences in RT between the crossed and uncrossed condition emerged.

The study includes a criticism of a simple structural interpretation of interhemispheric transmission time (IHTT) as proposed by Bashore (1981). Support is provided for the view that in paradigms of the kind used here, allocation of attention to a psychologically defined hemispace is a more important factor in observed RT than structural links between stimulus and response mechanisms.