Lateralized dual-task performance: the effects of spatial and muscular repositioning

In three experiments subjects were required to perform different manual tapping tasks using either the left or right hand while concurrently performing a speech task. The major independent variables examined were muscular effort and the spatial and muscular repositioning components of the tapping tasks. In all speech conditions right hand performance was disrupted more than left hand performance. The degree of this lateralized disruption did not alter as a function of variation in either muscular effort or the repositioning requirements of the manual task. However, muscular repositioning activity, unlike other components of the motor task, was affected bilaterally by the addition of the speech task. Overall the results suggest that the dual-task procedure can be used to assess two types of "lateralized" interference effects; one relating to right hand performance, the other to left hemisphere performance.