Abstract
Recent studies reported that manual performances with simultaneous speaking were less effective than those without it, especially on the right hand. Using a simple reaction time (RT) paradigm, we investigated the difference of the performances between the left and right hands with or without simultaneous vocalization and attempted to analyse the hemispheric differentiation of the efficiency on the vocal-manual simultaneous response.
The experiments were performed on 33 hemispheric patients due to CVD, 17 with the left hemispheric lesions (LHL) and 16 with the right (RHL), and 10 normal subjects. The subjects, responding to a peep sound 2-4 seconds after a warning signal, performd the following tasks: 1) single tasks; extension of the left middle finger, that of the right, or vocalization, and 2) simultaneous tasks; extension of the left middle finger or that of the right with vocalization. RTs of the finger extension and the vocalization were measured.
Compared to the controls the increase of RTs was significant in the affected hand of both the patient groups and in the vocal response of the RHL for the single tasks. RTs of the simultaneous tasks were not different between the controls and the LHL except the left hand, where-as those of the RHL were significantly larger than those of the controls.
The differences of RTs between the single and simultaneous tasks, Δ, were obtained by subtracting RT of a single task from that of a simultaneous task. Δ of the right hand increased more than that of the left in the controls and LHL. Compared to the controls, the RHL had significantly large Δ on the left hand and the vocal response combined with the left hand. Consequently the asymmetry of Δ between the left and right hands disappeared in the RHL.
Assuming that the vocal response is executed by both hemispheres with nearly equal potentiality, the differences shown in the patients with the left and right hemispheric lesions regarding the processing of simultaneous performances suggest the existence of a different central mechanism in each hemisphere. It is conceivable that the right hemisphere processes the simultaneous performances more effectively than the left hemisphere.
