Interhemispheric transmission of information in manual and verbal reaction-time tasks

In principle, interhemispheric transmission time can be assessed in normal man by measuring simple reaction time (RT) to lateralized light stimuli. Two paradigms have usually been employed: (1) a manual RT paradigm, whereby interhemispheric transfer time is equated with the difference between ipsilateral and contralateral responses, and (2) a vocal RT paradigm whereby interhemispheric transmission time is equated with a right field/left hemisphere advantage. Experiment I demonstrated the expected systematic advantage of the ipsilateral over the contralateral manual responses, but failed to show a right field advantage for four types of verbal responses, including two monosyllabic and two bisyllabic words. The RT of a blowing response was also equal for the two visual fields. In Experiment II the same words that had failed to yield a right field advantage in Experiment I were used for discriminating between digits presented in the right and left visual fields. Digits were discriminated by naming or by association with a given word. In both tasks RT was significantly faster for right field presentations, and the advantage over the left field was about 5 ms. In Experiment III verbal and manual RTs were measured in a task involving the discrimination between single and double light stimuli presented in the right and left visual fields. There was a nonsignificant advantage for the right field, which was equal for manual and verbal responses. It is concluded that the right field superiority observed with verbal stimuli is due to the processing of the input, and is independent of the verbal or non-verbal nature of the output.(ABSTRACT TRUNCATED AT 250 WORDS)