Can callosal speed of transmission be inferred from verbal reaction times?

Filbey and Gazzaniga (1969) found that verbal reaction times were shorter to right than to left visual field stimuli. They interpreted this reaction time difference (30 to 40 msec) to reflect callosal transmission time, i.e., the delay required for information received in the right hemisphere to be acted upon by the verbal left hemisphere. We have performed four verbal reaction time experiments with normal subjects, utilizing differing hemifield stimulus presentations and task requirements. Stimuli were: small lights (light-emitting diodes); checkerboard pattern briefly flashed; small circles; consonant-vowel-consonant triads, either meaningful or nonsense. Contrary to Filbey and Gazzaniga's observations, we found no difference between verbal reaction times to left and right half-field presentations, or a significantly shorter reaction time with left-field presentations, depending upon experimental conditions. Faster reaction times with left-field stimuli were found in left-handed as well as right-handed subjects. Our data indicate that it may be premature to infer callosal speed of transmission from verbal reaction times to half-field stimuli. The paradoxical finding of faster verbal reactions to right hemisphere visual inputs does not appear to be related to handedness, and it occurs with meaningful stimuli; this finding remains unexplained.