The reliability of estimates of interhemispheric transmission times derived from unimanual and verbal response latencies.

In this study, the reliability of estimates of interhemispheric transmission times derived from verbal and unimanual responses was assessed. Responses were made to presentations of lateralized light flashes in a series of 20 experimental sessions, with responses being made to stimuli presented at three different retinal eccentricities. The reliability of estimates of interhemispheric transmission across 20 experimental sessions was generally poorer for verbal compared to unimanual responses. This was particularly true for stimuli presented close to the centre of the visual field. In addition, for unimanual response conditions, estimates of interhemispheric transmission times for the female subjects were longer in duration and exhibited poorer reliability than estimates found for the male subjects. In the verbal response conditions, there were no differences between the mean durations of the estimates found for the male and female subjects. The results suggest that for centrally located stimulus presentations, verbal responses do not produce reliable estimates of interhemispheric transmission time. This relatively poor reliability across experimental sessions may account for the mixed results seen in previous studies which have used verbal reaction times to estimate interhemispheric transmission time. The collection of unimanual responses to lateralized visual stimulus presentations is likely the best method of estimating interhemispheric transmission time in normal man.