Unilateral versus bilateral presentation methods in the reaction time paradigm

The use of bilateral presentation in lateralized tachistoscopic reaction time (RT) tasks has been precluded by problems of how to instruct the subject to respond to the left visual field (LVF) or right visual field (RVF) stimulus and by the necessity of fixation control with bilateral presentation. J. Schmuller and R. Goodman (1979, Brain and Language, 8, 81-91; 1980, Brain and Language, 11, 12-18) offered a method, applied to date only in recognition accuracy studies, which can overcome these problems. They used an "arrowhead pointer" at fixation. This instructs the subject as to which stimulus to report first and also controls fixation. We adapted the method to the RT paradigm by having subjects report only the stimulus indicated and applied it in a bilateral presentation version of the Object Naming Latency Task (W. F. McKeever & T. L. Jackson, 1979, Brain and Language, 7, 175-190). Fifty subjects received the unilateral task and 50 received the bilateral task. The bilateral task yielded right visual field superiority in 98% of the subjects and the magnitude of the superiority was over three times as large as in the unilateral task. Different sex x familial sinistrality x VHF interactions obtained on the tasks. Combining the advantages of reaction time and bilateral presentation methods may substantially increase the resolving power of lateralized tachistoscopic tasks.