[Reaction time to dichotic visual stimulation and its relationship to cerebral hemispheric specialization]

There is a renewed interest in the study of the cerebral hemispheric specialization given its physiological, physiopathological, clinical and educational relevancy. According to this, a stimulus is better processed in one of the cerebral hemispheres. The visual dichotic stimulation allows to present a stimulus selectively to one of the hemispheres, and this was used in the present study for the measurement of the reaction time (TR) and for the establishment of its correlation with an objective and validated measure of the cerebral hemispheric specialization. Ninety eight persons with an average age of 22.2 +/- 0.7 (X +/- EE) years were studied by means of the Oldfield protocol for the determination of the Cerebral Hemispheric Lateralization Index (IL). Additionally, the age, the sex and the date of last menstruation in the case of females, were registered. The dichotic stimulation and the determination of the visual TR was accomplished by computer with a time resolution of 100 microseconds. The stimulus consisted of the random presentation of a white square on a black background in a computer monitor, to which the subject had to respond by pressing a key with his best hand. The reaction time was registered 10 times in each visual field for a total of 20 records per eye. The IL of the sample was predominantly right (66.32 +/- 4.64), and significantly smaller in males than in females (p < 0.05). The TR to stimuli in the left visual field was significantly greater (p < 0.05) than in the right visual field for both eyes. When analyzing the global results of each cerebral hemisphere, a TR significantly smaller for the left hemisphere (304.33 +/- 4.1 ms) than for the right (312.35 +/- 4.5 ms, p < 0.05) was observed. These results suggest that the cerebral hemispheric specialization, expressed as a smaller response time, cannot alone be only the product of a better intrinsic hemispheric processing of the information, but also of the anatomical relationships of the proximity of the hemisphere that receives the stimulus and the center or area that will generate the response, as is the case of the motor center located in the left hemisphere in the immense majority of the right-handed subjects in the sample and in the general population.