[Cognitive tasks and simple reaction times: new observations].

Simple reaction times to lateralized unstructured visual stimuli were studied in normal subjects while they were carrying out a concomitant task. In one task strings of four digits, randomly chosen from 1 to 9, were acoustically presented to the subjects who had to repeat them at the end of each presentation, in a second task again strings of four digits were presented and the subjects were asked to pay attention to the stimuli without memorizing them. In order to compel the subjects to listen carefully to the stimuli, in the second experiment, intermixed with the digits, a letter was occasionally presented and the subjects had to repeat it. It was found that the memory task facilitates reaction times mediated by the left hemisphere, whereas no hemispheric differences were found in the purely attentional task.