Lateralized processing of centrally presented verbal and spatial tasks

Many of the investigators who have argued that each cerebral hemisphere is specialized for processing specific types of information have tested their hypotheses by lateralizing the presentation of stimuli to be processed. We conducted two experiments in which information that was assumed to be processed primarily by either the left or right hemisphere was presented centrally and tested for lateralized processing. In each of the experiments, subjects were given a dichotic listening task in which they were asked to identify the presence or absence of a target stimulus. They were instructed to attend to stimuli presented to one ear and to ignore stimuli presented to the other ear. Concurrently, subjects performed a centrally presented visual task: either a language task (Experiment 1) or a mental rotation task (Experiment 2). Performance on the language task was poorer for male subjects when they attended to the right ear than when they attended to the left ear. Female subjects were not affected by ear of attention. Conversely, performances on the mental rotation task were poorer when subjects attended to the left ear and when they used the left hand to perform spatial tasks. Although differences in strategies and task emphasis might account for the observed effects, we believe that differences in lateralization of processing were responsible