In the present study we investigated whether the corpus callosum exerts an inhibitory or an integrative influence on hemispheric communication of magnitude information by
presenting prime–target pairs to the same or opposite hemispheres (intra- and interhemispheric number priming trials). During the experiment, subjects were asked to compare the targets with a fixed reference number and classify them as small or large. The prime stimulus was irrelevant for the task. To examine the interhemispheric communication of magnitude under present task conditions, we made use of a new presentation technique with filler items, thereby eliminating the latency benefit for intrahemispheric priming trials observed in previous studies. The results of this experiment showed equal priming effects for both intra- and interhemispheric priming conditions: stimuli were reacted to faster
when the numerical distance between prime and target was smaller (i.e. quantity priming) and when both prime and target required the same response (i.e. response priming). This is in line with the idea of a rapid integration of magnitude information between hemispheres.