The role of the left hemisphere in verbal and spatial reasoning tasks

Laterality of reasoning processes have long been a source of investigation. Differing formats of verbal and spatial reasoning tasks have meant it has not been possible to extricate true performance level from artefacts, of in put and output modalities. The Verbal and Spatial Reasoning Test (VESPAR) o ffers this opportunity, by virtue of matched sets of verbal and spatial ind uctive reasoning problems. Two series of 40 patients with unilateral left a nd right hemisphere lesions were tested on two verbal and two spatial subte sts of the VESPAR, together with a battery of baseline tests. The performan ce of the left and right hemisphere lesion cases was compared with a normal standardisation sample. Whereas only the left hemisphere group failed the verbal sections, both left and right hemisphere groups failed the spatial s ections. The influence of aphasia on spatial reasoning was considered to be an incomplete explanation for the failure of the left hemisphere group on the spatial sections. It is concluded that this investigation provides firm er evidence of a crucial role for the left hemisphere in both verbal and sp atial abstract reasoning processes.