The Lateralization Of Arithmetic And Number Processing: A Review

Abstract

Calculation and number processing require ideographic and semantic operations which may involve the right as well as the left hemisphere. There is often also present a spatial component, whether overt as with column-addition or multiplication procedures, or covert if numbers are recoded into continuously varying analog quantities or magnitudes of a psychophysical or imaginal nature, to facilitate numerical comparison. Again right hemisphere mechanisms may be partly responsible. Evidence for such a minor hemisphere contribution is reviewed in the light of studies with clinical and commissurotomy cases, and normal subjects. Calculation itself is hard to define, as it often seems to reduce to the operation of overlearnt, associative, tabular look-up functions and algorithms. Indeed alphabetic comparisons analogous to numerical tasks should generate similar laterality effects in clinical and normal populations.