MENTAL ROTATION AND THE RIGHT-HEMISPHERE

Mental rotation may be considered a prototypical example of a higher-o rder transformational process that is nonsymbolic and analog as oppose d to propositional. It is therefore a paradigm case for testing the vi ew that these properties are fundamentally right-hemispheric. Evidence from brain-imaging, unilateral brain lesions, commissurotomy, and vis ual-hemifield differences in normals is reviewed. Although there is so me support for a right-hemispheric bias, at least for the holistic rot ation of relatively simple shapes, it is unlikely that this bias appro aches the degree of left-hemispheric dominance for language-related sk ills. An evolutionary scenario is sketched in which the characteristic ally symbolic mode of the left hemisphere evolved relatively late and achieved the quality of recursive generativity only in the late stages of hominid evolution. This forced an increasingly right-hemispheric b ias onto analog processes like mental rotation. Such processes neverth eless remain important and are integral even to those processes we thi nk of as highly symbolic,such as language and mathematics. (C) 1997 Ac ademic Press.