Focal hemisphere and visuoperceptual categorization 1

In the past 20 years extensive research on visuoperceptual disorders after focal brain damage has shown that injury to the right cerebral hemisphere is especially detrimental to performance on several tasks involving processing of visual stimuli. Individual findings, however, have so far proved to be scarcely susceptible of a unitary interpretation. Isolated explanatory essays relating interhemispheric asymmetries in perception to stimulus characteristics, either physical (Meier and French, 1965; De Renzi and Spinnler, 1966; Milner, 1967) or semantic (Kimura, 1963; Milner, 1967; De Renzi et al., 1969), or to different strategy along the analyticholistic dimension of visual processing (LevyAgresti and Sperry, 1968; Nebes, 1971; Levy et al., 1972) are not exempt from criticism and/or cannot cope with the whole body of empirical findings. Bisiach and Faglioni's (1974) data have indeed challenged the view according to which right brain-damaged are more impaired than left brain-damaged patients in visual processing of complex patterns. On the other hand, an investigation by Basso et al. (1974) on the susceptibility of unilateral brain-damaged patients to the Mueller-Lyer illusion failed to confirm the