of what the right hemisphere "does." No one knows what it ... reasonable expectation that the results of focal cerebral brain damage can be interpreted as an ...
Marcel Kinsbourne Spatial thought and its representation in the brain have caught the public imagination. Alleged dichotomies in cognitive style have gained credibility based on the shift to the presumably "harder" level of analysis offered by hemispheric hypotheses. Rejecting the unitary notion of intelligence, on political as well as scientific grounds, some people consider intelligence as dual instead, with divergent or even contrary spirits housed in each half-‐brain. Such dichotomizing is unwarranted. Factor analysis as well as common sense tells us that intelligence is neither single nor dual but multiple and that no verified principle of brain organization characterizes the hemispheres as alternative packages of behavioral programs. Different cognitive styles exist and presumably rely on differently distributed use of brain processors; but, as De Renzi's scholarly and dispassionate analysis demonstrates, we are far from pinning down in useful detail the processes for which dominance is right sided, let alone from discerning among them some unifying thread. De Renzi pays scant attention to the multitude of rival formulations of what the right hemisphere "does." No one knows what it does. Studying the effect of local brain damage is a promising way to find out. Much of the current surge in interest in neuropsychology derives from the reasonable expectation that the results of focal cerebral brain damage can be interpreted as an uncoupling of anatomically distinct processors, some lost, others preserved. Thus conceived, neuropsychology is a route to establishing the factorial structure of higher mental functions. Also, classical neuropsychology can be used to determine the plausibility of hypotheses that purport to explain cognitive processing. If memory is legitimately divisible into episodic and semantic, context bound and context free, then differential damage should be capable of inactivating one system, sparing the other (it can). If "imagery" is explicable in terms of propositional coding, then mental representation cannot be impaired along analogue lines (it can, as demonstrated by Bisiach's studies of unilateral spatial neglect). Most of the time, however, De Renzi leaves it to others to extract the moral for cognitive science that is embedded in neuropsychological data. He deals with the data itself, critiques attempts to organize it, occasionally attempts a personal verdict, but essentially leaves matters as they are—unresolved. De Renzi's subject matter is in the main tradition of human experimental neuropsychology. Effects of brain damage are treated as opportunities to elucidate brain function. Procedures are designed to tap elementary cognitive processes that constitute the substructure of integrated behavior. The tests are as simple as possible, so that the function that limits performance in each can be inferred with some confidence. Given the need to delineate specific syndromes, sample size is necessarily small, and patients with diffuse damage are generally excluded from consideration. There is a brief historical introduction followed by eight chapters: two dealing with general issues of hemisphere specialization and six dealing with different categories of cognitive deficit. The first two, "The Development of Hemispheric Specialization" and "The Relation of Sex and Handedness to Specialization of Function," are competent reviews of topics that are frequently treated in the contemporary neuropsychological literature. The next chapter, "Disorders of Space Exploration,"
integrates important classical cases studies with relevant neuro-‐physiology group data. It considers the possible mechanisms of the phenomenon of unilateral neglect of space, a sequel of stroke that promises to hold the key to our understanding of how people distribute both their attention and their readiness to respond along the lateral dimension of space. Within the next chapter, "Spatial Perception and Deficit," is embedded a six-‐page critique of claims for formulations purporting to distill the unique contributions of both the left and the right hemispheres to cognition. De Renzi notes that the right hemisphere is most clearly characterized as dominant, not on tasks that tap the cognitive style, but on a variety of measures of direct perception, that are difficult to subsume under any one superordinate category. As a result he prefers the "admittedly crude characterization of the left brain as verbal and of the right as perceptual" (p. 192) to more ambitious formulations that do not well accommodate the existing evidence. In the next chapter, "Disorders of Personal Space Cognition," De Renzi concludes that though they are customarily treated separately, "disorders of spatial orientation and cognition occur also with respect to the body, but there is little evidence that they follow different rules than those governing comparable deficits in extrapersonal space" (pp. 206–207). He dismisses autotopognosia (inability to recognize one's own bodily parts) as an artifact, denying its specificity, and regarding it as an instance only of a general "defective recollection of how the parts of an articulated whole are spatially related to each other" (p. 202). His skepticism about the concept of disorders of body schema, whether general or localized, extends to finger agnosia (inability to recognize one's own fingers). De Renzi cannot account for this clinical phenomenon in terms of some more general processing disorder, so instead he weakens its effect by citing the discrepant criteria for its identification used by different investigators. Next comes "Disorders of Topographical Memory," on the first deficits in the "subdominant" hemisphere to be discussed in the English-‐language literature (by Paterson & Zangwill, 1944). Finally, constructional apraxia is considered. This impairment of ability to draw or copy simple figures and shapes has long been used by clinical neurologists as a bedside indicator of lateralized brain lesion. Experimental analysis has demonstrated that it may represent loss of either left-‐ or right-‐hemisphere contributions to the integrated performance, those contributions differing in nature. Here De Renzi characteristically inclines to the conservative position that performance on tasks of drawing and copying can be disrupted by right-‐hemisphere–based spatial disorder, as well as by apraxia based on left-‐ hemisphere disorder and by several other types of cortically based deficits. The book is an ample source of well-‐selected references. De Renzi has conducted his review of many different fields in neuropsychology with balance and good judgment, and he provides a solid basis for the further clarification of spatial disorders, and of right-‐hemisphere specialization in general. Reference • Paterson, A., & Zangwill, O. L. Disorders of visual space perception associated with lesions of the right hemisphere Brain, 1944, 67, 331–358.
