Neuropsychological assessment.

reasoning tasks. 7 The most posterior parts of both hemispheres are involved in early visual processing. Subcortical, as well as cortical, brain regions, are involved in attention and alertness. Subcortical brain regions are also involved in episodic memory, in some aspects of long term memory, and in the motor control of language. 12 A modularity approach to the analysis of cognitive skills implies that each complex cognitive process can be thought of as consisting of a series of functionally independent specialised subprocesses. 7229 The interaction of these subprocesses results in the complex cognitive skills. The way in which the cognitive processes are organised is often characterised, similarly to the "diagram maker" approach, in terms of flow diagrams that attempt to detail the way that the different subprocesses are brought together to perform a specific task. Empirical support for the modularity approach can be obtained at various levels including the neurophysiological, neuroanatomical, and neuropsychological. '031 For example, numeracy has been fractionated into several independent components: cognitive mechanisms for number comprehension, number production, arithmetical fact retrieval, and arithmetical procedures. '2 The idea that complex cognitive skills are carried out by distinct subprocesses combined with the idea that there are highly specialised areas in the brain, has led many cognitive neuropsychologists to assume that a cerebral lesion can damage only some subprocesses within complex cognitive skills. Indeed, cognitive neuropsychologists have succeeded in showing many dissociations between the subcomponents of cognitive skills that allow valid conclusions about the nature and functions of the impaired processing components to be drawn. Methods ofassessment of cognitive