ABSTRACT
A common theme of all contributors to this book is that, because tests of executive function have low test-retest reliability and uncertain validity, it has been hard to draw clear empirical distinctions between “executive” and “nonexecutive” tasks. It has also proved difficult to relate particular behaviours which have become regarded as being paradigmatic exemplars of “executive” function to specific neuroanatomical areas or neurophysiological systems. We argue that some of these difficulties occur because executive behaviour has been discussed, simultaneously, at more than one level of description. Accounts of purposeful and conscious behaviour, in the language of everyday subjective experience, map uneasily onto clinical taxonomies of the modes of dysexecutive function observed in brain-damaged patients. Performance indices empirically measured in laboratory tasks are often treated as being directly equivalent to the hypothetical system performance characteristics specified in functional models of working memory and selective attention. As a result, it has passed unrecognised that hypothetical components of “executive behaviour,” such as “inhibition,” “planning,” “monitoring” and “control” which are, in fact, simply descriptions of task demands, may have very poor construct validity because although these demands appear logically different they can be met by identical production system architectures. Confusions have also arisen because both task performance indices and system performance characteristics have been treated as equivalent to statistical constructs, derived to explain individual differ ences in performance on intelligence tests, such as Spearman’s (1927) index gf (see review by Rabbitt, 1996).
