Sequencing in frontal lobe patients.

Abstract

An experimental neuropsychological study was undertaken to investigate whether frontal damage selectively affects the ability to carry out sequencing tasks. Thirteen patients, assigned to an Anterior Group on the basis of locus of brain lesion, were compared to nine patients assigned to a Posterior Group. Each of these groups was compared to a Normal Control Group, matched for age, sex and level of education, on two sequencing tasks. In the first, Increasing Span Task, subjects were required to organize sequences of increasing length. Verbal and pictorial subtests, consisting of four, six, nine and twelve unit sequences, were presented separately. The second, Capture Error Task, was designed to assess sequencing performance on tasks where a potential for capture errors exists. A capture error, in this study, was defined as the incorrect successive pairing of two items which tend to be frequently and routinely associated with one another but which, in the context of the present task, should be separated and used in a less characteristic way. The potential for a capture error was created by presenting a series of six unit sequences in which a special association existed between two successive units; this association was sometimes valid (i.e., the units should remain together in the final solution) and sometimes invalid (i.e., the units should be taken apart and used separately in the final solution). Twenty verbal sequences and twelve pictorial sequences were administered separately in two subtests. The results on the Increasing Span Task showed that while neither Anterior nor Posterior groups had difficulty organizing short (4 unit) sequences, subjects in the Anterior group were particularly sensitive to sequencing tasks at normal span and beyond. The results of the Capture Error Task showed that the Anterior group differed from their Control group and from the Posterior group in their ability to arrange sequences correctly when a potential for capture errors was present. The theoretical implications of these results for the role of the frontal lobes in behavior are discussed.