The critical role of group studies in neuropsychology: comprehension regularities in Broca’s aphasia

We reexamine the empirical record of the comprehension abilities of Broca’s aphasic patients. We establish clear, commonly accepted, selection criteria and ob-tain a pool of results. We then subject these results to a detailed statistical analysis and show that these patients comprehend certain canonical sentences (actives, sub-ject relatives, and clefts with agentive predicates) at above-chance levels, whereas comprehension of sentences that contain deviations from canonicity (passives, ob-ject-gap relatives, and clefts) is distinct and is at chance. That the latter is the case, and patients indeed guess at such structures, we show by comparing the distribution of individual results in passive comprehension to that of a model for such guess-ing—an analogous series of tosses of an unbiased coin. The two distributions are virtually identical. We conclude that the group’s performance is stable, and well-delineated, despite intersubject variation whose source is now identified. This means that certain comprehension tests may not always be used for the diagnosis of individ-ual patients, but they do characterize the group. It also means that group studies The preparation of this paper was made possible by NIH Grants 00081 and DC 02984 t