HM REVISITED - RELATIONS BETWEEN LANGUAGE COMPREHENSION, MEMORY, AND THE HIPPOCAMPAL SYSTEM

Three studies tested the claim that H.M. exhibits a ''pure memory defi cit'' that has left his ability to comprehend language unimpaired rela tive to memory-normal controls. In Study 1, H.M. and memory-normal con trols of comparable intelligence, education, and age indicated whether sentences were ambiguous or unambiguous, and H.M. detected ambiguitie s significantly less often than controls. In Study 2, participants ide ntified the two meanings of visually presented sentences that they kne w were ambiguous, and relative to controls, H.M. rarely discovered the ambiguities without help and had difficulty understanding the first m eanings, experimenter requests, and his own output. Study 3 replicated these results and showed that they were not due to brain damage per s e or to cohort effects: Unlike H.M., a patient with bilateral frontal lobe damage detected the ambiguities as readily as young and same-coho rt older controls. These results bear on two general classes of theori es in use within a wide range of neurosciences and cognitive sciences: The data favor ''distributed-memory theories'' that ascribe H.M.'s de ficit to semantic-level binding processes that are inherent to both la nguage comprehension and memory, over ''stages-of-processing theories, '' where H.M.'s defective storage processes have no effect on language comprehension.