Performance on direct and indirect tests of memory after mild closed head injury

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Abstract
Substantial anecdotal evidence suggests that mild closed head injury (C.H.I.) may result in memory impairment, but there has been little systematic research on this issue. The existing data do not provide a clear picture of whether memory is affected by mild C.H.I. primarily because of varying definitions of injury severity. In the present study, we defined mild C.H.I. using a set of objective criteria (i.e. Glasgow Coma Scale score, duration of loss of consciousness, and length of hospital stay) outlined by Rimel and her colleagues (Rimel, Giordani, Barth, Boll, & Jane, 1981). We then compared the memory performance of patients with mild C.H.I., matched control subjects, and college students, using both indirect and direct tests of memory. When tested indirectly, C.H.I. patients displayed normal memory for individual items and new associations. When tested directly, however, their memory performance was impaired. These results show that in the early weeks after mild C.H.I., memory is impaired and that the nature of this impairment resembles the memory disorder seen in individuals with mild chronic amnesia. In particular, mild C.H.I., like amnesia, seems to produce impaired memory performance only when test instructions require deliberate recollection of past events.