Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)




The present study examined the effects of time of day on short-term memory efficiency in older and younger adults. Forty-five young (18-35 years of age) and thirty-six older (over 60 years of age) adults were selected for participation. Subjects were tested individually at 0900 hrs, 1400 hrs or 2000 hrs. Two measures of memory scanning and three measures of memory span were employed. Memory scan measures required subjects to scan working memory for sets of 2, 3 or 4 digits or words. Memory span measures included digit span, word span, and sentence span. The digit and word span measures were the largest list of digits or words the subject could repeat without error. The sentence span measure required the subject to read sentences aloud and remember the last word in each sentence. Sentence span was considered the largest set of "last words" the subject was able to repeat in order.

Results revealed no effect of time of day or age on slopes for word scanning. Analysis of the digit scanning task revealed that slopes decreased across time of day, indicating that subjects scanned working memory faster when tested at 2000 hrs than at either 1400 hrs or 0900 hrs. Results of the memory span analysis revealed no effects on digit span. However, younger adults had larger word spans and sentence spans than older adults. The present results replicate previous work indicating that the rate of memory scanning for digits improves across time of day (Anderson et al., 1988). No effects were observed when words were used as stimulus materials. The absence of any age differences in memory scanning is inconsistent with previous research (Salthouse & Somberg, 1982) suggesting that a larger number of subjects should be tested to examine this result further. The age differences in memory span observed in the present study are consistent with Light and Anderson (1985) suggesting that working memory processes are less efficient in older adults. The lack of any interaction between age and time of day suggests that circadian variations do not differentially affect younger and older adults.

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