Date of Award

7-1-1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Psychology

Abstract

Previous findings have suggested that glucose may enhance performance on memory tasks in rats and humans. However, other studies have shown that the effects of carbohydrates may vary by the time of their ingestion. The present investigation examined accuracy and latencies on a semantic task performed in the morning or evening and under two levels of blood glucose. The task consisted of three subtests. In the first subtest, subjects discerned the physical differences between word pairs. In the second subtest, they looked for word matches, regardless of typographical case. On the third subtest, subjects compared words for membership in the same or different semantic categories. Eighty-five male college-aged subjects were divided among the cells of a 2 x 2 factorial design, with Time of Day and blood glucose level as independent variables. Subjects were tested in the morning or evening, and ingested a solution sweetened with either glucose or saccharin. Results showed main effects for the type of solution and time of testing. Glucose ingestion and testing in the morning both increased the time required for decisions, but did not significantly affect the accuracy of responses. Further, blood glucose interacted with performance on levels of the Categorization Task, such that the most difficult task was unaffected by the level of blood glucose. There were no differences between subjects on an incidental test of free recall given at the conclusion of assessment. However, glucose and time of day interacted on a task assessing the strength with which subjects created cognitive prototypes of categories: subjects who received glucose in the morning demonstrated significantly slower responses than other groups. Results are discussed in comparison with previous human and animal studies demonstrating facilitative effects of glucose ingestion.

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