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Abstract:
Cognitive performance and physiological variables appear to
vary across a 24-hour period. Prior research has demonstrated that
immediate, short-term memory performance tends to be better in the
morning, while longer term recall is more proficient in the
afternoon. Cognitive demands of certain tasks appear to affect
regional cerebral blood flow (rCBF), which can be indirectly
measured by tympanic membrane (TM) thermometry. TM temperature also
appears to vary as a function of time of day. This study was
designed to determine how time of day affects task performance, how
TM is affected by the time of day, how rCBF (as measured by TM
temperature) changes as a result of task performance, and how these
three variables interact. Participants were tested at two different
times of day on two tasks, a short-term memory task for words and a
visuo-spatial matching task for numbers. TM temperature was
measured while participants were performing each task in order to
determine how rCBF fluctuates as a function of task demands.
Results indicated that there was a significant time of day effect
on task performance, with both tasks showing increased performance
in the evening. Temperature analyses demonstrated that there was a
time of day effect on TM temperature, and TM temperature changed
significantly during tasks, depending on the type of task being
performed. Implications of results for theory and research will be
discussed.
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