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The effects of time-of-day, task and effort on resource allocation


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Long, Gillian Elizabeth 2009 , 'The effects of time-of-day, task and effort on resource allocation', PhD thesis, University of Tasmania.

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Performance on a range of cognitive tasks is known to vary across the day. The
precise effects of time-of-day depend on individual differences, the nature of the task
and physiological factors. Several event-related potential (ERP) studies have found
significant time-of-day effects on ERP components, including a reduction in P3
amplitude in the afternoon/evening compared to the morning (Higuchi, Liu, Yuasa,
Maeda, & Motohashi, 2000; Wesensten, Badia, & Harsh, 1990) and increased P2
amplitude in the afternoon compared to morning (Wesensten & Badia, 1992). In
contrast, other studies have reported minimal (or no) time-of-day effects (Broughton,
Aguirre, & Dunham, 1988). Geisler and Polich (1990) suggest ERPs are only
indirectly affected by time-of-day, with factors which vary across the day, such as
food intake and body temperature, having more direct effects. With the exception of
Higuchi et al., all published ERP investigations of time-of-day have used single-task
paradigms, which may be less sensitive to time-of-day effects than dual-task
paradigms. In addition, no reported studies to date have investigated effects oftimeof-
day on P3a. The primary aim of the current series of seven experiments was to
determine the impact of time-of-day on ERPs during a series of dual-task experiments
and to determine if a dual-task paradigm would be more sensitive to time-of-day
effects than a single-task paradigm. As voluntary levels of effort invested in task
performance have been reported to increase during periods of low arousal (Hockey,
1997), it is possible fluctuations in effort mask effects of time-of-day on resource
availability. Therefore, an additional aim of this series of experiments was to determine whether voluntary effort invested in tasks varies across the day and if so,
the impact of this on ERP components.

During Experiment 1, 12 participants completed a visual oddball braking task
and a concurrent visual tracking task with varying priority, at 0900 and 1300. When
priority was given to the oddball task the effect of time-of-day was significant, with
amplitudes of P2 and P3b greater at 0900 than at 1300. Fourteen participants
completed a single oddball braking task and easy and difficult dual-tasks (braking and
tracking) during Experiment 2. P2, N2 and P3b amplitude were greater during the
single-task than both dual-tasks and there was no evidence of P3a during any of the
task conditions. Modification of the braking task stimuli during Experiment 3 resulted
in significantly greater P3a amplitude during the single-task compared to the dual tasks
and lower P2 and P3b amplitude during the dual difficult task than the dual easy
task. During Experiment 4, 16 participants completed single, dual easy and dual
difficult tasks at 0900, 1300 and 1700. The effects of time-of-day on P3b were not
significant during the single-task however during the dual-tasks significant time-of-day
effects occurred with larger P3b amplitude at 1700 than at 1300. At 1300 P3a was
consistent across the tasks, whereas at 0900 and 1700, P3a amplitude was greater
during the single-task than the dual-tasks. Experiment 5 aimed to determine if effort
modulated ERP effects. Sixteen participants completed easy and hard versions of a
cued visual RT task, at 0900, 1300 or 1700, in which they were instructed to used
standard or 'extra' effort. Contingent negative variation (CNV) was significantly
greater following effort cues than standard cues; however the effects of time-of-day
were not significant following either cue type indicating effort was consistent across
the day. During Experiments 6 and 7, 16 participants completed the tasks used in
Experiments 4 and 5, in caffeine and placebo conditions, to determine whether previous significant findings were consistent with effects of increased arousal
associated with caffeine. The results of Experiment 6 revealed a trend towards greater
P3b amplitude in the caffeine condition than the placebo condition. During
Experiment 7 the effect of caffeine on CNV was not significant suggesting levels of
voluntary effort were consistent across both conditions.
Overall, the results indicated time-of-day has significant effects on several
ERP components including P2, P3a and P3b; however it appears the effects on P2 and
P3b are only evident during tasks which are sufficiently difficult to require total
capacity of attentional resources. Dual-tasks appear to be more sensitive to time-of-day
effects than single-tasks, with dual-tasks that engage the same supply of
attentional resources being more sensitive than those tasks which place demands on
wider resources. Although subjective effort varied across the day, changes in arousal
due to time-of-day and caffeine did not significantly affect levels of effort invested in
task performance, as measured by CNV amplitude. Together, the findings suggest
time-of-day variations in arousal affect ERP measures of resource allocation, but not
effort, during tasks which place high demands on resources.

Item Type: Thesis - PhD
Authors/Creators:Long, Gillian Elizabeth
Copyright Holders: The Author
Copyright Information:

Copyright 2009 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
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Available for use in the Library and copying in accordance with the Copyright Act 1968, as amended. Thesis (PhD)--University of Tasmania, 2009. Includes bibliographical references

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