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Abstract:
Abstract: Most neuroimaging research requires participants to
perform various tasks, which vary depending on the particular topic
of interest (working memory, attention, etc). These tasks typically
involve presenting stimuli to participants and measuring their
responses. Yet, the precise neural mechanisms underlying the
processes required to encode a stimulus and select a response
remain unknown. A better understanding of these processes would aid
in the interpretation of data across a variety of experimental
situations. This study investigates these processes by manipulating
factors (i.e., stimulus contrast and stimulus-response
compatibility) believed to differentially affect the duration of
these processing stages. Participants performed a well-practiced
choice-reaction task during fMRI scanning under two difficulty
levels for each factor. Our behavioral results confirm the
independent effects of these factors and suggest that stimulus
contrast affected the duration of stimulus encoding and
stimulus-response compatibility affected the duration of response
selection. Our neuroimaging results suggest that increased stimulus
encoding difficulty is associated with increased activity mostly in
right prefrontal, premotor, and parietal cortices; whereas
increased response selection difficulty is associated with
increased activity mostly in left prefrontal, premotor, and
bilateral parietal cortices. Little activation was found for the
interaction of these two factors. These data are consistent with
previous research and are among the first to show independent
additive effects of factors in both behavioral and neuroimaging
data.
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