Hello,
I have a question regarding experimental design if we are looking to
isolate delay activity during a memory encoding experiment. We would
like to have subjects encode a word (2.5s or so), followed by a variable
length fixation period (.5-8s). Our question of interest is whether a
given region of the brain which tends to have low (or even suppressed
compared to baseline) levels of activity during the stimulus encoding
phase may come on-line given enough time during the following fixation
period. We have a few questions about the best way to examine this
though as the encoding and fixation regressors would be correlated.
Assuming the stimulus presentation (encoding period) is of a set length,
the fixation onset is completely correlated with the stimulus onset. Is
there any good way to isolate this fixation activity? My impression was
that orthogonalising wrt to the stimulus regressor wouldn't be
sufficient to get around this problem.
Does the variable duration of the fixation phase help to disentangle
these two events or are the correlated onsets still the main issue? We
could vary the stimulus encoding duration independently, but this isn't
ideal behaviorally as it would be unclear whether the same processes are
occurring for the duration of the encoding event at longer times. Any
other ideas on how to approach this problem?
Thank you in advance for your help,
Jeremy
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