Dear all,
I am currently wondering about the logic behind the VOI extraction for DCM
- or probably any type of connectivity analysis. The standard approach
seems to be that people use some straightforward contrast, i.e. attention
vs. no attention in the classic attention to motion dataset, to identify
target areas in the group analyses. The same contrast is then used to
identify local maxima in each individual subject and use these maxima as
the centre coordinate for VOI extraction. However, it seems to me that
this approach ignores interindividual variability: what if an area A is
driven by some bottom-up signal from area B, but the degree of this effect
varies across individuals? This could lead to a situation in which the
categorical comparison is unable to identify a local maximum for area A in
each and every subject (well, you might guess it - I am currently dealing
with such a dataset). Do people then use alternative contrasts to search
for local maxima or are these subjects simply being excluded? And if the
latter, wouldn't we lose potentially interesting information regarding
interindividual variability?
Best,
Thomas
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Dr. rer. nat. Thomas Wolbers
Department of Psychology
University of California
Santa Barbara, CA 93106-9660
U.S.A.
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email: [log in to unmask]
www.psych.ucsb.edu/~wolbers
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