LLN, le 3/03/05
Matthew, Daniel and the Others,
>Daniel wrote... I'm happy with just, "area X was significantly more
>active during task A than task B."
And so am I. In most of the case, that's what we are looking for and
what we should say. I don't see anything wrong (ok, let's forget
about the non-effect issue) if one adds something like "area Y was
not significantly more active during task A than task B".
The problem is, as Matthew correctly points out, that people (1) tend
to shorten the statement to "area X is activated by task A" and (2)
may go beyond the data concluding "area X differs from area Y for
task A". Concerning (1), authors should change their habits (make
their constrats really explicit and avoid incomplete statements) and
reviewers shouldn't accept fuzzy statements.
>To take the behavioral example... stating that they are impaired on
>spatial working memory is entirely uninteresting.
I totally agree if your assumption that people mean "particularly
impaired after multiple tests" is correct. They should clearly not
come to this conclusion if their patients failed lots of tests or if
they were only tested with 1 target task. Now, if your point is that
people test lost of tasks then, among those for which they find
significant differences, they report only what they want, it's no
longer a statistical issue...
>Obviously I'm drawing a parellel with the thresholded SPM map...
... which I'm not sure I agree with. In SPM maps, one usually DOES
test all areas for task A and B, and it is thus reasonnably
acceptable to says "area X was the only one significantly more active
during task A than task B".
Now, this may be a bit different with ROI analyses, and your example
makes me realize the risk when one only focuses on a priori areas and
forgets about the other activated ones claiming that they may be
false positive. That's another interesting issue...
>you can discuss trends in data.
I like trends when they are reported in the data section. The problem
is that many authors then "forget" to mention the trend in the
discussion/conclusion sections (I'm sure you've read tens of such
papers!) and, as many readers jump from the abstract to these
sections, weak conclusions spread in the scientific community. Is
this a valid reason not to use continous maps? I don't know, but at
least, we should be aware of this risk.
Yours,
Mauro.
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Mauro PESENTI
Research Associate, National Fund for Scientific Research (Belgium)
Unite de Neurosciences Cognitives
Departement de Psychologie
Universite Catholique de Louvain
Place Cardinal Mercier, 10
B-1348 Louvain-la-Neuve
tel.: +32 (0)10 47 88 22
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http://www.nesc.ucl.ac.be
http://www.nesc.ucl.ac.be/mp/pesentiHomepage.htm
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