Dear all,
In reaction to Eric Zarahn comments on the use of long blocks in
single subject analysis, I would certainly appreciate any other comments
on the validity of long blocks in fMRI design (2 -3 minutes blocks). We
are using movie parts (2.5 minutes with a TR = 4.0 sec) to trigger stong
emotional responses (in contrast to emotional images that are easier to
present in 30 sec blocks).
Our concern is should we try to ajust the emotional experience into 30
sec blocks ... or .... should we ajust the blocks lenght to the real
emotional experience? It is difficult to concieve that strong emotional
build up could simply be turned on and off at will.
Maybe a 1.5 tesla will introduce some noise but the use of a 3.0 tesla,
(that we are getting) that has a better ratio signal/noise could help.
And a good filtering procedure could reduce low frequency components.
With these adjustments, could long blocks be used safely? Are there any
other reasons why long blocks should be avoided?
Claude Breault
Research center
Institut Universitaire de gériatrie de Montréal
Montreal, Quebec, Canada
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