If the `rest' periods between the task blocks do not contain any task at
all, then it is better to use a special regressor to model them.
IF the `rest' periods have a simple task, (ie for a visual task, looking
at a cross hair during the non-task blocks) then it is better to include
an extra regressor, to be able to separate task-specific visual activity
and general activity for using your eyes.
See also the reference to the `common mistake' to use a regressor for
rest in bjr.birjournals.org/cgi/reprint/77/suppl_2/S167
Saemann Philipp wrote:
> Hello all,
> we have a rather basic question on how breaks within an event-related fMRI
> paradigm (four types of "events") should best be handled.
> The final goal of the analysis is to contrast the four different types of
> events against each other.
> After block-like presentation of the four different, intermingled events,
> breaks of 20 seconds are programmed to allow
> the subject to rest. Should this "lower" baseline be explicitly modelled in
> a block like 5th regressor, or does this just
> introduce some collinearity that is not wanted?
> Thank you very much for any advice,