On Wed, Dec 19, 2012 at 2:08 PM, Jens Kronschnabel
<[log in to unmask]> wrote:
> Dear SPMers,
>
> just two short questions on behavioral reaction time (RT) and BOLD signal
> which I hope are not too naive...
> 1) I have a significant group difference in RT. Are possible differences in
> hemodynamic responses between groups, that might be reflected in different
> RTs, in any way related to or even controlled for by including the temporal
> derivative at the first level?
The temporal/dispersion derivatives by definition doesn't change the
canonical HRF estimate since it is orthogonal. However, in practice,
you may get changes due to multiple conditions. You'd also want to
combine the derivative terms as has been done by Calhoun (2004) and
Steffener (2010)
> 2) Are possible differences in hemodynamic responses a matter not to worry
> about in block designs (in contrast to event-related designs)?
In a block design it is assumed that the neurons are in a steady state
across the entire block, so there should be no differences in the
duration of the response due to RT.
>
> Thank you very much for further insights.
> Best,
> Jens
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