Hi Marco,
> I am also facing a similar problem, as I have tried to model time-locked
> events occurring within auditorily presented sentences (of more or less
> constant duration) in an event-related design with continuous fMRI sampling.
> Up to now, I have tried modelling the appearance of the verb with an informed
> set of hemodynamic basis functions (hrf + 2 derivatives) with very little
> success.
This is just an uninformed destructive opinion, but I would think that
the principal problem is that your excellent timing on the input side
(knowing exactly when which word appears) is somewhat destroyed on the
output side (the brain) by the smearing occurring by the real
hemodynamic response.
However, we have recently investigated the effect of removing certain
key words from a sentence and replacing them with a 750ms sinus tone
(Wilke et al, NeuroReport 2005). While there was a difference between a
simple block design analysis and an event-related analysis, it was not
huge, and our stimulus was certainly more discrete than a simple verb
within a sentence.
> I was now considering to use a FIR basis set time-locked to the beginning of
> each sentence, in order to try to capture responses associated to the
> processing of the entire sentence and/or to early or late sentence
> components.
I would think it's the brain that's the problem (not the basis
functions), but perhaps you can overcome some of the issues by
additional jittering.
> Does anybody have an idea of whether a FIR model would be appropriate for such
> a purpose? Would a Fourier basis set be better/worse?
No idea.
Best,
Marko
--
=====================================================================
Marko Wilke (Dr.med./M.D.)
[log in to unmask]
Universitäts-Kinderklinik University Children's Hospital
Abt. III (Neuropädiatrie) Dept. III (Pediatric neurology)
Hoppe-Seyler-Str. 1, D - 72076 Tübingen
Tel.: (+49) 07071 29-83416 Fax: (+49) 07071 29-5473
=====================================================================
|