I don't think it'd be possible unless in your design you sometimes have
one event but not the other, and other times have both events together.
See e.g. Ollinger et al. (2001) Neuroimage. Is the "sustained" response
actually sustained throughout the experiment?
Regarding your other question, intuitively I would guess that the
response to the transient event would *not* be the canonical HRF;
perhaps you should check out some papers on adaptation though? Perhaps
in primary auditory cortex you wouldn't see a canonical response, but
maybe somewhere like Wernicke's area would show different behavior
(assuming the sustained noise wouldn't "activate" that area).
Michel Hoen wrote:
> Dear SPM experts,
>
> I'm analysing data from a study where subjects have to listen to one word presented in background noise.
>
> I was trying to model two types of events, the raw presentation of the noise (one "sustained" event lasting 3.5 s) and the presentation of the word embedded inside that noise (one "short" event lasting 1s).
>
> Yes I am looking for this needle in that haystack.
>
> If I model the short event only, will the correct form of the BOLD response be the HRF, and anyway what will it reflect lots of hay and a bit of needle ?
>
> In other words, if you first stimulate sensory areas with a sustained stimulation and add on top of that a transient event, will the BOLD response to that transient event still be the canonical HRF ??
>
> I'm asking that because actually we have very nice responses on the time-derivative but not on the canonical HRF and I was wondering if eventually the special combination of stimuli: 1 sustained + 1 transient on top (or deeply hidden in it actually ....) would modify the form of the bold response to the transient stimulation to something different than can_HRF.
>
> Any remarks, thoughts, references, I guess this should be the same for any type of paradigms using 1 sustained + 1 transient stimulation in the same modality.
>
> Thanks very much in advance,
>
> Michel Hoen
>
>
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