Am Montag, den 02.06.2008, 13:29 +0200 schrieb Markus Röhl:
> 1) I set up a model with only one condition – sound – that gets an
> 1st order parametric modulation – intensity. Further I include 6
> movement-regressors. The Stimulus duration is 5 seconds, the TR is
> 7.7. seconds (Block design). Despite the gap of 2.7 seconds where no
> stimuli is presented the entire regressor Sn(1) Stimulus*bf(1) (see
> attached Design Matrix.jpg) is continuously positive without any gap.
If it is indeed your TR that is 7.7 secs (i.e. the time it took to
acquire exactly one 3D image), then there is no gap in your regressor.
This is because in your observed time series there is only one value per
TR, and (at least in a block design) there is no way to infer any
changes in response that occured within one TR. Things would be a bit
different if TR and stimulus length were unequal (event related design).
Then, you would have a chance to observe hemodynamic responses at
different peri-stimulus time points. For a stimulus length of 5 and gap
of 2.7 seconds I'm not sure how well this would work, though.
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