[Homer-users] Odd HRF shape: possible explanations?

[Luca Filippin]

Hi,
   we've been using Homer2 to analyze some data collected on newborns and
we get some puzzling HRF shapes as result, averaged over a 40 secs temporal
window The function has in some cases multiple humps: it rises then
descends a bit and then rises again, descends again and so on, 2 or more
times. In some other cases it simply rises and doesn't fall at all.

Would you have any explanations for that?

We believe that it has something to do with the stimuli design.

Our stimuli are sounds of variable length between 18 and 22 secs, roughly.
Each sound is made of block of N repeated short sound segments (for
example: BI), interleaved with other blocks of M sound segments of the same
type BI, but shorter duration:

N x BI (pause) M x shorter BI  (variable pause) N x BI (variable pause) M x
shorter BI  (variable pause) ...

where "variable pause" is a silent segment of duration between 50 and 80 ms.

We wonder if  there's a way to do the analysis so to disentagle the
contribution of each block of sound segment within a sound stimulus. We
play different sounds during the experiments: each sounds onset is
separated by roughly 50 seconds. The problem would be perhaps, the
estimation of the baseline.

Many thanks for your help,
Luca
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