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

[Cecile Issard]

Hello Luca,

What are the 40 s you average? Only one block? Or a block + silence? It seems to me that 50 to 80 ms is very short in between blocks.

Best,

Cécile Issard
PhD student
Laboratoire Psychologie de la Perception
Université Paris Descartes- CNRS
Paris, France

Le 11 mars 2017 5:06 PM, Luca Filippin <luca.filippin at gmail.com> a écrit :
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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