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

[Luca Filippin]

Hi Cecile,
   the 40s average (plus -2 seconds for the baseline) includes the ~18 or
~22 seconds stimlus plus 22 or 18 seconds of silence, leaving off ~10s of
more silence before the next stimulus onset. And each stimulus is made like
I described before

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

I used the word 'block' which is probably misleading to indicate, within
the same stimulus, the train of N or M 'BI' interleaved.
20-80 ms is the silence (within a stimulus) between a train of N and a
train of M BI-sound.

I hope this explain better.

Thanks for any suggestion.
Luca


On Sun, Mar 12, 2017 at 5:10 PM, Cecile Issard <
cecile.issard at etu.parisdescartes.fr> wrote:

> 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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