Hello SPM users,
I am interested in modeling Habituation within and between blocks of
stimuli similar to that conducted by Fletcher, Buchel et al (1999). I do
not have any behavioral measure such as learning so I have started with
simply a linear decrease of activation. I have conducted an analysis on a
single subject using parametric modulation and modeling the within
habituation linearly (ie 4 3 2 1) and the between habituation linearly as
well (ie 4444 3333 2222 1111). I have found some promising results though
some questions have arose:
1) Should I be convolving this model with hrf? If I am interested in
identifying voxels displaying linear habituation, than does using hrf bias
this result?
2) What are the parameters used when I select the time option for
parametric modulation? Is this simply a linear increase of activation
throughout the entire condition (within and between collapsed)?
3) When setting up contrast images, should I compare a parametric column
(1) to a baseline fixation column (-1) or is simply weighting the parametric
column as 1 (and everything else as 0) enough? When I do not explicitly
compare (ie weighting the parametric column as 1 with no comparison), what
does a significant voxel represent? Is it simply the extent to which this
voxel correlated with the parameters that I have entered?
Thank you very much, any advice is greatly appreciated ! Brian W. Haas
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