Dear SPM users,
i designed a 2back paradigm with face-stimuli. Therefore, each stimulus
is presented for 2 seconds to make sure that subjects are able to
comprise the whole stimulus. Overall 30 face stimuli are presented which
leads to a 70 seconds block length (including inter stimulus time). The
control condition is a 0back paradigm with same block length. Based on
the desired limited hit ratio of 12% i am not able to shorten the block
length.
Computing the model in a standard blocked design with high pass filter
at 128 seconds leads to a very strange looking design matrix where the
two conditions are not really differentiated from each other (optically
at least). I tried to compute the model with 256HPF but this leads to a
very strong and unspecific signal over the whole brain. I know that this
overall block length is too long for SPM modelling but i am wondering if
there is a possibility to analyse this paradigm anyway with SPM. Maybe
someone has got experience with the analysis of such designs.
i am really looking forward to hear from you
kind regards
christian
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