My experiment is a bilateral tactile discrimination task measured with
the 275-channel CTF system. After a long struggle failing to localize
bilateral primary somatosensory sources using different beamforming
techniques, I have to say that I am now very happy with the results
SPM8's MSP returned. The sources are very similar to the fMRI results I
got from the same experimental design with the same group of subjects.
Many thanks to the program developers!
But now I have a problem with setting an optimal time window for group
inversion. My original trial length is 5.5s (-1.5 to 4s, -1s is visual
instruction onset, 0s to 0.6s is tactile stimulation, 1.6s is
instruction for button presses). My first approach was cutting the
trials [0 0.3]s and group inversion gave me very clear bilateral SI and
SII sources. I am just wondering whether I should feed the group
inversion a longer data piece as was suggested in the manual, e.g. to
include some baseline? As different brain sources are involved along the
trial, I am not sure how this will influence the results.
The second problem is, I couldn't run a 2nd-level t-test. I specified a
2x2 factorial design using the 8 mm smoothed images.
I defined the f contrasts as the following:
main effect: eye(4)
first factor: [1 1 -1 -1]
second factor: [1 -1 1 -1]
I had no problem running all the f tests but I run into errors when I
define the t contrast:
In spm_invTcdf at 93
In spm_u at 31
In spm_uc_RF at 30
In spm_uc at 39
In spm_getSPM at 705
In spm_results_ui at 277
??? Error using ==> betainc at 42
X must be in the interval [0,1]. etc...
I saw the same error reported in previous emails due to using unsmoothed
images. I thought that if I get some results from the f contrast testing
each factor, which is equivalent to a two-sided t-test, I should also be
able to get some results from a one-sided t-test?
Thank you very much for your help in advance!