> * The given sot.mat file in the web had 4 column and one row at
> first. then each column has 26 rows( N1& N2 for non-familiar
> and F1 & F2 -for familiar faces). Since it has 26 faces for each
> group that's why sot.mat matrix had 26 rows and for N1,N2,F1& F2
> , it had 4 column.
>
Correct
>
>
> * sot.mat file contain the stimulus onset times, i.e.- it contain
> the information when the stimuli has been given. As the
> information provided in the web, after showing one face for 0.5
> sec it gives a interval of 4 sec. After that it showed another
> face for 0.5 sec. *so obviously the time interval between the
> two consecutive showing face is at least 5 sec*. But when i load
> the sot. mat file in the matlab and open the sot cell, i found
> that there are some *time interval between the consecutive
> stimuli is 2.25 sec.* I am attaching the screen-print. Please
> check the attach file.
>
Because the stimulus onset times are in units of scans, TRs, not
seconds. This should be stated in the manual.
>
>
> Question : 1) Why the time interval is 2.25 sec?
>
See above
> Question : 2) The picture is shown for 0.5 sec then in analysis time
> why we put duration (0) ? [ref: SPM5 manual.page 213( on
> the step of Modeling categorical responses)
>
Won't make much difference to stats. Suggest you read some more
papers/course notes from the SPM website.
> Question : 3) In case of the following experiment what should be the
> stimuli time difference? Is the answer [12 24 36 48…..] and the
> duration [1]? Please verify my answer.
>
If you specify the onsets in seconds, rather than scans (in the GUI),
then yes. Whether you enter duration 0 or 1 will make little difference
(assuming all durations constant), because of the convolution with the HRF..
>
> Experiment : Subjects were instructed to perform a key-press with both
> index fingers every time they saw the word tap appear on the screen.
> The stimulus appeared every 12 sec and remained on the screen for 1
> sec. In the interim, subjects were instructed to fixate on a white
> cross-hair in the middle of the screen. There were 24 trials in a
> 5-min block.
> question 4) what should be number of rows and columns (according to
> the experiment state above) in the sot.mat file?
> question 5) From where i could learn more about content of the sot.mat
> file?
>
If you are beginning with SPM, I suggest you use the GUI, and enter your
onsets by hand, or from a text file.
Rik
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MRC Cognition & Brain Sciences Unit
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