Dear Tibor,
if the onsets are specified in scans, this creates a time parametric
modulator in units of minutes - a change was made from seconds to
minutes units many years ago to avoid very large values that could occur
with long time series and polynomial expansion.
Now I assume that you are referring to the fact that if onsets are
specified in units of seconds, the multiplication by TR is superfluous
and should be removed - I'll change the code accordingly.
Note that it doesn't affect the model itself but only the scaling of the
regressor and still corresponds to a linear time effect.
Best regards,
Guillaume.
On 09/03/15 17:15, Tibor Auer wrote:
> Dear SPMers,
>
>
>
> I have noticed a strange thing in SPM (SPM12 r6225) “converting” time
> modulation to parametric modulation:
>
> In spm_run_fmri_spec.m, lines 231-7:
>
> / /
>
> /%-Time Modulation/
>
> /if cond.tmod > 0/
>
> / P(1).name = 'time';/
>
> / P(1).P = U(j).ons * job.timing.RT / 60;/
>
> / P(1).h = cond.tmod;/
>
> / q1 = 1;/
>
> /end/
>
>
>
> Why are the onsets multiplied with TR and divided by 60?
>
>
>
> Vale,
>
>
>
> Auer, Tibor M.D. Ph.D.
>
> MRC Cognition and Brain Sciences Unit
> 15 Chaucer Road
> Cambridge
> CB2 7EF
>
> United Kingdom
>
> Phone/Work: +44-(0)1223-273613
>
> Mail: [log in to unmask] <mailto:[log in to unmask]>
>
>
>
--
Guillaume Flandin, PhD
Wellcome Trust Centre for Neuroimaging
University College London
12 Queen Square
London WC1N 3BG
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