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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