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Dear Guillaume, Thank you very much for your detailed reply! My educated guess was also something similar; however, I could not find any indication of testing onset units in the code... On the other hand, I can understand that it would not change much in the model. 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] -----Original Message----- From: Guillaume Flandin [mailto:[log in to unmask]] Sent: Tuesday, March 10, 2015 11:55 AM To: Tibor Auer Cc: [log in to unmask] Subject: Re: [SPM] Time modulation 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