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Dear Bill, > I am analysing an experiment as a single condition where all trials > (epochs) each correspond to a different parameter value. In SPM the timing > of each of the 180 trials is specified by a vector of onsets values (using > a previously loaded matlab variable). For some reason when later prompted > by SPM to enter the parameter values corresponding to the onset vectors the > parameter vector length expected by SPM is only 179, rather than 180, which > is incorrect since the vector lengths for the onsets and the parameters > should be the same. At some point, SPM99 generates stick functions from the onsets (around line 279 in spm_get_ons.m). Note that the stick functions are not in continuous time, but discretized into time bins. It could be that two of your onsets are so close together in time so that they fall into one bin and only one stick function is generated for two events. If this is the case, you could increase the number of bins per TR (have a look at spm defaults, statistics fmri) to disambiguate between the two events. The other solution is to remove one of the events that are too close together from your onset vector. Stefan -- Stefan Kiebel Functional Imaging Laboratory Wellcome Dept. of Cognitive Neurology 12 Queen Square WC1N 3BG London, UK Tel.: +44-(0)20-7833-7478 FAX : -7813-1420 email: [log in to unmask]