Hi, I have a question about how mkcontrast-sess works. I ran an analysis using the mkanalysis-sess option spmhrf 2 so there are three regressors for each predictor, the primary, the latency, and the dispersion. When specifying the contrast weights for mkcontrast-sess, the documentation indicates that they are specified in terms of the conditions as numbered in the paradigm file, not the individual regressors. Furthermore there only appears to be one contrast value output for each contrast, not three.
How are the three regressors being handled? I can think of several scenarios: 1) the contrast weights are not actually in terms of conditions (the documentation is incorrect), they are actually in terms of the regressors (so contrasting conditions 1 and 2 could be specified as -a 1 -a 2 -a 3 -c 4 -c 5 -c 6). 2) the latency and dispersion regressors are being ignored (a common practice). The contrast weights should therefore be specified as -a 1 -c 2. 3) The Calhoun et al (2004) approach is being used to combine the three regressors into a "derivative boost" amplitude measure. The contrast weights should therefore be specified as -a 1 -c 2. Thanks for any help you can give me! Joe -------------------------------------------------------------------------------- Joseph Dien, Senior Research Scientist University of Maryland E-mail: jdie...@mac.com Phone: 202-297-8117 http://joedien.com//
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