glm.singlestudy_tmap
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— | glm.singlestudy_tmap [2010/08/24 13:39] (current) – created jochen | ||
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+ | ====== GLM:: | ||
+ | ===== Motivation ===== | ||
+ | After running the regression for a single study (run, i.e. one FMR, VTC, or MTC object), creating t-contrast maps for just this study can be beneficial in determining whether or not a certain run contains too much noise (or specific artefacts) for it to be included in second-level statistics. Also, it is sometimes desired to use the actually standard-error-normalized effect-statistic (t instead of regression beta) for further computations (e.g. to incorporate a measure of within-subject-data noise on the second level). | ||
+ | |||
+ | ===== Requirements ===== | ||
+ | You need to have a GLM file/object available that represents the regression outcome of a single run. **Please note that, at this time, the support for FMR (MAP creation) has not been implemented; | ||
+ | |||
+ | ===== Method reference (' | ||
+ | < | ||
+ | |||
+ | FORMAT: | ||
+ | |||
+ | Input fields: | ||
+ | |||
+ | c NxC contrast vector (default: full model and main eff) | ||
+ | mapopts | ||
+ | | ||
+ | | ||
+ | |||
+ | Output fields: | ||
+ | |||
+ | map | ||
+ | |||
+ | ===== Reference notes ===== | ||
+ | **The '' | ||
+ | |||
+ | ===== Usage example ===== | ||
+ | Say you have a study with 5 regressors of interest and 1 confound (mean study level, automatically added by BrainVoyager QX/ | ||
+ | |||
+ | * instruction | ||
+ | * motion in left visual field | ||
+ | * motion in right visual field | ||
+ | * motion in both visual fields (at the same time) | ||
+ | * static (trials without any motion) | ||
+ | |||
+ | then the syntax to create a contrast over all conditions sharing motion in any visual field would be coded as: | ||
+ | |||
+ | <code matlab glm_singlestudy_tmap_ex1.m> | ||
+ | glm = xff(' | ||
+ | |||
+ | % create the contrast | ||
+ | contrast = glm.SingleStudy_tMap([0; | ||
+ | |||
+ | % name the contrast | ||
+ | contrast.Map.Name = ' | ||
+ | |||
+ | % save the contrast | ||
+ | contrast.SaveAs; | ||
+ | |||
+ | % clean up | ||
+ | contrast.ClearObject; | ||
+ | glm.ClearObject;</ | ||
+ | |||
+ | ===== Usage notes ===== | ||
+ | Please note the following details about this method and the example: | ||
+ | |||
+ | * at this time, the name of the contrast(s) cannot be specified but has to be set after the call | ||
+ | * multiple contrasts can be given whereas the number of contrasts is the number of columns in the weights argument | ||
+ | * each contrast should either have its weights be all positive (or all negative, weighted contrast over baseline, or reversed) or sum up to 0 (weighted differential contrast between conditions); |
glm.singlestudy_tmap.txt · Last modified: 2010/08/24 13:39 by jochen