contrasts

Contrasts are very similar to T-Tests, except that they allow the testing of multiple means with a set of user defined coefficients. In EMEGS, contrasts are always within contrasts, therefore the subject order in the batchfile must be consistent across all conditions. If you choose 'Contrasts from list', you are given a set of predefined coefficients, of which you can choose. Otherwise, you have to enter the coefficients yourself. In either case, the order of your coefficients must correspond the condition order in your batchfile and their total must equal zero. Moreover, you can choose to use a normal distribution for the testing, or to use a distribution, generated by ..... (permutation test).

For instance, consider a contrast to compare 3 groups of visual evoked potentials: those evoked by pleasant pictures, those evoked by unpleasant ones and those evoked by neutral ones. And suppose your hypothesis would be that over visual areas, the potential for emotional pictures is more negative than that of neutral pictures. To test this, you would make a batchfile with the path of all pleasant average files (subject 1 to  say 16),  followed by the paths of all unpleasant ones (subject 1 to 16), followed by the neutral ones in the same order. Your coefficients would be : -1 -1 2,  indicating that both the unpleasant ones and the pleasant ones are more negative than the neutral ones.

Contrasts, like T-Tests and the ANOVA, so far can only be calculated for equal cell sizes, therefore you have to specifiy an equal number of average file paths for each condition.