Configure mkcontrast-sess

Contrasts are embodiments of hypotheses that you want to test. They are linear combinations of conditions. In order to construct a contrast, you need to know the numeric ID associated with each condition; this is specified in your paradigm file.

Suppose, for example, your par-files for the LDT experiment were encoded with the following conditions:

1 nonword
2 low-frequency word
3 high-frequency word

Contrasts between conditions are vector weightings of each condition.

The key thing is that the activated and contrast weightings must sum to zero. Continuing with this example, to configure the words > nonwords contrast for the analysis specified by the previous call to mkanalysis-sess, you would run the following command within your $SUBJECTS_DIR:

mkcontrast-sess -analysis ldt.lh -contrast words-v-nonwords -a 2 -a 3 -c 1

Pertinent to some of our borrowed data, we have the following conditions for the children's dyslexia study:

1 O+P+
2 O+P-
3 O-P+
4 O-P-
5 Null (Fixation)
6 Perceptual

Contrasts between all first four lexical conditions and the fixation condition (i.e., LEX-FIX) would be coded:

mkcontrast-sess -analysis booth500.sm6.lh -contrast LEX_v_FIX -a 2 -a 3 -c 1