The experiment involves an associative memory task. The subject is
shown one of 4 stimulus types. Each stimulus has 5 words in the
following pattern:

                         targetword
                   testword1     testword3
                   testword2     testword4

The subject is asked to choose which test word is most related to the
target word. 

By design, the target word is either highly related or loosely related
to one of the test words.

Sometimes there are four test words and sometimes there are two test
words and two "words" with just X's in them.

This makes 4 conditions:

1. H2 - highly related, two words/two X's
2. H4 - highly related, four words
3. L2 - loosely related, two words/two X's
4. L4 - loosely related, four words

The contrast (L2+L4) - (H2-H4) should show activity in the left frontal
region.
