One hundred years ago Bleuler (1911) described schizophrenia as being characterized by a lack of connections between associations in memory. Suddath, Christison, Torrey, Casanova, and Weinberger (1990) ran an interesting study on this hypothesis. The hippocampus has been suggested as playing an important role in memory storage and retrieval, and it is reasonable to ask if differences in hippocampal structures (particularly size) could play a role in schizophrenia. Suddath obtained MRI scans on the brains of 15 schizophrenic individuals and their monozygotic (identical) twins. They measured the volume of each brain’s left hippocampus. Suddath used monozygotic twin pairs in an effort to control as many variables as possible that influence the volume of cortical and subcortical structures. This, in turn, reduces the amount of variance to be explained. The results appear below as taken from Ramsey and Schafer (1997).

If you plot the difference scores for these 15 twin pairs, as shown in Figure 20.1, you will note that the distribution is far from normal. Run a randomization test on the hypothesis that the volume of the hippocampus in the left hemisphere is the same for both conditions.

I frequently ask you to use SPSS or R to solve a problem. You should have no problem with SPSS if you stick with the “Legacy” analyses. You should be able to use R by modifying the code that I give on the Web page for this chapter: http://www.uvm .edu/~dhowell/fundamentals9/Supplements/Chapter20R.html

Transcribed Image Text:

Pair Normal Schizophrenic Difference 1 1.94 1.27 0.67 23 1.45 1.63 -18 1.56 1.47 0.09 4 1.58 1.39 0.19 569 2.06 1.93 0.13 1.66 1.26 0.40 1.75 1.71 0.04