Thanks for replying and letting me know about the MRML function. 

When using my own data and loading the vtk files with the ShapePopulationViewer, I get basically blank models. As I think about things, I believe my data are in fact failing spherical parameterization. When I do the same thing with the example data,  I am able to see the hippocampus in the viewer. 

Thanks for your help! Now I have to figure out if I can adjust my surfaces to make them spherical.. 

Michael