Figure 1. Population averages at each iteration in the hierarchical model building process.

For each step in the model-building process, axial (top row) and sagittal (bottom row) views are shown. From left to right: The 9-parameter linear, 12-parameter linear, and each of the 6 nonlinear models (from each step outlined in Table 1). Note the improved contrast and structural resolution at each step in the model building process.