For the first time, researchers could discover which specific parts of the brain were activated when subjects performed particular tasks. We can begin to explain the behavioral results obtained by cognitive investigators if images rely on such structures. To test the explanation, our group at the Massachusetts General Hospital PET laboratory took advantage of a finding by Peter Fox, now of the University of Texas at Austin, and his colleagues. They asked subjects to look at different-sized patterns while their brains were scanned, and found that the larger the pattern, the more anterior the activation was along the calcarine sulcus. PET results of visualizing letters at two sizes.
Brighter colors indicate more activation.
Courtesy of Stephen Kosslyn. We performed the imagery analog of their experiment. We asked subjects to close their eyes and listen to the names of letters. In one set of trials, the subjects were to visualize uppercase letters, one at a time, as small as possible, and wait for a question. In another set of trials, they were asked to visualize each letter as large as possible, without having it overflow, and then to evaluate the image.