In the first experiment, the participants looked at series of cars presented at different parts of the screen and performed simple position judgments on the images, while their brain activity was being measured using an advanced functional Magnetic Resonance Imaging (fMRI) technique that made it possible to more directly probe neuronal tuning than in previous studies. Investigators found that cars activated a particular region in participants' brains, the lateral occipital cortex, which had also been found by other studies to be important for object recognition.
Then the volunteers were given several hours of training using images of the cars. In these sessions, participants had to learn how to group the cars into two distinct categories. This was easy at first, Riesenhuber said, because the cars were obviously not alike, but then the researchers began to "tighten the screws" by making the two categories increasingly more similar.
"Over the course of the training, the participants got better at finer and finer category discriminations," Riesenhuber said. "This represents a crucial step in category learning where small differences in shape can have a big impact on category labels ?as in the tennis ball and apple example ?and where big differences in shape ?such as between an apple and a banana ?can have no impact on the label, such as when categorizing both as 'fruit'."
Now that the volunteers had learned how to categorize small shape changes, they were shown the cars from the first experiment while again being scanned, allowing the researchers to compare how training had enhanced the brain's ability to process car sha
Source:Georgetown University Medical Center