Humans and other advanced animals have an impressive capacity to recognize the behavioral significance, or category membership, of a wide range of sensory stimuli. This ability is critical, because it allows us to respond appropriately to the continuous stream of stimuli and events that we encounter in our interactions with the environment. Of course, we are not born with a built-in library of meaningful categories, such as 'tables' and 'chairs,' that we are pre-programmed to recognize. Instead, we learn to recognize the meaning of such stimuli through experience. With National Science Foundation Funding, Dr. David J. Freedman is carrying out studies whose goal is to understand how visual-feature encoding in early visual processing areas is transformed into more meaningful representations at more advanced neuronal processing stages in the brain. The goals of the proposed studies are to compare neuronal representations of visual-motion processing stages across a network of interconnected brain areas in and around the parietal lobe during visual motion categorization tasks. Specifically, one series of experiments compares neuronal responses in two distinct interconnected regions of parietal cortex, the lateral and medial interparietal areas, which are known to be more involved in visual and somatosensory or motor processing, respectively. Activity in these two areas is examined during a categorization task that requires motor decisions to be executed in response to visual stimuli, allowing the relative roles of the two areas in the decision making process to be determined. A second series of experiments is comparing cortical activity in the lateral intraparietal and prefrontal cortices during a novel visual categorization task in which subjects learn multiple independent category rules and apply those rules flexibly and dynamically to incoming visual stimuli. This study gives critical insights into the contributions of frontal and parietal cortex to flexible rule-based categorization. Together, these studies can yield important insights into how learning influences the encoding of visual information and into the roles of interconnected networks of parietal and frontal cortices in visual recognition and decision making.
While much is known about how the brain processes simple sensory features (such as color, orientation, and direction of motion), less is known about how the brain learns and represents the meanings or category of stimuli. A greater understanding of visual learning and categorization is critical for addressing a number of brain diseases and conditions (e.g., stroke, Alzheimer's disease, attention deficit disorder, and schizophrenia) that leave patients impaired in everyday tasks that require visual learning, recognition, and/or evaluating and responding appropriately to sensory information. Dr. Freedman's research is helping to guide the next generation of treatments for these brain-based diseases and disorders by helping to develop a detailed basic understanding of the brain mechanisms that underlie learning, memory and recognition. These studies also have relevance for understanding and addressing learning disabilities, such as attention deficit disorder and dyslexia, which affect a substantial fraction of school age children and young adults. A more detailed understanding of the basic brain mechanisms underlying learning, memory and attention will likely give important insights into the causes and potential treatments for disorders involving these cognitive faculties.
