The cortical mechanisms of divided attention in word recognition

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 DESCRIPTION (provided by applicant): Written language is a crowning achievement of the human brain: it allows the thoughts of one person to flow into the mind of another despite great time and distance between them. For most readers, this information transfer happens effortlessly. Nevertheless, there are limits to how much text can be understood at once; for instance, you do not yet know what the next sentence says. This project uses a combination of behavioral testing and brain imaging to answer the following questions: Is it possible to recognize two words simultaneously? If not, what internal bottlenecks constrain the processing of printed text? Human observers will make judgments about various aspects of words that are flashed simultaneously on both sides of a computer screen. In addition, the observers will either focus attention on one location or divide attention between words at both locations. While they do that, their brain activity will be recorded with functional magnetic resonance imaging. Of particular interest are the visual areas of the brain, including one that responds selectively to words. Some brain areas may respond less strongly when attention is divided than focused, indicating that those areas play a role in determining behavioral accuracy. Furthermore, by varying the demands of the task, this project will uncover the particular stages of visual word processing-from extracting the features of individual letters to retrieving the semantic meaning-that impose the greatest limits on reading ability. The results will enhance our understanding of the limitations of the human brain, setting the stage for further research applied to learning disabilities. Dyslexia impairs reading for up to 10 percent of the population, and it may have multiple causes including difficulties with word sounds (phonology). In some theories, reading is slowed by failures to select small chunks of text in the correct order, or by improper division of attention across the page. Therefore, by studying how visual attention works in typical readers, this project may elucidate the mechanisms of dyslexia and impairments caused by brain damage. That knowledge can help design interventions targeted to each individual according to the challenges he or she faces.