For most literate adults, reading feels effortless. However, visual word recognition is a complex process performed by specialized circuits in the brain, and for millions of people it never becomes easy. Even skilled readers have to process a page of text in small chunks, due to poor peripheral vision and inherent capacity limits for sensory information processing. It is difficult to recognize even just two clearly visible words at once. This project investigates the underlying neuronal basis for capacity limits in visual word recognition and how they differ across individuals. Specific research goals: (1) To test the hypothesis that a particular occipito- temporal brain area, the putative `visual word form area' (VWFA), is a bottleneck to word recognition. Observers will view flashing pairs of words in an MRI scanner that records both functional activity and structural connections between brain areas. To trace out the flow of information from early visual cortex into the language system, this study will manipulate which aspects of the stimuli the observers attend to. (2) To vary the task demands in order to hone in on the particular stage of word recognition (e.g., orthographic, lexical) where there is a processing bottleneck. (3) To test the hypothesis that individual differences in reading ability are related to capacity limits in particular processing stages, and to relate those capacity limits to white matter tracts that are hypothesized to control the flow of visual information during reading. Candidate: Dr. Alex White is a postdoctoral researcher seeking to establish himself as a uniquely skilled cognitive neuroscientist and launch his own laboratory to study visual perception and the neural foundations of literacy. In his prior training, he investigated the mechanisms of selective attention with psychophysics, eye-tracking, and fMRI. In his most recent work he discovered that skilled readers can semantically recognize only one word at a time, and now seeks to fully explain that finding. To accomplish these goals he needs more training in advanced neuroimaging, especially diffusion-weighted MRI (dMRI), to assay the white matter tracts in the reading circuitry. The Pathway to Independence Award will allow him to reach his goals by funding additional training at the University of Washington and facilitating his transition to a faculty position. Training plan: Dr. White has assembled a first-rate team of mentors: Dr. Jason Yeatman, who develops sophisticated imaging methods to study the neural circuits related to reading and dyslexia; Dr. Geoff Boynton, an expert in fMRI and the effects of attention in human visual cortex; and Dr. John Palmer, who develops mathematical models for capacity limits in perception. In the K99 phase of this award, these mentors will train Dr. White in advanced fMRI analysis techniques, dMRI and modeling. They will support the execution of the first set of proposed studies and prepare him to become an effective principal investigator. When he carries on this work independently in his own lab, he hopes to open new avenues of applied research that will alleviate reading impairments in diverse populations.
The ability to recognize written words depends on healthy functioning of a specialized network of brain regions. This project uses advanced neuroimaging combined with behavioral tests to determine how much information that network can process in parallel, and how its properties differ between good and poor readers. A full understanding of individual differences in neural processing capacity will facilitate the diagnosis and treatment of specific reading impairments such as dyslexia.
