Neural mechanism of reading: Investigating rapid feedforward-feedback interaction

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DESCRIPTION (provided by applicant): My long-term goal is to advance knowledge about the cognitive and neural mechanisms of human language comprehension. The proposed research focuses specifically on visual word recognition. Progress toward understanding visual word recognition is critical to understanding the mechanisms of skilled reading and its disordered states. I propose to use scalp-recorded event- related potentials (ERPs) to investigate rapid feed forward-feedback dynamics between low-level word-form and higher-level lexical representations during the initial 200 msec of word recognition. Numerous prior ERP studies find that the N400 ERP component (approximately 250-500 msec post- stimulus onset) is sensitive to variables related to lexical access or integration. Most existing work has suggested that processing prior to the N400 is dedicated to lower-level sensory analysis of the visual word form. My recent work has reported novel evidence of rapid feedforward-feedback interactions between low-level word-form and higher-level representations during word recognition. We found enhancement of the P1 component of the ERP 130 msec after stimulus onset (P130 effect) by pseudowords that minimally malformed a contextually appropriate real word (e.g., "She measured the flour so she could bake a cake ..."). Later effects, on the N170 rather than the P1, were elicited by pseudowords that were contextually unsupported (e.g., "She measured the flour so she could bake a tont ...") and by illegal nonwords (e.g., "She measured the flour so she could bake a srdt ..."). I have explained the P130 effect in terms of rapid access of a lexical representation CAKE from the stimulus "ceke". This high-level activation can then generate top-down excitation of word-form representations ("cake") that conflict with the input "ceke", and the P1 modulation may reflect this conflict. Thus, we infer rapid feedforward-feedback interactions between low-level word- form and higher-level representations. We do not yet know the nature of the higher-level representations that mediate our P130 effects. The proposed series of studies will investigate the role of semantic representations (Specific Aim 1) phonological representations (Specific Aim 2) and lexical frequency (Specific Aim 3) in mediating these effects. This work will illuminate the complex interaction between cognitive processes that serve the rapid recognition of a word within about 1/2 second after the retinal stimulation during skilled reading. Progress in understanding these fundamental processes will set the stage for investigation of individual differences among adults and children in reading processes and can potentially be developed into diagnostic tools for reading disorders.