title: Neural correlates of top-down letter processing.
abstract: This fMRI study investigated top-down letter processing with an illusory letter detection task. Participants responded whether one of a number of different possible letters was present in a very noisy image. After initial training that became increasingly difficult, they continued to detect letters even though the images consisted of pure noise, which eliminated contamination from strong bottom-up input. For illusory letter detection, greater fMRI activation was observed in several cortical regions. These regions included the precuneus, an area generally involved in top-down processing of objects, and the left superior parietal lobule, an area previously identified with the processing of valid letter and word stimuli. In addition, top-down letter detection also activated the left inferior frontal gyrus, an area that may be involved in the integration of general top-down processing and letter-specific bottom-up processing. These findings suggest that these regions may play a significant role in top-down as well as bottom-up processing of letters and words, and are likely to have reciprocal functional connections to more posterior regions in the word and letter processing network.
authors.affiliation: Department of Biomedical Engineering, School of Computer and Information Technology, Beijing Jiaotong University, Beijing, China.
authors.forename: Jiangang
authors.initials: J
authors.lastname: Liu
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.forename: Hongchuan
authors.initials: H
authors.lastname: Zhang
authors.forename: Cory A
authors.initials: CA
authors.lastname: Rieth
authors.forename: David E
authors.initials: DE
authors.lastname: Huber
authors.forename: Wu
authors.initials: W
authors.lastname: Li
authors.forename: Kang
authors.initials: K
authors.lastname: Lee
authors.forename: Jie
authors.initials: J
authors.lastname: Tian
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D000293:Adolescent; D000328:Adult; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000098:blood supply / Q000502:physiology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D009483:Neuropsychological Tests; D010100:Oxygen / Q000097:blood; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D017603:Signal Detection, Psychological / Q000502:physiology; D055815:Young Adult
chemical_list: D010100:Oxygen