title: Inferior frontal sensitivity to common speech sounds is amplified by increasing word intelligibility.
abstract: The left inferior frontal gyrus (LIFG) exhibits increased responsiveness when people listen to words composed of speech sounds that frequently co-occur in the English language (Vaden, Piquado, & Hickok, 2011), termed high phonotactic frequency (Vitevitch & Luce, 1998). The current experiment aimed to further characterize the relation of phonotactic frequency to LIFG activity by manipulating word intelligibility in participants of varying age. Thirty six native English speakers, 19-79 years old (mean=50.5, sd=21.0) indicated with a button press whether they recognized 120 binaurally presented consonant-vowel-consonant words during a sparse sampling fMRI experiment (TR=8 s). Word intelligibility was manipulated by low-pass filtering (cutoff frequencies of 400 Hz, 1000 Hz, 1600 Hz, and 3150 Hz). Group analyses revealed a significant positive correlation between phonotactic frequency and LIFG activity, which was unaffected by age and hearing thresholds. A region of interest analysis revealed that the relation between phonotactic frequency and LIFG activity was significantly strengthened for the most intelligible words (low-pass cutoff at 3150 Hz). These results suggest that the responsiveness of the left inferior frontal cortex to phonotactic frequency reflects the downstream impact of word recognition rather than support of word recognition, at least when there are no speech production demands.
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Medical University of South Carolina, Charleston, SC 29425-5500, United States. vaden@musc.edu
authors.forename: Kenneth I
authors.initials: KI
authors.lastname: Vaden
authors.forename: Stefanie E
authors.initials: SE
authors.lastname: Kuchinsky
authors.forename: Noam I
authors.initials: NI
authors.lastname: Keren
authors.forename: Kelly C
authors.initials: KC
authors.lastname: Harris
authors.forename: Jayne B
authors.initials: JB
authors.lastname: Ahlstrom
authors.forename: Judy R
authors.initials: JR
authors.lastname: Dubno
authors.forename: Mark A
authors.initials: MA
authors.lastname: Eckert
mesh_terms: D000161:Acoustic Stimulation; D000293:Adolescent; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001931:Brain Mapping; D005260:Female; D005625:Frontal Lobe / Q000098:blood supply / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood; D010700:Phonetics; D011571:Psychoacoustics; D011597:Psychomotor Performance; D013016:Sound; D013067:Speech Perception / Q000502:physiology*; D013069:Speech Reception Threshold Test; D014825:Vocabulary; D055815:Young Adult
chemical_list: D010100:Oxygen