Orthographic influence on spoken word identification: Behavioral and fMRI evidence

The current study investigated behavioral and neuroimaging evidence for orthographic influences on auditory word identification. To assess such influences, the proportion of similar sounding words (i.e. phonological neighbors) that were also spelled similarly (i.e., orthographic neighbors) was computed for each auditorily presented word as the Orthographic-to-Phonological Overlap Ratio (OPOR). Speech intelligibility was manipulated by presenting monosyllabic words in multi-talker babble at two signal-to-noise ratios: + 3 and + 10 dB SNR. Identification rates were lower for high overlap words in the challenging + 3 dB SNR condition. In addition, BOLD contrast increased with OPOR at the more difficult SNR, and decreased with OPOR under more favorable SNR conditions. Both voxel-based and region of interest analyses demonstrated robust effects of OPOR in several cingulo-opercular regions. However, contrary to prior theoretical accounts, no task-related activity was observed in posterior regions associated with phonological or orthographic processing. We suggest that, when processing is difficult, orthographic-to-phonological feature overlap increases the availability of competing responses, which then requires additional support from domain general performance systems in order to produce a single response.