Alpha and beta rhythms differentially support the effect of symbols on visual object recognition

Hearing spoken words can enhance visual object recognition, detection and discrimination. Yet, the mechanism underlying this facilitation is incompletely understood. On one account, words would not bias visual processes at early levels, but rather interact at later decision-making stages. More recent proposals posit that words can alter visual processes at early stages by activating category-specific priors in sensory regions. A prediction of this account is that top-down priors evoke changes in occipital areas before the presentation of visual stimuli. Here, we tested the hypothesis that neural oscillations can serve as a mechanism to activate language-mediated visual priors. Participants performed a cue-picture matching task where cues were either spoken words, in their native or second language, or natural sounds, while EEG and reaction times were recorded. Behaviorally, we replicated the previously reported label-advantage effect, with images cued by words being recognized faster than those cued by natural sounds. A time-frequency analysis of cue-target intervals revealed that this label-advantage was associated with enhanced power in posterior alpha (9-11 Hz) and beta oscillations (17-19 Hz), both of which were larger when the image was preceded by a word compared to a natural sound. Prestimulus alpha and beta rhythms were correlated with reaction time performance, yet they appeared to operate in different ways. Reaction times were faster when alpha power increased, but slowed down with enhancement of beta oscillations. These results suggest that alpha and beta rhythms work in tandem to support language-mediated visual object recognition, while showing an inverse relationship to behavioral performance.