Symbolic action priming relies on intact neural transmission along the retino-geniculo-striate pathway

Recent psychophysics studies suggest that the behavioral impact of a visual stimulus and its conscious visual recognition underlie two functionally dissociated neuronal processes. Previous TMS studies have demonstrated that certain features of a visual stimulus can still be processed despite TMS-induced disruption of perception. Here, we tested whether symbolic action priming also remains intact despite TMS-induced masking of the prime. We applied single-pulse TMS over primary visual cortex at various temporal intervals from 20 ms to 120 ms during a supraliminal action priming paradigm. This TMS protocol enabled us to identify at what exact time point a TMS-induced activity disruption of primary visual cortex interferes with conscious visual perception of the prime versus (un)conscious behavioral priming of the visual target stimulus. We also introduced spatial uncertainty by presenting visual stimuli either above or below the fixation cross, while the TMS pulse was always targeting the prime presented below fixation. We revealed that TMS over primary visual cortex interferes with both conscious visual perception and symbolic behavioral priming in a temporarily and spatially specific manner, i.e., only when disrupting primary visual cortex at approximately the same temporal stage between 60 and 100 ms after prime onset, and only for those prime stimuli presented below fixation. These findings are in disagreement with the idea of subliminal action priming being mediated by neural pathways bypassing striate cortex, and rather suggest that symbolic action priming relies on an intact neural transmission along the retino-geniculo-striate pathway. The implications of our findings for previous reports of residual visual processing during striate TMS are discussed.