Behavioral Evidence for Attention Selection as Entrained Synchronization Without Awareness

Animal physiological and human neuroimaging studies have established a link between attention and gamma-band (30-90 Hz) oscillations and synchronizations. However, a behavioral link between entrained -gamma-band oscillations and attention has been fraught with technical challenges. In particular, while entrainment at mid-gamma band (40-70 Hz) has been claimed to be privileged in evoking attentional modulations without awareness, the effect may be attributed to display artifacts. Here, by exploiting isoluminant chromatic flicker without luminance modulation and not subject to these artifacts, we tested attentional attraction by chromatic flicker too fast to perceive. Awareness of flicker was subjectively and objectively tested with a high-powered design and evaluated with traditional and Bayesian statistics. Across 2 experiments in human participants. we observed-and also replicated-that 30-Hz chromatic flicker outside mid-gamma band attracted attention, resulting in a facilitation effect at a 50 ms interstimulus interval (ISI) and an inhibition effect at a 500 ms ISI. The attention test was confirmed to be more sensitive to the cue than the direct cue-localization task was. We further showed that these attention effects were absent for 50-Hz chromatic flicker. These results provide strong direct evidence against a privileged role of mid-gamma band in unconscious attention, but are consistent with known cortical responses to chromatic flicker in early visual cortex. Taken together, our findings provide behavioral evidence that entrained synchronization may serve as a mechanism for bottom-up attention selection and that chromatic flicker may offer a fruitful avenue for investigating unconscious processing.