Conformal in-ear bioelectronics for visual and auditory brain-computer interfaces

Brain-computer interfaces (BCIs) have attracted considerable attention in motor and language rehabilitation. Most devices use cap-based non-invasive, headband-based commercial products or microneedle-based invasive approaches, which are constrained for inconvenience, limited applications, inflammation risks and even irreversible damage to soft tissues. Here, we propose in-ear visual and auditory BCIs based on in-ear bioelectronics, named as Spiral, which can adaptively exploit and engage the auditory meatus under electrothermal actuation to enhance information acquisition. Participants achieve offline accuracies of 95% in 2-target steady state visual evoked potential (SSVEP) BCI classification and type target phrases through calibration-free 40-target online SSVEP speller experiment. Interestingly, ear SSVEPs exhibit significant 2nd harmonic frequencies, indicating that in-ear sensing may be complementary for studying harmonic spatial distributions in SSVEP studies. Moreover, ear-pressed auditory classification accuracy can reach 84% in cocktail party experiments. The Spiral provides innovative concepts for designing 3D flexible bioelectronics and assists the development of biomedical engineering and neural monitoring.