Unveiling stimulus transduction artifacts in auditory steady-state response experiments: Characterization, risks, and mitigation strategies

This scientific paper addresses the potential risk of spurious responses in neuroscientific auditory steady-state response (ASSR) experiments attributed to transduction artifacts. The focus is particularly on click train stimuli, given their spectral content in the frequency range of interest (e.g., 40 Hz). Building upon a pilot experiment demonstrating the existence of the artifact in a phantom head, this study focuses on the characterization of stimulus artifacts in extended measurements with phantoms and the evaluation of associated risks in experiments involving human subjects, where 15 subjects were stimulated by headphones and speakers, which served as a control condition. The investigation is divided into two parts: the first part scrutinizes stimulus artifact properties crucial for mitigation, while the second part assesses risks in ASSR experiments with human subjects based on the characterized artifact. The discussion covers stimulus characterization, experimental setups with phantoms, and experiments with human subjects, exploring potential sources of the artifact, its spatial properties, and the influence of re-referencing, which can suppress a less prominent artifact while significantly increasing the prominent and focused artifact. The results reveal the role of headphone cables as a source of stimulus artifacts, along with the surprising impact of headphone transducers. The study emphasizes the need for careful experimental design. We proposes specific data analyses assessing cross- frequency correlation maps and the topographic structure of the brain response at higher harmonic frequencies of the fundamental 40 Hz component. These steps, if applied appropriately, will prevent misinterpretation of stimulus artifacts as genuine brain responses in ASSR experiments.