The Interplay between the Oculomotor and Auriculomotor System: Implications for Human-Machine Interfaces

Auricular muscles, which are located discreetly around the ear, have the potential to be used in human-machine interfaces (HMIs), because voluntary contraction can generate very strong and reliable control signals. Significant involuntary co-activation between the oculomotor- and auriculomotor system during large, maximal horizontal eye gaze deflections is an established phenomenon. However, activation of auricular muscles during small eye movements, which are expected to occur in realistic applications of HMIs are largely unexplored. Therefore, this study aims to investigate the influence of small, but systematic horizontal eye movements (<35<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup>) on several auricular muscles. Electromyograms (EMGs) of four different auricular muscles were recorded in 27 participants. Results show that activity of most auricular muscles increases significantly during small eye movements. Furthermore, when comparing left and right auricular muscles, activity was often significantly larger at the muscle ipsilateral to the gaze direction. However, while effects were statistically significant, EMGs increased mostly around 5–10%, which is far below what is expected during voluntary contraction of auricular muscles. Nevertheless, the results imply that, especially automated or machine learning based approaches to utilize auricular muscles in HMIs, or training paradigms to obtain voluntary control of auricular muscles, should consider small, systematic eye movements as a potential confounding factor.