Frequency responses of headphones modulate alpha brain oscillations related to auditory processing

Abstract

The perception of sound can differ significantly, regardless of its physical properties. The frequency content of a sound can provoke different psychoacoustic effects on humans, and simultaneously, it modulates differently brain oscillations. Audio devices such as headphones are variables that have not been taken into consideration in many studies concerning acoustic therapies, which strongly depend on the transmission means. Headphones become a fundamental key in acoustic treatments since they are responsible for transmitting auditory stimuli. It is known that the frequency response of audio devices can change the frequency content of a signal. However, it is still unknown if their limited (or even inappropriate) functioning could affect acoustic therapy effectiveness. Therefore, the present work aims to analyze alpha (resonance frequency at which neurons decode auditory information) brain oscillations in healthy individuals when listening to the same sound but through different frequency responses of headphones. For this purpose, the frequency responses of three headphone models were firstly obtained: Atvio® supra-aural headphones (ATVIO), Shure® SRH1840 circum-aural headphones (SHURE), and Apple® EarPods® intra-aural headphones (APPLE). The estimated frequency responses showed that ATVIO and APPLE headphones presented a major difference in comparison with an ideal frequency response (same gain at every frequency of the headphone bandwidth, i.e., a flat frequency response). Then, inverse filters on the difference of the responses were implemented. Finally, the alpha brain oscillations of 29 individuals were analyzed while they were listening to pink noise through the filters of the three models. The findings suggested that the three headphones modulated alpha brain oscillations accordingly their frequency response. Namely, mapping of alpha brain oscillations for ATVIO and APPLE headphones reflected lower neural activity associated with decoding of auditory information, possibly due to the loss of gain at different frequencies. In contrast, SHURE headphones, which presented a flatter frequency response, reflected higher neural activity related to decoding and interpretation of acoustic information since frequency response was much less affected.