A Method to Study Adaptation to Left-Right Reversed Audition

Summary

The present study proposes a protocol to investigate the adaptation to left-right reversed audition achieved only by wearable devices, using neuroimaging, which can be an effective tool for uncovering the adaptability of humans to a novel environment in the auditory domain.

Abstract

An unusual sensory space is one of the effective tools to uncover the mechanism of adaptability of humans to a novel environment. Although most of the previous studies have used special spectacles with prisms to achieve unusual spaces in the visual domain, a methodology for studying the adaptation to unusual auditory spaces has yet to be fully established. This study proposes a new protocol to set-up, validate, and use a left-right reversed stereophonic system using only wearable devices, and to study the adaptation to left-right reversed audition with the help of neuroimaging. Although individual acoustic characteristics are not yet implemented, and slight spillover of unreversed sounds is relatively uncontrollable, the constructed apparatus shows high performance in a 360° sound source localization coupled with hearing characteristics with little delay. Moreover, it looks like a mobile music player and enables a participant to focus on daily life without arousing curiosity or drawing attention of other individuals. Since the effects of adaptation were successfully detected at the perceptual, behavioral, and neural levels, it is concluded that this protocol provides a promising methodology for studying adaptation to left-right reversed audition, and is an effective tool for uncovering the adaptability of humans to a novel environments in the auditory domain.

Introduction

Adaptability to a novel environment is one of the fundamental functions for humans to live robustly in any situation. One effective tool for uncovering the mechanism of environmental adaptability in humans is an unusual sensory space that is artificially produced by apparatuses. In the majority of the previous studies dealing with this topic, special spectacles with prisms have been used to achieve left-right reversed vision^1,2,3,4,5 or up-down reversed vision^6,

Protocol

All methods described here have been approved by the Ethics Committee of Tokyo Denki University. For every participant, informed consent was obtained after the participant received a detailed explanation of the protocol.

1. Setup of the Left-Right Reversed Audition System

1. Setup of the Reversed Audition System without a Participant
   1. Prepare a linear pulse-code-modulation (LPCM) recorder, binaural microphones, and binaural in-ear earphones.
   2. Connect the left and right lines of the microphones crossly to the LPCM recorder so that left-right reversed analogue sound signals are digitalized. More....

Results

The representative results shown here are based on Aoyama and Kuriki¹⁵. The present protocol achieved left-right reversed audition with high spatiotemporal accuracy. Figure 1 shows the sound source localization in directions over 360° before and immediately after putting on the left-right reversed audition system (Figure 1A), in six participants, as indicated by the cosine similarity. As shown in

Discussion

The proposed protocol aimed to establish a methodology for studying adaptation to left-right reversed audition as an effective tool for uncovering the adaptability of humans to a novel auditory environment. As evidenced by the representative results, the constructed apparatus achieved left-right reversed audition with high spatiotemporal accuracy. Although the previous apparatuses for reversed audition^11,12,13,

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Linear pulse-code-modulation recorder	Sony	PCM-M10
Binaural microphones	Roland	CS-10EM
Binaural in-ear earphones	Etymotic Research	ER-4B
Digital angle protractor	Wenzhou Sanhe Measuring Instrument	5422-200
Plane-wave speaker	Alphagreen	SS-2101
Video camera	Sony	HDR-CX560
MATLAB	Mathworks	R2012a, R2015a	R2012a for stimulation and R2015a for analysis
Psychophysics Toolbox	Free	Version 3	http://psychtoolbox.org
Insert earphones	Etymotic Research	ER-2
Magnetoencephalography system	Neuromag	Neuromag-122 TM
Electroencephalography system	Brain Products	acti64CHamp
MNE	Free	MNE Software Version 2.7, MNE 0.13	https://martinos.org/mne/stable/index.html
The Multivariate Granger Causality Toolbox	Free	mvgc_v1.0	http://www.sussex.ac.uk/sackler/mvgc/