This work was partially supported by a grant from JSPS KAKENHI Grant Number JP17K00209. The author thanks Takayuki Hoshino and Kazuhiro Shigeta for technical assistance.

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
<ol>
	<li>Setup of the Reversed Audition System without a Participant 
	<ol>
		<li>Prepare a linear pulse-code-modulation (LPCM) recorder, binaural microphones, and binaural in-ear earphones.</li>
		<li>Con...

<ol>
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The author has nothing to disclose.

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 audition11,12,13,<sup cl...

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 vision1,2,3,4,5 or up-down reversed vision6,7. Furthermore, exposure to such vision from a few days to more than a month has revealed perceptual and behavioral adaptation1,2,3,4,5,6,7 (e.g., capability to ride a bicycle2,5,7). Moreover, periodic measurements of the brain activity using neuroimaging techniques, such as electroencephalography (EEG)1, magnetoencephalography (MEG)3, and functional magnetic resonance imaging (fMRI)2,4,5,7, have detected changes in the neural activity underlying the adaptation (e.g., bilateral visual activation for unilateral visual stimulation4,5). Although the participant&#39;s appearance becomes strange to some extent and great care is needed for the observer to maintain the participant&#39;s safety, reversed vision with prisms provides precise three-dimensional (3D) visual information without any delay in a wearable manner. Therefore, the methodology for uncovering the mechanism of environmental adaptability is relatively established in the visual domain.
In 1879, Thompson proposed a concept of pseudophone, &#34;an instrument for investigating the laws of binaural audition by means of the illusions it produces in the acoustic perception of space&#34;8. However, in contrast to the visual cases1,2,3,4,5,6,7, few attempts have been made to study the adaptation to unusual auditory spaces, and no noticeable knowledge has been obtained to date. Despite a long history of developing virtual auditory displays9,10, wearable apparatuses for controlling 3D audition have rarely been developed. Hence, only a few reports examined the adaptation to left-right reversed audition. One traditional apparatus consists of a pair of curved trumpets that are crossed and inserted into a participant&#39;s ear canals in a contrariwise manner11,12. In 1928, Young first reported the use of these crossed trumpets and wore them continuously for 3 days at most or a total of 85 h to test adaptation to left-right reversed audition. Willey et al.12 retested the adaptation in three participants wearing the trumpets for 3, 7, and 8 days, respectively. The curved trumpets easily provided left-right reversed audition, but had an issue with the reliability of spatial accuracy, wearability, and strange appearance. A more advanced apparatus for the reversed audition is an electronic system in which left and right lines of head/earphones and microphones are reversely connected13,14. Ohtsubo et al.13 achieved auditory reversal using the first ever binaural headphone-microphones that were connected to a fixed amplifier and evaluated its performance. More recently, Hofman et al.14 cross-linked complete-in-canal hearing aids and tested adaptation in two participants that wore the aids for 49 h in 3 days and 3 weeks, respectively. Although these studies have reported high performance of sound source localization in the front auditory field, the sound source localization in the backfield and a potential delay of electrical devices have never been evaluated. Especially in Hofman et al.&#39;s study, the spatial performance of the hearing aids was guaranteed for the front 60&#176; in the head-fixed condition and for the front 150&#176; in the head-free condition, suggesting unknown omniazimuth performance. Moreover, the exposure period may be too short to detect phenomena related to the adaptation as compared with the longer cases of reversed vision2,4,5. None of these studies have measured brain activity using neuroimaging techniques. Therefore, the uncertainty in spatiotemporal accuracy, the short exposure periods, and the non-utilization of neuroimaging could be reasons for the small number of reports and the limited amount of knowledge on adaptation to left-right reversed audition.
Thanks to the recent advances in wearable acoustic technology, Aoyama and Kuriki15 succeeded in constructing a left-right reversed 3D audition using only wearable devices that recently became available and achieved the omniazimuth system with high spatiotemporal accuracy. Moreover, approximately a 1-month exposure to reversed audition using the apparatus exhibited some representative results for MEG measurements. Based on this report, we describe, in this article, a detailed protocol to set-up, validate and use the system, and to test the adaptation to left-right reversed audition with the help of neuroimaging that is performed periodically without the system. This approach is effective for uncovering the adaptability of humans to a novel environment in the auditory domain.

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

a method to study adaptation to left-right reversed audition

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&#176; 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.

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&#176; 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 <str...

Watch this Scientific Journal Video about A Method to Study Adaptation to Left-Right Reversed Audition at JoVE.com

A Method to Study Adaptation to Left-Right Reversed Audition

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.

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 ...

This method can be an effective tool for uncovering the adaptability of humans to a novel environment in the auditory domain. The main advantage with this technique is that long-term adaptation to precise left-right reversed audition can be tested in a variable manner in combination with neural imaging. Demonstrating the procedure will be Takayuki Hoshino, a grad student from my laboratory.To begin, prepare the linear pulse code modulation recorder, binaural microphones and binaural in-ear earphones. First, cross-connect the left and right lines of the microphones to the recorder so that left-right reversed analog sound signals are digitalized. Then, connect the left and right lines of the earphones straight through to the recorder so that the reversed digitalized signals are played immediately.Finally, put the bodies of the microphones and the earphones together for each ear with slight isolation by soundproofing materials. Then cover the microphones with dedicated windscreens for suppressing any wind noise. Next, insert rechargeable batteries and a large-capacity, high-speed memory card into the recorder and turn it on.Then place the body of the system into a pocket-sized bag. Instruct the participant to insert the earphones tightly into the ear canals. Then disconnect the lines for the left and right microphones and connect the dominant ear side of the microphone straight through to the recorder.Now, have them repetitively take off and put on the dominant ear side of the system while adjusting the sound volume of the recorder. This makes the subjective loudness of the reversed sounds equal. Ah, ah.Check the loudness for the non-dominant ear, as well. Then reconnect all the system lines. Tell the participant that, during exposure, they should follow the same calibration procedure whenever they set up the system again.Prior to reversed audition exposure, have the participant thoroughly practice the task that will be used during the neuroimaging experiments. A selective reaction time task can be used. Use a Psychophysics software Toolbox to present 1000 Hertz sounds at 65 decibels sound pressure level for 0.1 seconds, played 80 times per block.Also use an interstimulus interval of 2.5 to 3.5 seconds, played pseudorandomly in either ear. The task should consist of two compatible and two incompatible blocks. In the compatible condition, the participant should respond immediately to the sound with the index finger on the same side of their body as the sound.This should be alternated with the incompatible condition in which the participant responds immediately to the sound with the index finger on the opposite side of their body. Before the exposure to reversed audition, conduct a neuroimaging experiment using the trained task. Record either MEG or EEG responses, as well as the left and right finger responses.To begin exposure, provide the participant with a sufficient number of spare rechargeable batteries and large-capacity, high-speed memory cards so they can replace them as needed. Then, remind them repeatedly of their right to quit the exposure at any time and instruct them to wear, calibrate and check the reversed audition system by themselves during the exposure period. The participant should perform daily life activities while wearing the system continuously for approximately a month, except while sleeping, bathing, neuroimaging or during an emergency.When removed, the system should be immediately replaced with earplugs without producing any sound while in a silent area. The batteries and memory cards should also be replaced routinely, before battery exhaustion and memory overcapacity. To facilitate adaptation, the participant should experience situations involving high auditory input, such as playing video games, walking in a shopping mall or a campus and having a conversation with more than two persons for as long as possible.They should also keep a diary or provide a subjective report to an observer as often as possible, detailing perceptual and behavioral changes, experienced events or any other details. During approximately a one month exposure to reversed audition, conduct neuroimaging experiments under the trained task every week without the reversed audition system in exactly the same way as in the preexposure experiment. Finally, after the target exposure period, the participant should take off the reversed audition system.One week after exposure had ended, conduct a final neuroimaging experiment under the trained task. This figure shows the sound source localization in directions over 360 degrees before and immediately after putting on the left-right reversed audition system in six participants. Here, cosine similarity between perceptual angles and sine-regulated physical angles in the normal and reversed conditions are plotted against unregulated physical angles.And here, we see cosine similarity between perceptual angles in the reversed condition and oppositely-arranged perceptual angles in the normal condition plotted against physical angles. This figure shows changes in behavioral and neural responses during the selective reaction time task before, during and after exposure in one participant. Yellow zones indicate a period exposed to left-right reversed audition.Mean reaction times for the stimulus response compatible and incompatible conditions are seen here, while here we see left and right auditory N1m intensities for stimulus response compatible and incompatible conditions as evaluated by minimum norm estimates of MEG data. This figure shows auditory motor functional connectivity as tested by Granger causality tests during the selective reaction time task in two participants. The left and right motor and auditory areas are shown.Red, yellow or lack of arrows indicate the number of participants who showed significance at a threshold of P less than 0.05. After watching this video, you should have a good understanding of how to study left-right reversed audition as a tool to uncover the adaptability of humans to a novel auditory environment.

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6.3K visualizações.  Keio University. Este método pode ser uma ferramenta eficaz para descobrir a adaptabilidade dos seres humanos a um novo ambiente no domínio auditivo. A principal vantagem com esta técnica é que a adaptação a longo prazo à audição precisa da esquerda para a direita pode ser testada de forma variável em combinação com a imagem neural. Demonstrando o procedimento será Takayuki Hoshino, um estudante de pós-graduação do meu laboratório.Para começar, prepare o gravador de modulação de có...