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This protocol is designed to explore underlying learning-related electrophysiological changes in subjects with profound deafness after a short training period in audio-tactile sensory substitution by applying the event-related potential technique.
This paper examines the application of electroencephalogram-based methods to assess the effects of audio-tactile substitution training in young, profoundly deaf (PD) participants, with the aim of analyzing the neural mechanisms associated with vibrotactile complex sound discrimination. Electrical brain activity reflects dynamic neural changes, and the temporal precision of event-related potentials (ERPs) has proven to be key in studying time-locked processes while performing behavioral tasks that involve attention and working memory.
The current protocol was designed to study electrophysiological activity in PD subjects while they performed a continuous performance task (CPT) using complex-sound stimuli, consisting of five different animal sounds delivered through a portable stimulator system worn on the right index finger. As a repeated-measures design, electroencephalogram (EEG) recordings in standard conditions were performed before and after a brief training program (five 1 h sessions over 15 days), followed by offline artifact correction and epoch averaging, to obtain individual and grand-mean waveforms. Behavioral results show a significant improvement in discrimination and a more robust P3-like centroparietal positive waveform for the target stimuli after training. In this protocol, ERPs contribute to the further understanding of learning-related neural changes in PD subjects associated with audio-tactile discrimination of complex sounds.
Early profound deafness is a sensory deficit that strongly impacts oral language acquisition and the perception of environmental sounds that play an essential role in navigating everyday life for those with normal hearing. A preserved and functional auditory sensory pathway allows us to hear footsteps when someone is approaching out of visual range, react to oncoming traffic, ambulance sirens, and security alarms, and respond to our own name when someone needs our attention. Audition is, therefore, a vital sense for speech, communication, cognitive development, and timely interaction with the environment, including the perception of potential threats in one's surroundings. For decades, the viability of audio-tactile substitution as an alternative sound perception method with the potential to complement and facilitate language development in severely hearing-impaired individuals has been explored with limited results1,2,3. Sensory substitution aims to provide users with environmental information through a human sensory channel different from the one normally used; it has been demonstrated to be possible across different sensory systems4,5. Specifically, audio-tactile sensory substitution is achieved when skin mechanoreceptors can transduce the physical energy of soundwaves that compose auditory information into neuronal excitation patterns that can be perceived and integrated with the somatosensory pathways and higher order somatosensory cortical areas6.
Several studies have demonstrated that profoundly deaf individuals can distinguish musical timbre solely through vibrotactile perception7 and discriminate between same-sex speakers using spectral cues of complex vibrotactile stimuli8. More recent findings have shown that deaf individuals concretely benefitted from a brief, well-structured audio-tactile perception training program, as they significantly improved their ability to discriminate between different pure-tone frequencies9 and between pure-tones with different temporal duration10. These experiments used event-related potentials (ERPs), graph connectivity methods, and quantitative electroencephalogram (EEG) measurements to depict and analyze functional brain mechanisms. However, the neural activity associated with the discrimination of complex environmental sounds has not been examined prior to this paper.
ERPs have proven useful for studying time-locked processes, with incredible time resolution in the order of milliseconds, while performing behavioral tasks that involve attention allocation, working memory, and response selection11. As described by Luck, Woodman, and Vogel12, ERPs are intrinsically multidimensional processing measures and are therefore well suited to separately measure the subcomponents of cognition. In an ERP experiment, the continuous ERP waveform elicited by the presentation of a stimulus can be used to directly observe neural activity that is interposed between the stimulus and the behavioral response. Other advantages of the technique, such as its cost-effectiveness and non-invasive nature, make it a perfect fit to study the precise time course of cognitive processes in clinical populations. Furthermore, ERP tools applied in a repeated-measures design, in which patients' electrical brain activity is recorded more than once to study changes in electrical activity after a training program or intervention, provide further insight into neural changes over time.
The P3 component, being the most extensively researched cognitive potential13, is currently recognized to respond to all kinds of stimuli, most apparently to stimuli of low probability, or of high intensity or significance, or ones that require some behavioral or cognitive response14. This component has also proven extremely useful in evaluating general cognitive efficiency in clinical models15,16. A clear advantage of assessing changes in the P3 waveform is that it is an easily observable neural response because of its greater amplitude compared to other smaller components; it has a characteristic centroparietal topographical distribution and is also relatively easy to elicit using the appropriate experimental design17,18,19.
In this context, the aim of this study is to explore the learning-related electrophysiological changes in patients with profound deafness after training for a short period in vibrotactile sound discrimination. In addition, ERP tools are applied to depict the functional brain dynamic underlying the temporary engagement of the cognitive resources demanded by the task.
The study was reviewed and approved by the Neuroscience Institute's Ethics Committee (ET062010-88, Universidad de Guadalajara), ensuring all procedures were conducted in accordance with the Declaration of Helsinki. All participants agreed to participate voluntarily and gave written informed consent (when underaged, parents signed consent forms).
1. Experimental design
2. Participant selection
3. Pre-training EEG recording session
4. Audio-tactile sensory substitution training program
5. Post-training EEG recording session
6. EEG analysis
NOTE: The EEG acquisition steps were done using the EEG recording software, and the EEG processing steps were done using a separate EEG analysis software.
To illustrate how the effect of the audio-tactile sensory substitution discrimination training in PD individuals can be assessed by evaluating changes in P3 in a group of 17 PD individuals (mean age = 18.5 years; SD = 7.2 years; eight females and 11 males), we created several figures to portray the ERP waveforms. The results shown in the ERP plots reveal changes in a P3-like centroparietal positive waveform which is more robust for the target stimuli after training. In the pre-training condition, ERPs suggest that the T ...
Using ERP tools, we designed a protocol to observe and evaluate the gradual development of vibrotactile discrimination skills for distinguishing vibrotactile representations of different pure tones. Our prior work has demonstrated that vibrotactile stimulation is a viable alternative sound perception method for profoundly deaf individuals. However, because of the complexity of natural sounds compared to pure tones, the potential for language sound discrimination warrants a separate exploration.
We confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.
We thank all the participants and their families, as well as the institutions that made this work possible, in particular, Asociación de Sordos de Jalisco, Asociación Deportiva, Cultural y Recreativa de Silentes de Jalisco, Educación Incluyente, A.C., and Preparatoria No. 7. We also thank Sandra Márquez for her contribution to this project. This work was funded by GRANT SEP-CONACYT-221809, GRANT SEP-PRODEP 511-6/2020-8586-UDG-PTC-1594, and the Neuroscience Institute (Universidad de Guadalajara, Mexico).
Name | Company | Catalog Number | Comments |
Audacity | Audacity team | audacityteam.org | Free, open source, cross-platform audio editing software |
Audiometer | Resonance | r17a | |
EEG analysis Software | Neuronic , S.A. | ||
EEG recording Software | Neuronic , S.A. | ||
Electro-Cap | Electro-cap International, Inc. | E1-M | Cap with 19 active electrodes, adjustable straps and chest harness. |
Electro-gel | Electro-cap International, Inc. | ||
External computer speakers | |||
Freesound | Music technology group | freesound.org | Database of Creative Commons Licensed sounds |
Hook and loop fastner | Velcro | ||
IBM SPSS (Statistical Package for th Social Sciences) | IBM | ||
Individual electrodes | Cadwell | Gold Cup, 60 in | |
MEDICID-5 | Neuronic, S.A. | EEG recording equipment (includes amplifier and computer). | |
Nuprep | Weaver and company | ECG & EEG abrasive skin prepping gel | |
Portable computer with touch screen | Dell | ||
SEVITAC-D | Centro Camac, Argentina. Patented by Luis Campos (2002). | http://sevitac-d.com.ar/ | Portable stimulator system is worn on the index-finger tip and it consists of a tiny flexible plastic membrane with a 78.5 mm2 surface area that vibrates in response to sound pressure waves via analog transmission. It has a sound frequency range from 10 Hz to 10 kHz. |
Stimulus presentation Software Mindtracer | Neuronics, S.A. | ||
Stimulation computer monitor and keyboard | |||
Tablet computer | Lenovo | ||
Ten20 Conductive Neurodiagnostic Electrode paste | weaver and company |
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