Tuesday, October 22, 2013

Musical Training Enhances Neural Processing of Binaural Sounds

Musical Training Enhances Neural Processing of Binaural Sounds

Source:
Parbery-Clark, A., Strait, D.L., Hittner, E., Kraus, N. 2013 Musical Training Enhances Neural Processing of Binaural Sounds. The Journal of Neuroscience, 33(42):16741-16747.
http://www.jneurosci.org/content/33/42/16741.short

Summary:

 In this paper Parbery-Clark et al address their hypothesis that musicians' strengthened auditory processing is related to enhanced diotic listening, and that this enhancement relates to their superior hearing in noise.

 Binaural hearing refers to auditory processing of incoming sounds from both ears, and is critical in order to hear within loud, complex listening environments. The human brain can detect differences in incoming sounds between the left and right ears on the order of tens to hundreds of microseconds (10^-6 seconds!). This is crucial for hearing in noisy environments because the auditory system uses timing mechanisms to segregate concurrent sounds according to slight differences in location, pitch, and sound quality. Diotic hearing is binaural hearing in which both ears experience the same sounds at the same time.

 Musicians appear to have an over-average ability to manage complex auditory environments and have increased perceptual learning abilities. Studies suggest that music training may be linked to strengthened perception, and neural encoding of speech in the presence of noise. These enhanced abilities, however, have never been directly compared in monaural (hearing sound through only one ear) and diotic circumstances.

 In lay terms: this experiment set out to answer the question of whether or not these enhanced auditory processing abilities in musicians involved diotoic hearing specifically.

 In order to address this question, Parbery-Clark et al measured speech-evoked auditory brainstem responses (ABRs) of musicians and non-musicians via scalp electrodes. The electrode signals were analyzed to measure neural response amplitude and neural timing. The hypothesis was that musicians would have faster neural timing and increased amplitudes of response peaks (i.e. that they process quicker, and the magnitude of neural response would be greater). Musician groups included anyone who had consistently practiced an instrument at least 3 times a week since 7 years of age. Non-musician groups included subjects that had less than 3 years of musical training at any point in their lifetime. In total, this study included 30 participants with 15 musicians and 15 non-musicians. The auditory component of the ABRs was a 40ms speech syllable, /da/, which was presented either monaurally on the left or right side, or diotically, via inserted headphones.

 For the assessment of speech-in-noise, this group used the "Hearing in Noise Test" from Biologic Systems. Here, the participants were asked to repeat 20 short sentences that were heard with acoustically fixed background noise from a loudspeaker. The performance was assessed based on the minimal intensity of the target sentence, relative to the background noise, at which the participant could correctly repeat at least 50% of the target sentences.

 The results demonstrate that musicians exhibit faster neural timing and more consistent responses when presented with diotic ques, but musicians and non-musicians performed equally well monoaurally. Musicians also had better speech-in-noise performance. Intriguingly, musicians and non-musicians both exhibited faster neural timing peaks after diotic ques, but this difference was more drastic in the musician group. Across all subjects, faster neural response and greater magnitude of that response after diotic stimuli, were directly correlated with better speech-in-noise perception.

 These results support the use of music training in treatment of compromised binaural processing. Also, the average elementary school classroom has a decibel level of approximately 60. A normal conversation would generally take place at 50 decibels. This noise level creates obvious barriers to learning; however, music training would enhance a child's speech-in-noise perception and would thereby improve their learning experience.


Response:

 I thoroughly enjoyed this paper. I feel the authors had a meticulous experimental plan, which used three distinct controls. These included an initial test with all subjects measuring neural timing response to a 100 microsecond click stimulus- which tests their general neural response and ensures that they were all within a normal range, irrespective of musical training- a 35 microvolt signal boundary that differentiates between true signal and artifacts, and randomized application of diotic and monaural conditions across the subjects to rule out contributions due to neural fatigue and adaptation between environments.

 The authors also mentioned that other experiments had conversely found an increase in monaural processing in musicians; however, the authors suggest that because the syllable cue used did not contain the acoustically rich vowel portion, this removed the advantage. This decision was based on previous studies that link the acoustically rich vowel portion of a syllable with musicians' enhanced neural encoding of the spectral components in speech. These results indicate that this was indeed the case, and this further illustrates the depth, and thoroughness with which Parbery-Clark et al approached their experimental design.

 I have a very limited understanding of ABR, but from the information provided in this paper, this method of measuring neural response seems robust and reliable. These results indicate a statistically significant correlation between enhanced diotic auditory processing and speech-in-noise perception, and more importantly, this scientifically proves a measurable increase in cognitive performance based on musical training. Music training does apparently make you smarter!

 The only critique I can offer for this paper is that in the discussion, the correlation between music training and increased speech-in-noise perception was proposed to be a result of ensemble playing or conducting. This suggests that the speech-in-noise perception enhancement would not result from private lessons or individual practice, which is in direct contrast with their concluding statement that music lessons in general would illicit these benefits (Practical Applications section). Also, just because the diotic processing and speech-in-noise perception were correlated, does not mean that diotic processing is solely responsible for this benefit. I think this study proves that they are both increased due to music training, and perhaps this enhancement is due to increased diotic processing, but there may be a large assortment of factors that contribute to this,that are equally enhanced with music training, such as: acoustically rich vowel recognition, or non-diotic binaural processing.

 Overall, I found this study to be thorough, informative, and scientifically satisfying. I would be intrigued to see if the speech-in-noise perception increase varies with soloist musicians vs. ensemble players, but every study must leave something for the next person :).






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