Our ears are open all the time. Even sleeping newborn infants subconsciously respond to the sounds around them, indicating that from birth (1), humans are constantly exposed to their auditory environment.
In their review of the research evidence, Kraus & Chandrasekaran, (2) underlined the importance of the initial, subconscious (subcortical) stage of auditory processing. Before sound reaches our attention, the auditory brainstem responds to incoming information from our ears, integrating the spatial, rhythmical and acoustical features of sounds.
These features include frequency (high and low pitches), the timbre of the sound (for example, differentiating between human voices) and rhythmic features (such as the regularity or predictability of sounds). The auditory brainstem is extremely sensitive to very subtle differences in sound waves, such as individual phonemes in language and plays a critical role in early identification of sounds and their patterns in particular. Over time, the auditory brainstem produces an idiosyncratic response to sound that is unique to each individual.
Thus, the auditory brainstem response reflects the current state of the nervous system – the state at that time formed by an individual’s life experience with sound (ibid, 2010, pp. 601).
More recently, researchers have found that the auditory brainstem seems to respond with greatest clarity to the sounds with which the individual is most familiar. Having listened to brainstem responses of musicians, they found that for example, pianists’ brainstem responses to the sounds produced by a piano were unusually sharply defined when compared to those of non-pianists. Brainstem responses also appeared to receive feedback information from cortical areas of the brain (3).
Further developing the line of enquiry, scholars (4) proposed that the availability of cortical feedback (from the cognitive processing of sound) allowed the brainstem response to become increasingly specific over time. For instance, musical expertise that has accumulated over a lifetime leads to extremely fine-grained auditory brainstem responses among professional musicians, not only to musical sounds, but also both to phonemes and the pitch contours of language (5). Once the brainstem has adapted to cortical feedback, it appears to retain its enhanced structures as confirmed by a recent study of speakers of Mandarin and amateur musicians (6).
Overall these studies show that an overlap exists between early stage auditory processing of spoken language and musical experiences. Cognitive feedback informs development of these structures and expertise in music appears to enhance the auditory brainstem response to language, which coincides with our work in Rhythm for Reading.
1. Nameth, R., Haden, G., Miklos, T. & Winkler, I (2015) Processing of horizontal sound localization cues in newborn infants, Ear and Hearing, 36 (5), pp. 550-556
2. Kraus, N and Chandrasekaran, B. (2010) Music training for the development of auditory skills, Nature Neuroscience, 11, pp. 599-605
3. Strait, D.L. Chan, K., Ashley, R., & Kraus, N (2010) Specialisation among the specialised: Auditory brainstem function is tuned to timbre, Cortex, 48, pp. 360-362
4. Skoe, E., Krizman, J., Spitzer, E., & Kraus, N. (2014) Prior experiences biases subcortical sensitivity to sound patterns, Journal of Cognitive Neuroscience, 27 (1), pp.124-140
5. Musacchia, G., Sams, M., Skoe, E. & Kraus, N. (2007) Musicians have enhanced subcortical auditory and audiovisual processing of speech and music. Proc. Natl Acad. Sci. USA 104.
6. Bidelman, G.M., Gandour, J.T., Krishnan, A., (2011). Cross-domain effects of music and language experience on the representation of pitch in the human auditory brainstem. J. Cogn. Neurosci. 23, 425–434.