Auditory Neuroscience: Exploring the Science of Hearing
Auditory neuroscience is a fascinating field that delves into the complexities of how we perceive sound. It explores everything from the development of the inner ear to the intricate neural computations that allow us to understand speech and locate sound sources. This article reviews recent progress in auditory research and seeks to elicit contemporary answers to fundamental questions about hearing.
One of the central questions in auditory neuroscience is: how does the complex inner ear develop? The inner ear begins as a simple placode of the embryo. The cells then undergo a series of steps to form six receptor organs, including the ellipsoidal utricle and saccule, and the snail-like cochlea. The constituent cells meanwhile begin to adopt several fates, forming an array of hair cells separated by supporting cells. These processes involve complex manipulations of the cytoskeleton.
Another critical question is: how does the inner ear transduce sounds into electrical signals? The process rests on three fundamental insights. The properties of the basilar membrane, such as its mass and tension, determine how different frequencies are represented along the basilar membrane. This frequency discrimination is a topic of lively debate. Active movements of the mechanoreceptive hair bundles also play a crucial role. Additionally, the structure's responsiveness is highly nonlinear; amplification is negligible for loud sounds.
Cross-section of the cochlea, highlighting its structure and function in auditory transduction.
The auditory system is built for speed. The time required by auditory neurons is significantly less than the milliseconds required by photoreceptors and olfactory neurons. Some auditory neurons can fire action potentials at rates approaching 1,000 per second. This rapid response shortens the climb to threshold.
Sound Localization
How do we compute the location of a sound source? The localization of sound sources in space is crucial for survival, prompting us to turn our eyes or head for closer inspection. This procedure involves remarkable neural computations to determine a source's position. The brain can detect interaural time differences with a precision of approximately 0.1%, an interval comparable to the duration of a single action potential. Our ability to distinguish different elevations depends on their frequencies, creating a visual-auditory map similar to how we perceive visual objects.
Diagram illustrating how the brain uses interaural time and intensity differences to localize sound sources.
Speech Perception
The perception of complex sounds, particularly speech, is another area of intense research. Understanding how we interpret the complex sonic signals that constitute speech, and the extensive lexicon of primates, has been a challenge. The complexity of the region has been appreciated only recently, even after 50 years' effort!
Here's a table summarizing key aspects of auditory processing:
| Aspect | Description |
|---|---|
| Inner Ear Development | Formation of receptor organs (utricle, saccule, cochlea) from the embryonic placode. |
| Sound Transduction | Conversion of sound waves into electrical signals via hair cells and the basilar membrane. |
| Frequency Discrimination | Representation of different frequencies along the basilar membrane. |
| Speed of Processing | Auditory neurons can fire action potentials at rates up to 1,000 per second. |
| Sound Localization | Computation of sound source location using interaural time and intensity differences. |
| Speech Perception | Interpretation of complex sonic signals and the extensive lexicon. |
Many people in industrialized countries suffers from significant hearing loss. Understanding how hair cells develop will suggest a means of regenerating them. There are reasons to hope for success in this endeavor. In nonmammalian vertebrates, such as amphibians, hair cells are formed throughout life by this means, offering hope for treatments that can restore hearing lost due to aging, noise exposure, or ototoxic drugs.
Recent Publications:
- Xu, C., Cheng, F. Y., Medina, S., Eng, E., Gifford, R., & Smith, S.B. (2023). Frequency following responses to simulated bimodal speech: Acoustic bandwidth effects. Proceedings of the Meeting on Acoustics.
- Eng, E., Xu, C., Medina, S., Cheng, F. Y., Gifford, R., & Smith, S.B. (2022).
- Smith, S.B. (2022). Translational applications of Machine Learning in Auditory Electrophysiology. In Seminars in Hearing 43(03), 240-250.
- Cone, B. K., Smith, S.B., & Smith, D. E. C. (2022).
- Cheng, F. Y. & Smith, S.B. (2022). Objective detection of the speech frequency following response (sFFR).
- Cheng, F. Y., Xu, C., Gold, L., & Smith, S.B. (2021).
- Xu, C., Cheng, F. Y., Medina, S., & Smith, S.B. (2021).
- Cheng, F. Y., Xu, C., Goodall, H., Ornelas, M. E., Gold, L., & Smith, S.B. (2021).
- Thompson, E.C., Estabrook, R., Krizman, J., Smith, S.B., Huang, S., White-Schwoch, T., Nicol, T., & Kraus, N. (2021).
- Madrid, A. M., Walker, K. A., Smith, S. B., Hood, L. J., & Prieve, B. A. (2021).
- Smith, S. B., & Cone, B. (2021).
- Kornguth, S., Rylander, H. G., Smith, S., Campbell, J., Steffensen, S., Arnold, D., ... & Rutledge, J. N. (2021).
- So, W., & Smith, S. B. (2020).
- Kessler, D. M., Ananthakrishnan, S., Smith, S. B., D’Onofrio, K., & Gifford, R. H. (2020).
- D’Onofrio, K.L., Limb, C., Caldwell, M., Smith, S.B., Kessler, D.M., Gifford, R.H.
- Smith, S., & So, W. (2019).
- D'Onofrio, K., Smith, S.B., Kessler, D., Williams, G., & Gifford, R. (2019).
- Burrick, H., Suneel, D., Chole, R., Buchman, C., Smith, S.B., Lee, C., Hancock, K.E., Long, G.R., Dhar, S., Ortmann, A.J., Ward, B.K., Lichtenhan, J.T. (2019). On the origins of physiologic modulation of a low-noise microphone in a human ear canal. In Valente, M. & Valente, M. (2nd Ed.) Adult Audiology Casebook.
- Smith, S.B., Krizman, J., Liu, C., White-Schwoch, T., Nicol, T., & Kraus, N. (2019).
- Kraus, N. & Smith, S.B.
- Smith, S. B., Ichiba, K., Velenovsky, D. S., & Cone, B. (2017).
- Smith, S.B., Lichtenhan, J. T., & Cone, B. K. (2017).
- Filippini, R., Smith, S.B., & Musiek, F. E. (2017).
- Cone, B., Smith, S.B., & Cheek, D. (2017).
- Smith, S.B., Lichtenhan, J., & Cone, B. (2016).
- Smith, S.B. & Cone, B.K. (2015).
- Smith, S.B. & Musiek, F.
- Smith, S.B. & Musiek, F.