Hearing scientist and statistician.
I study how the two ears work together to figure out where sounds are located and understand speech in background noise. These make up binaural or spatial hearing. It is easy for people with typically developed hearing to take this for granted. However, much research shows that there are benefits of providing access to sound in both ears for people who experience hearing loss (see this paper for a review of clinical guidelines). For this reason, providing hearing to both ears is becoming the standard of care in audiology.
I have been working with people who experience hearing loss to study the benefits and limitations of spatial hearing since 2013. My undergraduate and doctoral research focused on patients who have cochlear implants, and my post-doctoral research focuses on hearing loss that is difficult to diagnose using traditional techniques. The purpose of this page is to give a small overview of what we think happens for people who experience hearing loss that interferes with their ability to gain the benefits of spatial hearing. My mentors, peers, mentees, and I have worked with this framework to come up with solutions for how to improve outcomes for patients by advancing means of clinical assessment and improving hearing devices.
Sound source localization is the process by which people identify where sounds are located around them. The classic way to study this is to present sounds from speakers around someone’s head and ask them where the sound came from. Alternatively, researchers can manipulate sounds presented over headphones to provide cues suggesting that the sound was presented from a particular location (called “virtual acoustic space”). My and others’ research has shown the following patterns related to patients who experience hearing loss compared to age-matched, typically hearing peers:
If we think of the auditory system as applying a spotlight-like filter to the environment, then accurate localization performance occurs when the the spotlight is narrow (shown on the left below). On the other hand, when localization is poor, the spotlight is wide, resulting in more frequent and greater errors (shown on the right below).
The questions many of us try to answer are: Why? What factors contribute to poorer performance and how do we diagnose and address them? In contrast to a lot of other neuroscience research, the auditory system has some well-defined neural circuits that seem to be involved with locating sounds. My research has focused on one particular circuit, the lateral superior olive.
The lateral superior olive sits near the middle of the brainstem and responds to changes in the location (left vs. right) of high-frequency and short sounds. Specifically, the lateral superior olive seems to respond to the difference between the time of arrival and intensity of the sound in each ear. These are referred to as interaural time differences (ITDs) and interaural level differences (ILDs). I have studied the lateral superior olive by modeling its responses to different kinds of sounds during graduate school, and will be measuring the auditory brainstem responses of humans and other animals in my post-doc.
Sound source segregation is the process by which the auditory system separates one sound from another. Because this is so general, there is no “classic” way to address this problem. Different researchers have used sounds as simple as sine tones or as complicated as mixtures of speech. My and others’ research has shown the following patterns for patients who experience hearing loss compared to age-matched, typically hearing peers:
Instead of hearing two sounds as separate and coming from different locations (shown on the left below), it is suspected that listeners with hearing loss may fail to segregate sounds and instead link them together (“fuse” them; shown on the right below). This makes it more difficult to determine additional information about a sound (e.g., what word was spoken).
For the most part, studies have focused on sound source segregation or the percentage of correctly understood words, not both. Only recently have studies begun addressing both simultaneously.
Researchers have developed an extensive understanding of how spatial hearing works in the typically developed auditory system using many creative approaches. This is a difficult problem and efforts have taken place over centuries. More recently, the focus has shifted to improving the lives of patients who experience hearing loss. Accordingly, many new factors need to be considered, like:
One factor that I have explored in my research is differences between the ears within the same patient. In other fields, like cognitive science for example, it is taken as a given that one side of the brain may be more efficient at processing certain kinds of information. Spatial hearing research on the other hand usually assumes that the ears of individuals are similar to one another. However, there is increasing evidence that patients who experience hearing loss tend to have a “better ear” (e.g., better hearing thresholds or speech understanding), and this is not considered in most clinical interventions. In fact, hearing devices may introduce greater differences between the ears, leading to poorer outcomes.
In my and others’ work, a few consistent trends have been found:
This research is still very new, and much needs to be done to determine how to use this new information to help patients. Because restoring hearing in both ears is associated with better outcomes than restoring hearing in only one ear, our focus has mainly been to determine how to promote the best spatial hearing outcomes and identify how to prevent major differences between the ears from developing for patients. Some promising results show that training patients to localize sounds or understand speech, giving a person access to hearing as early as possible, and matching devices across ears lead to better outcomes.
I plan to continue to dedicate myself to studying and addressing differences in hearing outcomes between the ears as long as I am doing hearing research. I hope to work with people who may be especially at risk of experiencing asymmetric hearing loss and collaborate on realistic and effective interventions. I plan to use my position and power to contribute to the advancement of students and researchers who are traditionally underrepresented in hearing science, including but not limited to Black, Indigenous, and all other people of color; people who identify as transgender or cis-gender female; people with disabilities, including hearing loss; members of the LGBTQ+ community; economically disadvantaged and first-generation students.
If you would like to read an extensive collection of my original research, my doctoral dissertation is available for free online from the University of Wisconsin-Madison. Each chapter is currently being prepared and submitted for publication in academic journals.
If you would like to read a copy of one of these publications and are unable to attain access it, please reach out to me via the Contact form on this website and I would be happy to provide it to you.
Anderson, S. R., Gallun, F. J., & Litovsky, R. Y. (2023). Interaural asymmetry of dyanic range: Abnormal fusion, bilateral interference, and shifts in attention. Front Neurosci, 16, 1018190.
Anderson, S. R., Kan, A., & Litovsky, R. Y. (2022). Asymmetric temporal envelope sensitivity: Within- and across-ear envelope comparisons in listeners with bilateral cochlear implants. J Acoust Soc Am, 152(6), 3294-3312.
Uhler, K., Anderson, S. R., Yoshinaga-Itano, C., Walker, K. A., & Hunter, S. (2022). Speech discrimination in infancy predicts language outcomes at 30 months for both children with normal hearing and those with hearing differences. J Clin Med, 11(19), 5821.
Anderson, S. R., Jocewicz, R., Kan, A., Zhu, J., Tzeng, S., & Litovsky, R. Y. (2022). Sound source localization patterns with bilateral cochlear implants: Age at onset of deafness effects. PLoS ONE, 17(2), e0263516.
Anderson, S. R., Glickman, B., Oh, Y., & Reiss, L. A. J. (2020). Binaural pitch fusion: Effects of sound level in normal-hearing listeners. Hear Res, 396, 108076.
Thakkar, T., Anderson, S. R., Kan, A., & Litovsky, R. Y. (2020). Evaluating the impact of age, acoustic exposure, and electrical stimulation on binaural sensitivity in bilateral cochlear implant patients. Brain Sci, 10(6), 406.
Anderson, S. R., Easter, K., & Goupell, M. J. (2019). Binaural temporal processing in aging cochlear-implant and normal-hearing listeners. J Acoust Soc Am, 146(5), 3232-3254.
Anderson, S. R., Kan, A., & Litovsky, R. Y. (2019). Asymmetric temporal envelope encoding: Implications for within- and across-ear envelope comparison. J Acoust Soc Am,146(2), 1189-1206.
Brown, B. P., Kang, S., Gawelek, K., Zacharias, R., Anderson, S. R., Turner, C., & Morris, J. K. (2014). In vivo and in vitro ketamine exposure exhibits a dose-dependent induction of activity-dependent neuroprotective protein in rat neurons. Neuroscience, 290, 31-40.
Anderson, S. R. (2020). Mechanisms that underlie poorer binaural outcomes in patients with asymmetrical hearing and bilateral cochlear implants. National Institute on Deafness and Other Communication Disorders, F31 DC018483-01A1.