Dynamic Sound Processing and the Inner Ear: An Inside Look at the Charaziak Lab

Dr. Karolina Charaziak (PhD) always dreamed of becoming a professor, and she eventually fell in love with hearing science because of the way that it combined physics and mathematics with biology and healthcare. Dr. Charaziak grew up in Poland, her father a plumber, her mother a librarian. She earned her BS in Hearing Care and Noise Control and her MS in Acoustics (equivalent to an MS in Audiology in the United States), but as she began to see patients as a clinician, she found that these interactions created more questions than answers. For example, why was it that if two patients with similar hearing loss were given the same hearing aids, one might be thrilled, wearing the hearing aids every day, while the other may throw the hearing aids in a drawer out of frustration or disappointment and never return to her office again?

As a result of her time as an audiologist, Dr. Charaziak became interested in developing better diagnostics for hearing loss, completing a PhD in Communication Sciences and Disorders at Northwestern University, working with Dr. Jonathan Siegel (PhD) on trying to find more objective ways to learn about human frequency selectivity. Still, though, she kept asking basic questions that did not have answers as she bumped up against the limitations of human research. “Even now, we don’t really know the etiology of hearing loss in humans,” Dr. Charaziak explained. “Working with humans, we are only able to indirectly verify what’s happening in the inner ear.” She realized that by turning to basic scientific research on animals, she could focus on using invasive measurements of inner ear responses that she could then potentially use to guide best practices in human research.

In her laboratory, Dr. Charaziak studies how the cochlea of the inner ear processes sounds utilizing both direct measurement of cochlear responses (from, for instance, intracochlear vibrometry) and indirect measurement of cochlear responses (from, for instance, otoacoustic emissions) in combination with theoretical modeling. More specifically, her lab is pursuing two main lines of research that are complementary but focus on different primary questions. In the longer-term, Dr. Charaziak is pursuing research exploring how the inner ear deals with processing dynamic and/or complex sounds. “We all agree that we live in an acoustically complex environment,” she noted. “Somehow, our ear needs to be able to encode all of this.” In the past, scientists studied inner ear processing with simple sounds like tones and clicks. This could provide insights that were relevant in a laboratory setting, but said insights were not necessarily applicable in the real world. Dr. Charaziak instead developed a project in which sounds are modified on a gradual scale, using sounds that resemble chirps. Because it is easy to manipulate the acoustical properties of these sounds, making them dynamic, it allows researchers to learn more about dynamic processing in the inner ear. Previous studies in humans have shown that when a sound increases or decreases in pitch, it can make a huge difference in how we hear it, but there is still much to be learned about how sounds get encoded at the periphery of our hearing as well as how hearing one sound may affect how we perceive another sound and how our processing of dynamic sounds may change over time.

In conjunction with her research on the inner ear’s susceptibility to the dynamics of sound, Dr. Charaziak is also looking at how different objective measures like cochlear microphonics and otoacoustic emissions could help us to determine the etiology of sensory hearing loss using noninvasive techniques. She plans to start with mice, inducing different types of sensory hearing loss, and while these different types of hearing loss may all look the same on an audiogram, she hopes that eventually, her research will help scientists develop diagnostic tools that will allow us to detect the etiology of a person’s sensory hearing loss, leading to more individualized treatment plans.

Dr. Charaziak’s favorite part about having her own lab is being able to apply for funding on the grounds of her own ideas, pursuing exactly what it is that she wants to pursue. She notes that one of the greatest challenges is that those who run labs are usually trained as scientists, not managers, and it can be difficult to figure out and keep up with all of the required paperwork, including maintaining inventories, making sure that all human and animal protocols are up-to-date, hiring and training staff, and keeping track of expenses. She is grateful to the various mentors who have helped to lead the way for her, including Dr. Mario Ruggiero (PhD), who was part of her PhD committee and helped Dr. Charaziak to become more open to receiving criticism as a crucial tool in improving one’s ideas; Dr. Jonathan Siegel (PhD), her PhD advisor, who encouraged her to always work on something she was passionate about; and Dr. Christopher Shera (PhD), her mentor and colleague at USC, who has always given her an incredible amount of freedom as a researcher. Dr. Charaziak recognizes, however, that there are still very few female researchers in the field, and she is actively working toward helping to recruit more diverse talent. As one of the co-organizers of the 2024 Mechanics of Hearing Workshop at the University of Michigan, for example, she sought to encourage participation from various underrepresented groups in otolaryngology and audiology, and she hopes that the next generation of auditory researchers will represent a greater range of different backgrounds and perspectives, which she cites as essential to the sort of out-of-the-box thinking that leads to the most exciting and innovative new ideas. In terms of advice to those entering the field, Dr. Charaziak says, “We should normalize the idea of ‘imposter syndrome.’ A good scientist questions everything. If you’re too certain, you may be missing important insights, questions, and observations.”