AUDITORY NEUROSCIENCE RESEARCH
My passion for understanding auditory perception and the brain has led me to pursue a Doctor of Philosophy in neuroscience. I am currently enrolled in the Neuroscience Graduate Program at Vanderbilt University. My primary advisor is Ramnarayan Ramachandran. We investigate the consequences of hearing loss on the central auditory system using macaque monkeys as an animal model. We utilize a variety of methods, including behavioral psychoacoustics, single-unit neurophysiology, and objective clinical audiology techniques such as auditory brainstem response (ABR) and otoacoustic emissions (DPOAE) testing.
I am relentless in my pursuit of research, while remaining loyal to my clinical training and experiences with patients. My clinical training provides me the practical, translational foundation in which I place so much value, while giving my research meaning beyond that of pure scientific curiosity.
Burton, J. A., Mackey, C. A., MacDonald, K. S., Hackett, T. A., & Ramachandran, R.
(2020). Hearing Research
Exposure to loud noise causes damage to the inner ear, including but not limited to outer and inner hair cells (OHCs and IHCs) and IHC ribbon synapses. This cochlear damage impairs auditory processing and increases audiometric thresholds (noise-induced hearing loss, NIHL). However, the exact relationship between the perceptual consequences of NIHL and its underlying cochlear pathology are poorly understood. This study used a nonhuman primate model of NIHL to relate changes in frequency selectivity and audiometric thresholds to indices of cochlear histopathology. Three macaques (one Macaca mulatta and two Macaca radiata) were trained to detect tones in quiet and in noises that were spectrally notched around the tone frequency. Audiograms were derived from tone thresholds in quiet; perceptual auditory filters were derived from tone thresholds in notched-noise maskers using the rounded-exponential fit. Data were obtained before and after a four-hour exposure to a 50-Hz noise centered at 2 kHz at 141 or 146 dB SPL. Noise exposure caused permanent audiometric threshold shifts and broadening of auditory filters at and above 2 kHz, with greater changes observed for the 146-dB-exposed monkeys. The normalized bandwidth of the perceptual auditory filters was strongly correlated with audiometric threshold at each tone frequency. While changes in audiometric threshold and perceptual auditory filter widths were primarily determined by the extent of OHC survival, additional variability was explained by including interactions among OHC, IHC, and ribbon synapse survival. This is the first study to provide within-subject comparisons of auditory filter bandwidths in an animal model of NIHL and correlate these NIHL-related perceptual changes with cochlear histopathology. These results expand the foundations for ongoing investigations of the neural correlates of NIHL-related perceptual changes.
Burton, J. A., Valero, M. D., Hackett, T. A., & Ramachandran, R.
(2019). Journal of the Acoustic Society of America.
Exposure to prolonged or high intensity noise increases the risk for permanent hearing impairment. Over several decades, researchers characterized the nature of harmful noise exposures and worked to establish guidelines for effective protection. Recent laboratory studies, primarily conducted in rodent models, indicate that the auditory system may be more vulnerable to noise-induced hearing loss (NIHL) than previously thought, driving renewed inquiries into the harmful effects of noise in humans. To bridge the translational gaps between rodents and humans, nonhuman primates (NHPs) may serve as key animal models. The phylogenetic proximity of NHPs to humans underlies tremendous similarity in many features of the auditory system (genomic, anatomical, physiological, behavioral), all of which are important considerations in the assessment and treatment of NIHL. This review summarizes the literature pertaining to NHPs as models of hearing and noise-induced hearing loss, discusses factors relevant to the translation of diagnostics and therapeutics from animals to humans, and concludes with some of the practical considerations involved in conducting NHP research.
Holcomb, M. A., Burton, J. A., Dornhoffer, J. R., Camposeo, E. L., Meyer, T. A., & McRackan, T. R. (2019). Laryngoscope.
Objective: To determine indications, surgical efficacy, and audiologic outcomes of replacing Advanced Bionics Clarion C1.2 internal devices (Advanced Bionics, LLC, Valencia, CA) as a means of technology upgrade.
Study Design: Retrospective review, case series.
Methods: Ten patients were initially implanted as a child (mean age = 3.87 years) and underwent cochlear implant reimplantation (CIR) with current Advanced Bionics internal device as a young adult (mean duration of implant use = 15.66 years). Demographic data and pre‐ and post‐CIR speech perception scores were collected.
Results: Technology upgrade was the primary (9) or secondary (1) motivation for CIR. No surgical complications were noted, and full insertion was obtained in nine cases. Intraoperative impedance levels and neural response imaging measures were within normal limits for eight patients. At most recent post‐CIR follow‐up evaluation, all patients (100%) performed within or better than the 95% confidence interval of their pre‐CIR word and sentence recognition scores; and 55.6%, 50.0%, and 50.0% of patients performed above the 95% confidence interval of their pre‐CIR scores for the CNC words, sentences in quiet, and sentences in noise, respectively.
Conclusion: Post‐CIR audiological benefit was stable or improved compared to pre‐CIR results in all categories by 3 months after reactivation. Given these results, patients who are unable to use the most current external processors due to incompatibility with a legacy internal device could consider reimplanation to optimize their overall performance with a cochlear implant.
Rajsic, J., Burton, J. A., & Woodman, G. F. (2019). Psychophysiology.
Electrophysiological studies have demonstrated that the maintenance of items in visual working memory (VWM) is indexed by the contralateral delay activity (CDA), which increases in amplitude as the number of objects to remember increases, plateauing at VWM capacity. Previous work has primarily utilized simple visual items, such as colored squares or picture stimuli. Despite the frequent use of verbal stimuli in seminal investigations of visual attention and memory, it is unknown whether temporary storage of letters and words also elicit a typical load‐sensitive CDA. Given their close associations with language and phonological codes, it is possible that participants store these stimuli phonologically, and not visually. Participants completed a standard visual change‐detection task while their ERPs were recorded. Experiment 1 compared the CDA elicited by colored squares compared to uppercase consonants, and Experiment 2 compared the CDA elicited by words compared to colored bars. Behavioral accuracy of change detection decreased with increasing set size for colored squares, letters, and words. We found that a capacity‐limited CDA was present for colored squares, letters, and word arrays, suggesting that the visual codes for letters and words were maintained in VWM, despite the potential for transfer to verbal working memory. These results suggest that, despite their verbal associations, letters and words elicit the electrophysiological marker of VWM encoding and storage.
McRackan, T. R., Fabie, J. E., Burton, J. A., Munawar, S., Holcomb, M. A., & Dubno, J. R.
(2018). Otology & Neurotology.
Objective: Compare word recognition scores for adults undergoing cochlear implant evaluations (CIE) measured using earphones and hearing aids. Study Design: Retrospective review of data obtained during adult CIEs. Patients: Two hundred eight ears in 183 subjects with greater than 10% word recognition scores measured with earphones. Interventions/Main Outcomes Measured: Preoperative pure-tone thresholds and word recognition scores measured with earphones and hearing aids. Results: A review of audiological data obtained from 2012 to 2017 during adult CIEs was conducted. Overall, a weak positive correlation (r = 0.33, 95% confidence interval 0.17 – 0.40, p < 0.001) was observed between word recognition scores measured with earphones and hearing aids. Earphone to aided differences (EAD) ranged from -38 to +72% (mean 14.3 +/- 19.9%). Consistent with EADs, 108 ears (51.9%) had earphone scores that were significantly higher than aided word recognition scores (+EAD), as determined by 95% confidence intervals; for 14 ears (6.7%), earphone scores were significantly lower than aided scores (-EAD). Moreover, of the patients with earphone word recognition scores >/= 50%, 82.6% were CI candidates based on aided AzBio+10 dB SNR scores. Conclusion: These results demonstrate the limited diagnostic value of word recognition scores measured under earphones for patients undergoing CIE. Nevertheless, aided word recognition is rarely measured before CIEs, which limits the information available to determine CI candidacy and referral for CIEs. Earlier and routine measurement of aided word recognition may help guide clinical decision making by determining the extent to which patients are achieving maximum benefit with their hearing aids or should consider cochlear implantation.
Burton, J. A., Dylla, M. E., & Ramachandran, R. (2018). Hearing Research.
Frequency selectivity as estimated by auditory filters has been well quantified in humans and other mammalian species using behavioral and physiological methodologies, but little work has been done to examine frequency selectivity in nonhuman primates. The purpose of this study was to investigate the frequency selectivity of macaque monkeys using a notched-noise paradigm. Macaque auditory filters were symmetric at low noise levels and broader and more asymmetric at higher noise levels. Macaque filters were broader than human filters. These data serve as a baseline for ongoing studies of neuronal frequency selectivity and frequency selectivity in subjects with hearing loss.
Hauser, S. N., Burton, J. A., Mercer, E. T., & Ramachandran, R. (2018). Hearing Research.
This report explores the consequences of acoustic overexposures on hearing in noisy environments for macaque monkeys. Behavioral and physiological assessments were obtained before and after noise exposure. Physiological measurements showed elevated auditory brainstem response (ABR) thresholds and absent distortion product otoacoustic emissions (DPOAEs) post-exposure. Behavioral measures revealed frequency specific increases in tone detection thresholds, lower threshold shift rates, and minimal release from masking with sinusoidally amplitude modulated (SAM) noise. These results reveal that behavioral and physiological effects of noise exposure in macaques are similar to those seen in humans and provide preliminary information on the relationship between noise exposure, cochlear pathology, and perceptual changes in hearing within individual subjects.
Valero, M. D., Burton, J. A., Hauser, S. N., Hackett, T. A., Ramachandran, R., & Liberman, M. C. (2017). Hearing Research.
Cochlear synaptopathy can result from various insults, including acoustic trauma, aging, ototoxicity, or chronic conductive hearing loss. For example, moderate noise exposure in mice can destroy up to ∼50% of synapses between auditory nerve fibers (ANFs) and inner hair cells (IHCs) without affecting outer hair cells (OHCs) or thresholds, because the synaptopathy occurs first in high-threshold ANFs. However, the fiber loss likely impairs temporal processing and hearing-in-noise, a classic complaint of those with sensorineural hearing loss. Non-human primates appear to be less vulnerable to noise-induced hair-cell loss than rodents, but their susceptibility to synaptopathy has not been studied. Because establishing a non-human primate model may be important in the development of diagnostics and therapeutics, we examined cochlear innervation and the damaging effects of acoustic overexposure in young adult rhesus macaques. Anesthetized animals were exposed bilaterally to narrow-band noise centered at 2 kHz at various sound-pressure levels for 4 h. Cochlear function was assayed for up to 8 weeks following exposure via auditory brainstem responses (ABRs) and otoacoustic emissions (OAEs). A moderate loss of synaptic connections (mean of 12-27% in the basal half of the cochlea) followed temporary threshold shifts (TTS), despite minimal hair-cell loss. A dramatic loss of synapses (mean of 50-75% in the basal half of the cochlea) was seen on IHCs surviving noise exposures that produced permanent threshold shifts (PTS) and widespread hair-cell loss. Higher noise levels were required to produce PTS in macaques compared to rodents, suggesting that primates are less vulnerable to hair-cell loss. However, the phenomenon of noise-induced cochlear synaptopathy in primates is similar to that seen in rodents.
LINKING PERCEPTUAL PERFORMANCE WITH COCHLEAR HISTOPATHOLOGY IN TWO NONHUMAN PRIMATE MODELS OF NOISE-INDUCED HEARING LOSS
West Lafayette, IN
March 5, 2020
In order to directly examine the relationship between cochlear pathology and perceptual deficits, we employed a comprehensive behavioral test battery that probed hearing sensitivity and spectral, temporal, and spatial processing in our macaque models of noise-induced sensorineural hearing loss (SNHL) and noise-induced synaptopathy (SYN). We identified distinct patterns of perceptual deficits that differentially predicted the type (SNHL vs. SYN), frequency range, and, to some extent, the severity of noise-induced cochlear pathology. These findings provide an essential and direct link between cochlear pathophysiology and the perceptual consequences of hearing loss, elevating the specificity of clinical diagnostics as a foundation for forthcoming therapeutic treatment options.
VISION & HEARING: FROM MOLECULES TO SENSORY LOSS
Osher Lifelong Learning Series
October 22, 2019
This lecture, presented in collaboration with Sarah Naguib, was part of the neuroscience course offering for the Osher Lifelong Learning Series presented by Vanderbilt University. We discussed the visual system, the auditory system, sensory processing in the brain, mechanisms of peripheral vision and hearing loss, and the neural consequences of sensory deprivation.
NEUROSCIENCE AND AUDIOLOGY
October 16, 2019
Invited guest lecture presentation for the Miami University of Ohio National Student Speech Language Hearing Association Chapter
HEARING IN BACKGROUND NOISE IN MACAQUE MONKEYS FOLLOWING NOISE EXPOSURE
Midwest Auditory Research Conference
Hearing loss causes perceptual deficits in the time and frequency domains, resulting in difficulty hearing in background noise. However, these deficits are quite variable among individuals, even those with similar clinical audiometrics. Some of this variability may be due to differences in underlying cochlear pathology, specifically the loss of inner and outer hair cells and ribbon synapses. Identifying behavioral assays sensitive to these differences will improve clinical diagnostics and treatment. In order to directly examine the relationship between cochlear pathology and perceptual deficits, we characterized masked tone detection in our macaque models of noise-induced hearing loss (NIHL).
HOT TOPICS, COLD DRINKS: UNCONVENTIONAL AUDIOLOGY
American Academy of Audiology
AAA 2019 Conference Columbus, OH
March 29, 2019
This session featured audiologists who work in uncommon environments, exploring the versatility and wide array of applications that audiology can have including an animal research audiologist, a forensic audiologist, and a NASA audiologist.
NEURONAL FREQUENCY SELECTIVITY IN THE INFERIOR COLLICULUS AND COCHLEAR NUCLEUS OF THE AWAKE BEHAVING MACAQUE MONKEY
Acoustical Society of America
Victoria, BC, Canada
November 8, 2018
Frequency selectivity relates to the ability to process complex signals and can be measured through auditory filters. Behavioral filters show broader tuning compared to cochlear and auditory nerve fiber tuning. To test whether filters evolve across the auditory pathway or if they are established in the periphery, we estimated neural filters in the cochlear nucleus (CN) and inferior colliculus (IC) and compared with simultaneously measured behavioral filters in macaques. Three macaques were trained to detect tones (signal = unit characteristic frequency (CF)) in spectrally notched maskers of varying width while single unit responses were recorded in the CN and IC. Filter shapes and bandwidths were estimated from the masked thresholds using the rounded exponential fit. Behavioral and neural filters increased in bandwidth with increasing CF. Behavioral and neural bandwidths were significantly correlated and not significantly different from each other for the CN and IC. Neural filter bandwidths were variable across units and structures, possibly reflecting heterogeneity of neuronal encoding strategies. These findings support a model in which behavioral frequency selectivity is established early in the auditory pathway. These data form the baseline for ongoing studies of macaques with noise-induced hearing loss and future studies of emerging hearing loss therapeutics.
OF MICE AND MONKEYS: TRANSLATING ANIMAL RESEARCH TO THE CLINIC
American Academy of Audiology
AAA 2018 Conference Nashville, TN
April 20, 2018
As clinical audiology continues to rapidly evolve, animal research is receiving more attention and becoming more clinically pertinent. This session will survey a sample of current hearing research efforts that utilize basic scientific techniques and animal models. Topics will include hair cell regeneration, therapeutic treatments for sensorineural hearing loss, and synaptopathy (i.e. hidden hearing loss). Attendees will learn practical tips on how to critically consume and communicate this knowledge to patients in the clinic.
SENSORY SYSTEM SYNERGY: PUTTING INFORMATION TOGETHER AND WHAT HAPPENS WHEN INPUTS DECLINE
Osher Lifelong Learning Series
March 29, 2018
This lecture, presented in collaboration with Iliza Butera, was first in the neuroscience course offering for the Osher Lifelong Learning Series presented by Vanderbilt University. In the first half, I discussed topics including: the visual system, the auditory system, sensory processing in the brain, mechanisms of peripheral vision and hearing loss, and the neural consequences of sensory deprivation. In the second half, Iliza discussed multisensory integration, multisensory processing by cochlear implant recipients, and scientifically-curated music for cochlear implant users.
GRADUATE RESEARCH ASSISTANT,
August 2017 - present
Mentor: Ramnarayan Ramachandran
Performing invasive single-unit neurophysiology experiments during simultaneous behavioral psychoacoustic tasks to determine the neural correlates of noise-induced hearing loss in macaque monkeys. Presenting results as poster and lecture presentations at institutional and national research conferences. Writing and publishing manuscripts in peer-reviewed journals.
GRADUATE RESEARCH ASSISTANT,
August 2017 - present
Mentor: Geoff Woodman
Investigated visual working memory using a visual change detection task while recording electroencephalography (EEG). Used event related potentials (ERP) to examine contralateral delay activity (CDA) for letters and colored squares. Analyzed data using using custom Matlab scripts and EEGLab.
DEPARTMENT OF OTOLARYNGOLOGY
Medical University of South Carolina,
October 2016 - April 2017
Mentors: Teddy McRackan and Meredith Holcomb
Investigating relationships between pre-operative unaided and aided word recognition scores in cochlear implant recipients. Compiling a center database of cochlear implant recipients for analysis of pre-operative characteristics. Analyzing post-operative outcomes for individuals who underwent cochlear reimplantation. Writing manuscripts of these investigations for publication in peer-reviewed journals.
AUDIOLOGY RESEARCH ASSISTANT,
DEPT. OF HEARING & SPEECH SCIENCES
September 2014 - May 2016
Mentor: Ramnarayan Ramachandran
Performed experiments on macaque monkeys to investigate changes in the peripheral and central auditory system following noise-induced hearing loss. Recorded neurophysiological responses from single units in the inferior colliculus and cochlear nucleus of awake and behaving monkeys during auditory detection tasks. Developed a nonhuman primate model of noise-induced hearing loss to investigate changes in neural circuitry following peripheral auditory damage. Presented results in lecture presentations and poster presentations at Association for Research in Otolaryngology meetings and as a lecture presentation to fellow audiology students, clinicians, and faculty for completion of capstone project. Wrote manuscripts of these investigations for publication in a peer-reviewed journal.
NIH T35 RESEARCH TRAINEE
May - June 2014
Mentor: Ramnarayan Ramachandran
Completed two research projects that investigated hearing in macaque monkeys utilizing audiological and psychophysical approaches. Presented research findings in a cumulative presentation at the end of the traineeship to fellow trainees and department faculty and a poster presentation at the 2015 American Auditory Society Meeting. Prepared manuscript for submission to peer-reviewed research journal.
AUDIOLOGY RESEARCH ASSISTANT,
DEPT. OF HEARING & SPEECH SCIENCES
September 2013 - April 2014
Mentor: René Gifford
Compiled center database for studies of adult cochlear implantation and alternative mapping strategy outcomes. Attended laboratory meetings and contributed to project development and analysis within the lab.
UNDERGRADUATE RESEARCH ASSISTANT,
St. Olaf College,
September 2010 - May 2013
Mentor: Jeremy Loebach
Recorded and processed auditory stimuli of words and sentences to be used for cochlear implant simulation research. Administered experimental studies of lip reading and auditory training to undergraduate students. Strengthened communication skills through explanations of experimental procedures and tasks to students. Gained experience in data analysis using SPSS and Excel spreadsheets. Designed and presented research posters at regional conferences.
Mayo Clinic, Rochester, MN
June - August 2012
Mentor: Doug Sladen
Administered a study that examined how children with normal hearing and children with cochlear implants hear speech in noise. Interacted professionally with children and families to perform cognitive and listening assessments. Shadowed professionals in a variety of fields concerning hearing, including audiology, speech language pathology, vocal rehabilitation, and otolaryngology. Observed a cochlear implant surgery and patient care.
AWARDS, HONORS, AND DISTINCTIONS
NEUROSCIENCE RETREAT BEST TALK AWARD WINNER
Vanderbilt Brain Institute,
NEUROSCIENCE RETREAT POSTER AWARD WINNER
Vanderbilt Brain Institute, September 2017
UNIVERSITY GRADUATE FELLOWSHIP
2017 to present
AUDIOLOGY CAPSTONE AWARD WINNER
POSTER BLITZ FIRST PLACE WINNER
Association for Research in Otolaryngology,
VANDERBILT TUITION SCHOLARSHIP
Vanderbilt University, 2013-2017
DEPARTMENT OF EDUCATION TRAINING GRANT
Vanderbilt University, 2013-2016