JARO Research News

spARO volunteers are submitting Research News highlights about recent articles published in JARO, our society's journal. If you are interested in joining this effort, please contact the Publication's Committee representative from spARO (Mary O’Sullivan, mary29(at)stanford.edu). Members can find guidelines for submitting a JARO Research News report here.


August 2019

A New Model for Congenital Vestibular Disorders

Sigmund J. Lilian, Hayley E. Seal, Anastas Popratiloff, June C. Hirsch, and Kenna D. Peusner

Lilian, S.J., Seal, H.E., Popratiloff, A., Hirsch, J.C. & Peusner, K.D. JARO (2019) 20: 133. https://doi.org/10.1007/s10162-018-00705-z

Reported by:  Lukas D. Landegger, M.D., Ph.D. Medical University of Vienna, Department of Otorhinolaryngology-Head and Neck Surgery

 

Figure A:  Paint fills of inner ears on embryonic day 13 show differences between normal (a) and sac-like ARO chicks (b,c).  From Lilian et al., 2019, JARO 20: 133-149.

 

 Congenital vestibular disorders comprise a range of inner ear pathologies, hampered motor development, and balance and posture problems. Apart from mouse models of congenital vestibular disorders, until recently, no appropriate animal model had been established, which limited the study of central vestibular circuits. The rewiring of these neural connections has important ramifications for the understanding and potential subsequent therapy of these debilitating conditions.

In their recent publication, Lilian et al. describe a chick embryo model allowing them to analyze the developing vestibular system in the above-mentioned disorders. By surgically rotating the otocyst (a structure that gives rise to the inner ear) of 2-day-old chick embryos (180° in the anterior-posterior axis), they form the “anterior-posterior axis rotated otocyst” or ARO chick (a tip of the hat to our scientific society, perhaps?). In this model, a reproducible pathology of a sac with truncated/missing semicircular canals can be induced (Figure A), which represents the most prevalent inner ear defect in pediatric patients with congenital vestibular disorders.

Meticulous analysis of the resulting anatomy in embryonic day 13 ARO chicks led the researchers to discover that the sac contains all five vestibular organs (maculae utriculi and sacculi as well as three cristae), but the macula utriculi and superior crista are shortened along the anterior-posterior axis. Additional changes are not just restricted to the inner ear but also include a synaptic station in the brainstem that receives vestibular input from inner ear: the tangential nucleus demonstrates a 66% reduction in the number of principal cells on the rotated side.

These anatomical changes are accompanied by a subset of behavioral deficits: the ARO chicks have a constant right head tilt and gait problems (stumbling and walking with a widened base; Figure B), mimicking some human forms of congenital vestibular disorders. In contrast, the righting reflex times after hatching are unaffected, with no difference observed between control and ARO chicks.

This novel technique appears to be relatively straightforward and gives researchers an important tool to assess the resulting changes in the central nervous system, which should hopefully help to develop new treatments for people affected by congenital vestibular disorders.

 

Figure B.  5-day hatchling chicks show differences between a normal animal (a) and an ARO chick with a head tilt at rest (b) and a widened stance after performing a righting reflex (c). From Lilian et al., 2019, JARO 20: 133-149.

 

 


June 2019

Interaction Between Pitch and Timbre Perception in Normal-Hearing Listeners and Cochlear Implant Users

Xin Luo, Samara Soslowsky, and Kathryn R.Pulling

Luo, X., Soslowsky, S. & Pulling, K.R. JARO (2019) 20: 57.  https://doi.org/10.1007/s10162-018-00701-3

Reported by:
Karen Chan Barrett, Ph.D. & Nicole Jiam, M.D.
University of California, San Francisco, Department of Otolaryngology-Head and Neck Surgery

Cochlear implant (CI) users find it difficult to enjoy music, and a new paper by Luo et al. explores their struggles with perception of certain acoustic dimensions. Using an innovative approach, the authors studied the interaction between pitch and timbre perception, rather than treating these two features independently.  Pitch is the perceptual correlate of fundamental frequency (or F0); timbre refers to the quality of a sound as distinct from pitch or intensity that helps to differentiate instruments or speakers from one another. In normal hearing (NH) adults, musical chords are perceived differently when played on different instruments1 and non-musician adults have a difficult time rapidly categorizing stimuli based on pitch or timbre, often confusing the two.2  In the current study, the authors designed two experiments to evaluate the relationship between pitch and timbre perception in non-musical NH listeners and CI users.  Both designs revealed better performance when the two acoustic dimensions were varied congruently (as expected for human musical predilections) rather than incongruently, despite an overall worse performance by CI users.

In experiment 1, participants completed tasks to determine fundamental frequency (F0) and spectral slope (timbre correlate) difference limens (DLs) without variations in the non-target dimension. Pitch and sharpness rankings were then separately tested when the F0 and the spectral slope of harmonic complex tones varied by the same multiple of individual DLs either congruently (e.g. higher pitch accompanied with a sharper timbre or a lower pitch with a duller timbre) or incongruently (e.g. higher pitch with a duller timbre). In general, CI users had poorer timbre and pitch perception compared to NH adults. Additionally, a symmetric and bidirectional interaction between pitch and timbre perception was found in that better performance was seen for congruent F0 and spectral slope variations. In experiment 2, CI users performed melodic contour identification (MCI) of harmonic complex tones with or without spectral slope variations.  All participants repeated pitch and timbre discrimination tasks to obtain F0 and spectral slope limens, and then completed the MCI task where the contours either had no spectral slope variations, congruent variations (i.e. spectral slope and F0 increased together or decreased together), or incongruent variations (i.e. spectral slope and F0 moved in opposite directions).  Results again demonstrated an interaction between pitch and timbre; better performance was found for congruent stimuli.  Additionally, MCI performance was significantly degraded with amplitude roving, suggesting that there may also be a perceptual interaction between loudness and pitch cues. 

In summary, this study is notable in that it explores how acoustic dimensions interact and are perceived by CI users, a crucial step towards a deeper understanding of complex sound perception in implantees. These findings are significant because they may have implications for future methods to improve music enjoyment in CI users.

1.     Beal AL. The skill of recognizing musical structures. Mem Cognit. 1985 Sep;13(5):405–12.
2.     Pitt MA. Perception of pitch and timbre by musically trained and untrained listeners. J Exp Psychol Hum Percept Perform. 1994 Oct; 20(5):976–86.