PP322 - When Two Tones Do Not Sound the Same in the Two Ears: How Can We Measure Diplacusis in Musicians

Abstract:
Diplacusis is a perceptual anomaly in which the same sound is perceived as having a different pitch depending on whether it is presented in the right or left ear. The aim of our study is to develop and test a protocol for the clinical assessment of diplacusis, and to collect normative data in normal-hearing adults with and without musical training. This protocol will help audiologists to better assess musicians' hearing difficulties and allow a better management.

Summary:
Rationale
Diplacusis refers to a perceptual anomaly whereby the same tone is perceived as having a different pitch depending on whether it is presented in the right or in the left ear in the same listener. Prevalence studies are scarce but diplacusis is estimated to lay between 2 and 8% in professional musicians. This disorder is potentially detrimental to musicianship and is not assessed in the clinic. Our aim is to develop a test with good psychoacoustic properties but feasible in the context of a clinical assessment.

Design
The task has three steps. The first step is to establish each ear’s threshold using tonal audiometry. The better ear will serve as the reference ear (RE), and the worse ear as the tested ear (TE).  The second step is to match loudness between ears for each tested frequency since loudness can influence pitch perception and increase  false positives of diplacusis. The third step requires the listener to actively listen and match pitches between ears for the standard range of ten frequencies from 250Hz to 8kHz. Three visual sliders are used to increase levels of pitch granularity and improve accuracy.

Results
Our protocol has been developed and converted in a setup compatible with equipment easily available in the clinic, namely, a computer with a standard soundcard, a screen, a mouse, and supra-aural headphones. Non-musicians and musicians with normal hearing are being tested on a beta version. Preliminary data indicate greater variability among nonmusicians than among musicians (e.g., 15 Hz vs. 2 Hz at 250 Hz and 606 Hz vs. 430 Hz at 8 kHz, respectively).  As frequencies increased pitch matching accuracy generally decreased, aligning with the increasing critical bandwidths at higher center frequencies.

Conclusions
Musicians have better pitch matching abilities than nonmusicians. It is important to have separate normative data for these two groups in order to capture potential diplacusis. Our tool seems appropriate to accurately measure pitch matching in a playful and active mode. Audiologists who often assess musicians’ hearing could benefit to have tools to personalize and specialize their management.