Binaural diplacusis in individuals with suspected endolymphatic hydrops

Define interaural pitch matching in individuals with suspected endolymphatic hydrops (sus-EH) and evaluate the stability of interaural pitch comparisons over time.

Sixteen adults with clinically diagnosed Ménière's disease or otherwise suspected EH (10 unilateral, 6 bilateral; aged 32-65 years) and 14 normal-hearing controls (aged 20-53 years) completed an adaptive binaural pitch-comparison task at three low-to-mid frequencies (≤1500 Hz). Using a two-alternative forced-choice paradigm, participants indicated whether sequential tones presented to each ear were higher or lower in pitch. For the unilateral sus-EH group, reference tones were presented to the unaffected ear and variable test tones to the ear with suspected EH. Psychometric functions determined the matching frequency where perceived pitch equality occurred between right and left ears. Interaural frequency shifts were calculated as the difference between matching and reference-tone frequencies. Test-retest repeatability of interaural frequency shifts was assessed over a mean interval of 5 months.

Normal-hearing controls demonstrated minimal interaural frequency shifts (mean = 12 cents, SD = 35 cents). The unilateral sus-EH group showed significantly larger positive frequency shifts (mean = 116 cents, SD = 170 cents), indicating that higher-frequency tones in the suspected EH ear were needed to match the pitch of reference tones in the healthy ear. This pattern is consistent with an apical shift in the cochlear frequency-place map. Subjects in the bilateral sus-EH group exhibited near-zero mean shifts (mean = -34 cents, SD = 117 cents), suggesting similar pathology in both ears. A two-way ANOVA confirmed a main effect of group indicating that frequency shifts were significantly larger in the unilateral sus-EH group compared to controls. Repeatability of frequency shifts in sus-EH groups was poorer than that of controls (p < 0.001), with the bilateral sus-EH group showing the highest test-retest variation (mean = 169 cents, SD = 151 cents).

Interaural pitch comparisons were an efficient method for detecting perceptual abnormalities in a group with suspected endolymphatic hydrops. Results suggest an overall group trend for the presence of binaural diplacusis in this group, although there was significant variability across individuals. The interaural frequency shifts observed are consistent with the hypothesis that endolymphatic hydrops associated with Ménière's disease can cause mechanical alterations in the cochlear partition, producing an apical-ward shift of the cochlear frequency-place map. The increased across-subject variability and poorer repeatability of measurements in the sus-EH group are consistent with the fluctuating and episodic nature of the disease.