Spectral and temporal measures in hybrid cochlear implant users: on the mechanism of electroacoustic hearing benefits

Abstract

Objective: Compare auditory performance of Hybrid and standard cochlear implant users with psychoacoustic measures of spectral and temporal sensitivity and correlate with measures of clinical benefit.

Study design: Cross-sectional study.

Setting: Tertiary academic medical center.

Patients: Hybrid cochlear implant users between 12 and 33 months after implantation. Hybrid recipients had preservation of low-frequency hearing.

Interventions: Administration of psychoacoustic, music perception, and speech reception in noise tests.

Main outcome measures: Performance on spectral-ripple discrimination, temporal modulation detection, Schroeder-phase discrimination, Clinical Assessment of Music Perception, and speech reception in steady-state noise tests.

Results: Clinical Assessment of Music Perception pitch performance at 262 Hz was significantly better in Hybrid users compared with standard implant controls. There was a near significant difference on speech reception in steady-state noise. Surprisingly, neither Schroeder-phase discrimination at 2 frequencies nor temporal modulation detection thresholds across a range of frequencies revealed any advantage in Hybrid users. This contrasts with spectral-ripple measures that were significantly better in the Hybrid group. The spectral-ripple advantage was preserved even when using only residual hearing.

Conclusion: These preliminary data confirm existing data demonstrating that residual low-frequency acoustic hearing is advantageous for pitch perception. Results also suggest that clinical benefits enjoyed by Hybrid recipients are due to improved spectral discrimination provided by the residual hearing. No evidence indicated that residual hearing provided temporal information beyond that provided by electric stimulation.

FIG. 1

A, Individual pure tone audiograms for the subjects’ implanted ear. B, Individual pure tone audiograms for the subjects’ nonimplanted ear.

FIG. 2

Spectral-ripple discrimination test performance. Higher scores indicate better performance. *Significant difference between Hybrid users and standard cochlear implant users. (EA, electroacoustic; A, acoustic; error bars are SEM)

FIG. 3

Speech reception threshold (SRT) performance. Lower (more negative) scores indicate better performance. (EA, electroacoustic; SNR, signal-to-noise ratio; error bars are SEM)

FIG. 4

University of Washington Clinical Assessment of Music Perception (UW-CAMP) performance. A, Melody test. B, Pitch test. Lower scores indicate better performance. C, Timbre test. *Significant difference between Hybrid users and standard cochlear implant users. (p<0.05) (EA, electroacoustic; error bars are SEM)

FIG. 5

Schroeder-phase discrimination performance. A, 50 Hz. B, 200 Hz. Chance level is 50%. Higher scores indicate better performance. Previously published hearing impaired and normal data are displayed for reference. (EA, electroacoustic, HI, hearing impaired; error bars are SEM)

FIG. 6

Temporal modulation detection test performance. *Significant difference between Hybrid users and standard cochlear implant users. Lower (more negative) scores indicate better performance. Previously published hearing impaired and normal data are displayed for reference. (EA, electroacoustic, HI, hearing impaired; error bars are SEM)