The Relationship Between Intensity Coding and Binaural Sensitivity in Adults With Cochlear Implants

Abstract

Objectives Many bilateral cochlear implant users show sensitivity to binaural information when stimulation is provided using a pair of synchronized electrodes. However, there is large variability in binaural sensitivity between and within participants across stimulation sites in the cochlea. It was hypothesized that within-participant variability in binaural sensitivity is in part affected by limitations and characteristics of the auditory periphery which may be reflected by monaural hearing performance. The objective of this study was to examine the relationship between monaural and binaural hearing performance within participants with bilateral cochlear implants. Design Binaural measures included dichotic signal detection and interaural time difference discrimination thresholds. Diotic signal detection thresholds were also measured. Monaural measures included dynamic range and amplitude modulation detection. In addition, loudness growth was compared between ears. Measures were made at three stimulation sites per listener. Results Greater binaural sensitivity was found with larger dynamic ranges. Poorer interaural time difference discrimination was found with larger difference between comfortable levels of the two ears. In addition, poorer diotic signal detection thresholds were found with larger differences between the dynamic ranges of the two ears. No relationship was found between amplitude modulation detection thresholds or symmetry of loudness growth and the binaural measures. Conclusions The results suggest that some of the variability in binaural hearing performance within listeners across stimulation sites can be explained by factors non-specific to binaural processing. The results are consistent with the idea that dynamic range and comfortable levels relate to peripheral neural survival and the width of the excitation pattern which could affect the fidelity with which central binaural nuclei process bilateral inputs.

Polarity Sensitivity in Pediatric and Adult Cochlear Implant Listeners

“…Notably, CI listeners programmed with larger electrical DRs have better speech perception scores (Bento et al., 2005; Fu & Shannon, 2000; Loizou, Dorman, & Fitzke, 2000; Zeng & Galvin, 1999) and better binaural sensitivity (Todd, Goupell, & Litovsky, 2017) than those with smaller electrical DRs. We performed an exploratory regression analysis to determine whether the DRs for cathodic or anodic stimuli were correlated with vowel identification performance in this sample of CI listeners.…”

Interaural asymmetry of dynamic range: Abnormal fusion, bilateral interference, and shifts in attention

“…The ear with poorer temporal fidelity predicted the amount of sensitivity to binaural cues ( Ihlefeld et al, 2015 ; Anderson et al, 2019b , 2022 ). Simulations in NH used asymmetric dynamic range (i.e., amplitude modulation depth), where smaller dynamic ranges in listeners with BiCIs have resulted in poorer sensitivity to binaural cues ( Ihlefeld et al, 2014 ; Todd et al, 2017 ). In these studies, performance with the poorer ear was predictive of the binaural benefit, suggesting that if one ear is poorly performing, it can act as a bottleneck that limits encoding of information which is used in binaural processing.…”

“…The dynamic range of each electrode varies across listeners ( Long et al, 2014 ). Smaller dynamic ranges result in poorer speech understanding ( Firszt et al, 2002 ; Spahr et al, 2007 ) and binaural processing ( Ihlefeld et al, 2014 ; Todd et al, 2017 ) for listeners with BiCIs. We simulated CI processing using a vocoder and manipulated the dynamic range of the speech in each ear symmetrically or asymmetrically.…”

Evaluating the Impact of Age, Acoustic Exposure, and Electrical Stimulation on Binaural Sensitivity in Adult Bilateral Cochlear Implant Patients

“…Thus, the ability to achieve good spatial hearing skills depends on normal and early access to acoustic cues. In contrast, children who are deaf and hear through CIs do not have an opportunity to experience normal inputs from a young age and have poorer spatial hearing skills and reduced sensitivity to binaural cues [ 37 , 62 , 63 , 64 ]. Further, in children with bilateral CIs, ITD sensitivity is generally poor or non-existent when binaural inputs are disrupted in infancy, while ILD sensitivity is generally found in all children regardless of their early auditory experience.…”