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

Abstract

Deafness in both ears is highly disruptive to communication in everyday listening situations. Many individuals with profound deafness receive bilateral cochlear implants (CIs) to gain access to spatial cues used in localization and speech understanding in noise. However, the benefit of bilateral CIs, in particular sensitivity to interaural time and level differences (ITD and ILDs), varies among patients. We measured binaural sensitivity in 46 adult bilateral CI patients to explore the relationship between binaural sensitivity and three classes of patient-related factors: age, acoustic exposure, and electric hearing experience. Results show that ILD sensitivity increased with shorter years of acoustic exposure, younger age at testing, or an interaction between these factors, moderated by the duration of bilateral hearing impairment. ITD sensitivity was impacted by a moderating effect between years of bilateral hearing impairment and CI experience. When age at onset of deafness was treated as two categories (<18 vs. >18 years of age), there was no clear effect for ILD sensitivity, but some differences were observed for ITD sensitivity. Our findings imply that maximal binaural sensitivity is obtained by listeners with a shorter bilateral hearing impairment, a longer duration of CI experience, and potentially a younger age at testing. 198/200.

Keywords: binaural sensitivity; cochlear implant; hearing loss.

Figure 1

A schematic depicting the calculation for each factor investigated.

Figure 2

Box plots depicting (A) Interaural level difference (ILD) Just-noticeable differences (JNDs) for each electrode pair that was tested. Data shown have all ILD JNDs, including JNDs that could not be determined. Medians represent the data with only JNDs below 20 CUs. Black dashed line indicates the “could not determine” (CND) mark for JNDs > 20 CU. (B) Box plots depicting ITD JNDs for each electrode pair that was tested. Data shown have all ITD JNDs, including JNDs that could not be determined. Medians represent the data with only measurable thresholds. Black dashed line indicates the CND mark for JNDs. Subject IBX who was tested with 2000 μs had a JND that exceeded 1600 μs, and therefore the open-circle symbol represents subject IBX.

Figure 3

Shows (A) ILD Just-noticeable differences (JNDs) as a function of years of acoustic exposure and years of bilateral hearing impairment. Blue-colored symbols indicate fewer years of bilateral hearing impairment and orange-colored symbols indicate greater years of bilateral hearing impairment. (B) Shows ILD JNDs as a function of age at testing and years of bilateral hearing impairment. Blue-colored symbols indicate fewer years of bilateral hearing impairment and orange-colored symbols indicate greater years of bilateral hearing impairment.

Figure 4

Shows ITD Just noticeable differences (JNDs) as a function of years of bilateral hearing impairment and years with at least one CI. Blue-colored symbols indicate fewer years with at least one CI and yellow-colored symbols indicate greater years of with at least one CI.

Figure 5

Shows the distribution of (A) ILD Just-noticeable differences (JNDs) as a box plot and violin plot for all listeners as a function of age at onset of deafness group. A wider distribution (i.e., greater thickness) on a violin plot corresponds to a greater number of listeners with a given JND on the y-axis. Black dashed line indicates “could not determine” (CND) threshold for ILD JNDs; (B) shows histograms of ILD JNDs, for each age group, binned according to levels of performance ranging from “good” (< 2 CUs) to “poor” (>10 CUs).

Figure 6

Shows the distribution of (A) ITD Just-noticeable differences (JNDs) as a box plot and violin plot for all listeners as a function of age at onset of the deafness group. A wider distribution (i.e., greater thickness) on a violin plot corresponds to a greater number of listeners with a given JND on the y-axis. Black dashed line indicates “could not determine” (CND) threshold for ITD JNDs. (B) Shows histograms of ITD JNDs, for each age group, binned according to levels of performance ranging from “good” (<200 μs) to “poor” (>1600 μs).

Figure 7

Comparison of ITD and ILD Just-noticeable differences (JNDs) as a function of years of bilateral hearing impairment. Blue-colored symbols indicate fewer years of bilateral hearing impairment and orange-colored symbols indicate greater years of bilateral hearing impairment.