Interaction Between Electric and Acoustic Stimulation Influences Speech Perception in Ipsilateral EAS Users

Abstract

Objectives: The aim of this study was to determine electric-acoustic masking in cochlear implant users with ipsilateral residual hearing and different electrode insertion depths and to investigate the influence on speech reception. The effects of different fitting strategies—meet, overlap, and a newly developed masking adjusted fitting (UNMASKfit)—on speech reception are compared. If electric-acoustic masking has a detrimental effect on speech reception, the individualized UNMASKfit map might be able to reduce masking and thereby enhance speech reception. Design: Fifteen experienced MED-EL Flex electrode recipients with ipsilateral residual hearing participated in a crosssover design study using three fitting strategies for 4 weeks each. The following strategies were compared: (1) a meet fitting, dividing the frequency range between electric and acoustic stimulation, (2) an overlap fitting, delivering part of the frequency range both acoustically and electrically, and (3) the UNMASKfit, reducing the electric stimulation according to the individual electric-on-acoustic masking strength. A psychoacoustic masking procedure was used to measure the changes in acoustic thresholds due to the presence of electric maskers. Speech reception was measured in noise with the Oldenburg Matrix Sentence test. Results: Behavioral thresholds of acoustic probe tones were significantly elevated in the presence of electric maskers. A maximum of masking was observed when the difference in location between the electric and acoustic stimulation was around one octave in place frequency. Speech reception scores and strength of masking showed a dependency on residual hearing, and speech reception was significantly reduced in the overlap fitting strategy. Electric- acoustic stimulation significantly improved speech reception over electric stimulation alone, with a tendency toward a larger benefit with the UNMASKfit map. In addition, masking was significantly inversely correlated to the speech reception performance difference between the overlap and the meet fitting. Conclusions: (1) This study confirmed the interaction between ipsilateral electric and acoustic stimulation in a psychoacoustic masking experiment. (2) The overlap fitting yielded poorer speech reception performance in stationary noise especially in subjects with strong masking. (3) The newly developed UNMASKfit strategy yielded similar speech reception thresholds with an enhanced acoustic benefit, while at the same time reducing the electric stimulation. This could be beneficial in the long-term if applied as a standard fitting, as hair cells are exposed to less possibly adverse electric stimulation. In this study, the UNMASKfit allowed the participants a better use of their natural hearing even after 1 month of adaptation. It might be feasible to transfer these results to the clinic, by fitting patients with the UNMASKfit upon their first fitting appointment, so that longer adapta...

Robust data-driven auditory profiling towards precision audiology

“…The criteria for candidacy of implantable technology (Kirkby-Strachan and Que-Hee 2016; Irving et al 2014), which are based on the benefit observed by using acoustical devices, are sometimes insufficient. New findings with electro-acoustic stimulation (Imsiecke et al 2019) suggest that this technology might benefit patients with a high degree of speech-intelligibility related deficits, i.e. with HL HF > 50 dB HL as shown here.…”

“…with HL HF > 50 dB HL as shown here. Despite the detrimental effect of the interaction between electrical and acoustical stimulations, Imsiecke et al (2019) showed that the use of masking-adjusted fittings with the aim of reducing electric-on acoustic masking strength was beneficial for speech intelligibility even in the cases with good residual hearing. Therefore, the present characterization into auditory profiles might support a revision of the candidacy of implantable devices that might include less severe hearing losses at high frequencies.…”

Phantom Stimulation for Cochlear Implant Users With Residual Low-Frequency Hearing

“…In contrast, the current study extended the bandwidth through an additional phantom channel which allowed the use of the same electrode-frequency allocation for all other CI channels. Therefore, the subjects of the current study may have been less influenced by acclimatization effects when using the extended and the restricted bandwidth in comparison to the subjects tested in the previous studies of Imsiecke et al (2020), Karsten et al (2013), and Reiss et al (2012). For this reason, we observed significant differences when extending the bandwidth using EPS.…”

“…Krüger et al (2017) showed that EAS masking increases with decreasing distance between the stimulation site of electric and acoustic stimulation in the cochlea, the so-called electric-acoustic frequency difference (EAFD). Imsiecke et al (2020) showed a correlation between psychoacoustic EAS masking and the deterioration in speech perception for EAS subjects fitted with a spectral overlap. Moreover, Saoji et al (2018) observed that phantom stimulation increases masking between electric and acoustic stimulation.…”

“…The EAS users tested by Kiefer et al (2005) performed better using the overlap condition whereas Vermeire et al (2008) observed better speech perception for EAS users with separated frequency bandwidths. Karsten et al (2013) and Imsiecke et al (2020) compared speech perception of EAS users when the spectral bandwidth associated with electric and acoustic stimulation were partially overlapped by lowering the CI’s cutoff frequency used for electric stimulation to a specific amount of 50% or 2 octaves, respectively. Both studies observed a significant decrement in performance for the overlap bandwidth condition when listening through EAS.…”