Psychophysically based site selection coupled with dichotic stimulation improves speech recognition in noise with bilateral cochlear implants

Abstract

The ability to perceive important features of electrical stimulation varies across stimulation sites within a multichannel implant. The aim of this study was to optimize speech processor MAPs for bilateral implant users by identifying and removing sites with poor psychophysical performance. The psychophysical assessment involved amplitude-modulation detection with and without a masker, and a channel interaction measure quantified as the elevation in modulation detection thresholds in the presence of the masker. Three experimental MAPs were created on an individual-subject basis using data from one of the three psychophysical measures. These experimental MAPs improved the mean psychophysical acuity across the electrode array and provided additional advantages such as increasing spatial separations between electrodes and/or preserving frequency resolution. All 8 subjects showed improved speech recognition in noise with one or more experimental MAPs over their everyday-use clinical MAP. For most subjects, phoneme and sentence recognition in noise were significantly improved by a dichotic experimental MAP that provided better mean psychophysical acuity, a balanced distribution of selected stimulation sites, and preserved frequency resolution. The site-selection strategies serve as useful tools for evaluating the importance of psychophysical acuities needed for good speech recognition in implant users.

Comparison of the Spectral-Temporally Modulated Ripple Test With the Arizona Biomedical Institute Sentence Test in Cochlear Implant Users

“…Although both spectral resolution and temporal amplitude modulation sensitivity could potentially account for the correlation with speech recognition (Friesen et al 2001; Won et al 2007; Fu 2002; Luo et al 2008; Zhou & Pfingst 2012) it is not possible to distinguish the contributions of each based on the current experiment. Future studies will need to independently manipulate these factors to determine how they each contribute.…”

“…Single-channel amplitude modulation detection has been found to correlate with speech perception (Fu 2002; Luo et al 2008). Additionally, removing channels with poor amplitude modulation sensitivity can improve speech perception (Zhou & Pfingst 2012). …”

The Effect of Interleaved Filters on Normal Hearing Listeners’ Perception of Binaural Cues

“…Sending signals from neighboring frequency regions to opposite ears (interleaving) helps listeners with sensorineural hearing loss, HA users, and some CI users perform better in noisy environments (Kulkarni et al 2012; Lunner et al 1993; Tyler et al 2010; Zhou et al 2012). However, interleaving potentially adversely affects both interaural time difference (ITD) and interaural level difference (ILD) cues because both rely, to varying degrees, on overlapping areas of excitation across ears (Francart et al 2007; Poon et al 2009).…”

Interleaved Processors Improve Cochlear Implant Patients’ Spectral Resolution

“…The importance of pitch matching the arrays is consistent with results from simulations of interleaved processors with NH listeners, where the benefits of interleaved processors depended on starting with perceptually aligned channels (Siciliano et al 2010). Although interleaved processors aligned based on electrode number have been shown to yield improvements when combined with the removal of sub-optimal channels based on modulation detection (Zhou and Pfingst 2012), that improvement may reflect the removal of the sub-optimal channels rather than the use of interleaving.…”

“…One method that has been used with a number of populations to reduce within-ear masking either from channel interaction or from the spread of masking is to interleave the spectral information across ears (Aronoff et al 2014; Kulkarni et al 2012; Loizou et al 2003; Lunner et al 1993; Siciliano et al 2010; Takagi et al 2010; Tyler et al 2010; Zhou and Pfingst 2012; Zhou and Xu 2011). This means that the spectrum is divided into two interleaved groups.…”