Acoustic Cue Weighting by Adults with Cochlear Implants: A Mismatch Negativity Study

Abstract

Objectives Formant Rise Time (FRT) and Amplitude Rise Time (ART) are acoustic cues that inform phonetic identity. FRT represents the rate of transition of the formant(s) to a steady state, while ART represents the rate at which the sound reaches its peak amplitude. Normal hearing (NH) native English speakers weight FRT more than ART during the perceptual labeling of the /bα/-/wα/ contrast. This weighting strategy is reflected neurophysiologically in the magnitude of the mismatch negativity (MMN) – MMN is larger during the FRT than the ART distinction. The present study examined the neurophysiological basis of acoustic cue weighting in adult cochlear implant (CI) listeners using the MMN design. It was hypothesized that individuals with CIs who weight ART more in behavioral labeling (ART-users) would show larger MMNs during the ART than the FRT contrast, and the opposite would be seen for FRT-users. Design Electroencephalography (EEG) was recorded while twenty adults with CIs listened passively to combinations of three synthetic speech stimuli: a /bα/ with /bα/-like FRT and ART; a /wα/ with /wα/-like FRT and ART; and a /bα/wa stimulus with /bα/-like FRT and /wα/-like ART. The MMN response was elicited during the FRT contrast by having participants passively listen to a train of /wα/ stimuli interrupted occasionally by /bα/wa stimuli, and vice versa. For the ART contrast, the same procedure was implemented using the /bα/ and /bα/wa stimuli. Results Both ART- and FRT-users with CIs elicited MMNs that were equal in magnitudes during FRT and ART contrasts, with the exception that FRT-users exhibited MMNs for ART and FRT contrasts that were temporally segregated. That is, their MMNs occurred significantly earlier during the ART contrast (~100 ms following sound onset) than during the FRT contrast (~200ms). In contrast, the MMNs for ART-users of both contrasts occurred later and were not significantly separable in time (~230 ms). Interestingly, this temporal segregation observed in FRT-users is consistent with the MMN behavior in NH listeners. Conclusions Results suggest that listeners with CIs who learn to classify phonemes based on formant dynamics, consistent with NH listeners, develop a strategy similar to NH listeners, in which the organization of the amplitude and spectral representations of phonemes in auditory memory are temporally segregated.

Learning Effects in Psychophysical Tests of Spectral and Temporal Resolution

“…Because the study population in this study participated in a clinical trial between baseline and retest measurements, they did get a chance to adapt to different speech cues and learn new auditory percepts. This perceptual learning could have potentially been used in the spectral and/or temporal discrimination tasks (Moberly et al 2015). On the other hand, speech scores were also assessed during this trial, for which no improvement was observed (F1,9=0.826, p=0.387).…”

“…It is plausible that this improvement is caused by 'perceptual learning', which is a process by which the ability of the auditory system to process stimuli is improved through experience. Also Moberly et al (2015) suggested that CI users could learn from new speech cues, which might be present in novel speech coding strategies. Repeated testing with the SMRT and MDT test in a research setting with multiple novel speech coding strategies could, therefore, lead to both task and perceptual learning and consequently to improved SMRT and MDT performance.…”

Neural Mechanisms of Hearing Recovery for Cochlear-Implanted Patients: An Electroencephalogram Follow-Up Study

“…In addition, the MMN reflects a preattentive auditory-evoked potential (AEP) that occurs 100–300 ms following sound onset and is characterized by a front-central negativity elicited during any acoustically discriminable “deviant” sound within a regular stream of “standard” stimuli (C.W. Ponton et al, 2000 ; Näätänen et al, 2007 ; Moberly et al, 2016 ). N1, P2, and MMN are believed to be potential candidates in developing models of auditory information processing.…”

“…The third aim is to investigate MMN in CI users with the increase of implantation time. MMN is thought to represent the brain’s response to a mismatch of the current stimulus representation and a trace in short- or long-term auditory memory ( Naatanen et al, 2011 ; Moberly et al, 2016 ). Nina Kraus et al (1993) studied MMN in nine postlingual adult CI users with/da/and/ta/.…”

Flaws in Spectral Ripple Stimuli for Listeners with Cochlear Implants

“…Phonetic perception can be measured electrophysiologically as well (Moberly et al 2016), for individuals who cannot give behavioral responses (such as infants).…”