Using behavioral data to model open-set word recognition and lexical organization by pediatric cochlear implant users.

Though much is known about how words are recognized, little research has focused on how a degraded signal affects the fine-grained temporal aspects of real-time word recognition. The perception of degraded speech was examined in two populations with the goal of describing the time course of word recognition and lexical competition. Thirty-three postlingually deafened cochlear implant (CI) users and 57 normal hearing (NH) adults (16 in a CI-simulation condition) participated in a visual world paradigm eye-tracking task in which their fixations to a set of phonologically related items were monitored as they heard one item being named. Each degraded-speech group was compared with a set of age-matched NH participants listening to unfiltered speech. CI users and the simulation group showed a delay in activation relative to the NH listeners, and there is weak evidence that the CI users showed differences in the degree of peak and late competitor activation. In general, though, the degraded-speech groups behaved statistically similarly with respect to activation levels.

Spoken words carry linguistic and indexical information to listeners. ionist models of spoken word recognition suggest that indexical information is stripped away in a process called normalization to allow processing of the linguistic message to proceed. In contrast, exemplar models of the lexicon suggest that indexical information is retained in memory, and influences the process of spoken word recognition. In the present study native Spanish listeners heard Spanish words that varied in grammatical gender (masculine, ending in -o, or feminine, ending in -a) produced by either a male or a female speaker. When asked to indicate the grammatical gender of the words, listeners were faster and more accurate when the sex of the speaker “matched” the grammatical gender than when the sex of the speaker and the grammatical gender “mismatched.” No such interference was observed when listeners heard the same stimuli, but identified whether the speaker was male or female. This finding suggests that indexical information, in this case the sex of the speaker, influences not just processes associated with word recognition, but also higher-level processes associated with grammatical processing. This result also raises questions regarding the widespread assumption about the cognitive independence and automatic nature of grammatical processes.

Speech perception relies on auditory and visual cues and there are strong links between speech perception and production. We aimed to evaluate the role of auditory and visual modalities on speech perception and production in adults with impaired hearing or sight versus those with normal hearing and sight. We examined speech perception and production of three isolated vowels (/i/, /y/, /u/), which were selected based on their different auditory and visual perceptual saliencies, in 12 deaf adults who used one or two cochlear implants (CIs), 14 congenitally blind adults, and 16 adults with normal sight and hearing. The results showed that the deaf adults who used a CI had worse vowel identification and discrimination perception and they also produced vowels that were less typical or precise than other participants. They had different tongue positions in speech production, which possibly partly explains the poorer quality of their spoken vowels. Blind individuals had larger lip openings and smaller lip protrusions for the rounded vowel and unrounded vowels, compared to the other participants, but they still produced vowels that were similar to those produced by the adults with normal sight and hearing. In summary, the deaf adults, even though they used CIs, had greater difficulty in producing accurate vowel targets than the blind adults, whereas the blind adults were still able to produce accurate vowel targets, even though they used different articulatory strategies.

Cochlear implantation does not automatically result in robust spoken language understanding for postlingually deafened adults. Enormous outcome variability exists, related to the complexity of understanding spoken language through cochlear implants (CIs), which deliver degraded speech representations. This investigation examined variability in word recognition as explained by "perceptual attention" and "auditory sensitivity" to acoustic cues underlying speech perception. Thirty postlingually deafened adults with CIs and 20 age-matched controls with normal hearing (NH) were tested. Participants underwent assessment of word recognition in quiet and perceptual attention (cue-weighting strategies) based on labeling tasks for two phonemic contrasts: (1) "cop"-"cob," based on a duration cue (easily accessible through CIs) or a dynamic spectral cue (less accessible through CIs), and (2) "sa"-"sha," based on static or dynamic spectral cues (both potentially poorly accessible through CIs). Participants were also assessed for auditory sensitivity to the speech cues underlying those labeling decisions. Word recognition varied widely among CI users (20 to 96%), but it was generally poorer than for NH participants. Implant users and NH controls showed similar perceptual attention and auditory sensitivity to the duration cue, while CI users showed poorer attention and sensitivity to all spectral cues. Both attention and sensitivity to spectral cues predicted variability in word recognition. For CI users, both perceptual attention and auditory sensitivity are important in word recognition. Efforts should be made to better represent spectral cues through implants, while also facilitating attention to these cues through auditory training.

The main goal of this study was to investigate the minimum amount of sensory information required to recognize spoken words (isolation points [IPs]) in listeners with cochlear implants (CIs) and investigate facilitative effects of semantic contexts on the IPs. Listeners with CIs as well as those with normal hearing (NH) participated in the study. In Experiment 1, the CI users listened to unprocessed (full-spectrum) stimuli and individuals with NH listened to full-spectrum or vocoder processed speech. IPs were determined for both groups who listened to gated consonant-nucleus-consonant words that were selected based on lexical properties. In Experiment 2, the role of semantic context on IPs was evaluated. Target stimuli were chosen from the Revised Speech Perception in Noise corpus based on the lexical properties of the final words. The results indicated that spectrotemporal degradations impacted IPs for gated words adversely, and CI users as well as participants with NH listening to vocoded speech had longer IPs than participants with NH who listened to full-spectrum speech. In addition, there was a clear disadvantage due to lack of semantic context in all groups regardless of the spectral composition of the target speech (full spectrum or vocoded). Finally, we showed that CI users (and users with NH with vocoded speech) can overcome such word processing difficulties with the help of semantic context and perform as well as listeners with NH. Word recognition occurs even before the entire word is heard because listeners with NH associate an acoustic input with its mental representation to understand speech. The results of this study provide insight into the role of spectral degradation on the processing of spoken words in isolation and the potential benefits of semantic context. These results may also explain why CI users rely substantially on semantic context.

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ABSTRACTNormal auditory feedback contributes to moment-to-moment control of speech production. Effects of auditory feedback’s absence on hearing-impaired individuals are widely documented, but auditory perturbation has not been investigated. Our objective was to evaluate the effect of delayed auditory feedback (DAF) and frequency altered feedback (FAF) on speech production among prelingual cochlear implant (CI) users and normal hearing (NH) individuals, to evaluate CI users’ reliance on auditory feedback. Twenty young adults (10 CI, 10 NH), without developmental and cognitive impairments, participated in the study. Under variable auditory feedback conditions, speech production (spontaneous or reading aloud) was measured using speech rate, percentage of interruptions, fundamental frequency (F0), and relative intensity. Results showed that (1) both DAF and FAF caused slower speech rates and more interruptions while reading aloud, with DAF having larger effect; (2) altered feedback produced no differences between groups, except an increase in F0 for CI users during DAF; and (3) CI users’ ability to understand speech via phone and without lip-reading was positively correlated with performance under DAF. These findings suggest that auditory perturbation similarly affects speech production among prelingual CI users and NH individuals, indicating CI users depend on auditory feedback to the same degree as normal hearing individuals.

We investigated the suitability of the gating task for studying the on-line process of spoken word recognition. To do this, we compared two different versions of the task. In one version, subjects were placed under no time constraints, and in the other, they were encouraged to respond as rapidly as possible. Target words occurred either in isolation or in various types of syntactic and semantic contexts. These different contexts had the same effect on word recognition whether subjects responded within 500 msec of fragment offset or without time constraints. We conclude that both versions of the task are as sensitive as other on-line tasks to the real-time processes involved in spoken word recognition.

Cochlear implants (CIs) restore speech perception in quiet but they also eliminate or distort many acoustic cues that are important for music enjoyment. Unfortunately, quantifying music enjoyment by CI users has been difficult because comparisons must rely on their recollection of music before they lost their hearing. Here, we aimed to assess music enjoyment in CI users using a readily interpretable reference based on acoustic hearing. The comparison was done by testing "single-sided deafness" (SSD) patients who have normal hearing (NH) in one ear and a CI in the other ear. The study also aimed to assess binaural musical enjoyment, with the reference being the experience of hearing with a single NH ear. Three experiments assessed the effect of adding different kinds of input to the second ear: electrical, vocoded, or unmodified. In experiment 1, music enjoyment in SSD-CI users was investigated using a modified version of the MUSHRA (MUltiple Stimuli with Hidden Reference and Anchor) method. Listeners rated their enjoyment of song segments on a scale of 0 to 200, where 100 represented the enjoyment obtained from a song segment presented to the NH ear, 0 represented a highly degraded version of the same song segment presented to the same ear, and 200 represented enjoyment subjectively rated as twice as good as the 100 reference. Stimuli consisted of acoustic only, electric only, acoustic and electric, as well as other conditions with low pass filtered acoustic stimuli. Acoustic stimulation was provided by headphone to the NH ear and electric stimulation was provided by direct audio input to the subject's speech processor. In experiment 2, the task was repeated using NH listeners who received vocoded stimuli instead of electric stimuli. Experiment 3 tested the effect of adding the same unmodified song segment to the second ear, also in NH listeners. Music presented through the CI only was very unpleasant, with an average rating of 20. Surprisingly, the combination of the unpleasant CI signal in one ear with acoustic stimulation in the other ear was rated more enjoyable (mean = 123) than acoustic processing alone. Presentation of the same monaural musical signal to both ears in NH listeners resulted with even greater enhancement of the experience compared with presentation to a single ear (mean = 159). Repeating the experiment using a vocoder to one ear of NH listeners resulted in interference rather than enhancement. Music enjoyment from electric stimulation is extremely poor relative to a readily interpretable NH baseline for CI-SSD listeners. However, the combination of this unenjoyable signal presented through a CI and an unmodified acoustic signal presented to a NH (or near-NH) contralateral ear results in enhanced music enjoyment with respect to the acoustic signal alone. Remarkably, this two-ear enhancement experienced by CI-SSD listeners represents a substantial fraction of the two-ear enhancement seen in NH listeners. This unexpected benefit of electroacoustic auditory stimulation will have to be considered in theoretical accounts of music enjoyment and may facilitate the quest to enhance music enjoyment in CI users.

A cochlear implant (CI) is a hearing device introduced in the 1980s for profoundly deaf subjects who gained little or no benefit from powerful hearing aids. This device comprises an electrode array inserted in the cochlea, connected to an internal receiver, and an externally worn speech processor. The CI transforms acoustic signals into electrical currents which directly stimulate the auditory nerve. Since the early 1990s, cochlear implantation in children has been developing rapidly. Although it is still difficult to predict how a child will perform with a cochlear implant, the success of cochlear implantation can no longer be denied. In this paper, some recent papers and reports, and the results of the various Nijmegen cochlear implant studies, are reviewed. Issues about selection, examinations, surgery and the outcome are discussed. Overall, our results were comparable with those of other authors. It can be concluded that cochlear implantation is an effective treatment for postlingually deaf as well as prelingually (congenital or acquired) deaf children with profound bilateral sensorineural deafness.

Auditory cortical activity to different voice onset times in cochlear implant users

Individuals with cochlear implants (CIs) show reduced word and auditory emotion recognition abilities relative to their peers with normal hearing. Modern CI processing strategies are designed to preserve acoustic cues requisite for word recognition rather than those cues required for accessing other signal information (e.g., talker gender or emotional state). While word recognition is undoubtedly important for communication, the inaccessibility of this additional signal information in speech may lead to negative social experiences and outcomes for individuals with hearing loss. This study aimed to evaluate whether the emphasis on word recognition preservation in CI processing has unintended consequences on the perception of other talker information, such as emotional state. Twenty-four young adult listeners with normal hearing listened to sentences and either reported a target word in each sentence (word recognition task) or selected the emotion of the talker (emotion recognition task) from a list of options (Angry, Calm, Happy, and Sad). Sentences were blocked by task type (emotion recognition versus word recognition) and processing condition (unprocessed versus 8-channel noise vocoder) and presented randomly within the block at three signal-to-noise ratios (SNRs) in a background of speech-shaped noise. Confusion matrices showed the number of errors in emotion recognition by listeners. Listeners demonstrated better emotion recognition performance than word recognition performance at the same SNR. Unprocessed speech resulted in higher recognition rates than vocoded stimuli. Recognition performance (for both words and emotions) decreased with worsening SNR. Vocoding speech resulted in a greater negative impact on emotion recognition than it did for word recognition. These data confirm prior work that suggests that in background noise, emotional prosodic information in speech is easier to recognize than word information, even after simulated CI processing. However, emotion recognition may be more negatively impacted by background noise and CI processing than word recognition. Future work could explore CI processing strategies that better encode prosodic information and investigate this effect in individuals with CIs as opposed to vocoded simulation. This study emphasized the need for clinicians to consider not only word recognition but also other aspects of speech that are critical to successful social communication.

On the relationship between auditory cognition and speech intelligibility in cochlear implant users: An ERP study

This study aimed to characterize horizontal plane sound localization in interfering noise at different signal-to-noise ratios (SNRs) and to compare performance across normal-hearing listeners and users of unilateral and bilateral cochlear implants (CIs). CI users report difficulties with listening in noisy environments. Although their difficulties with speech understanding have been investigated in several studies, the ability to localize sounds in background noise has not extensively been examined, despite the benefits of binaural hearing being greatest in noisy situations. Sound localization is a measure of binaural processing and is thus well suited to assessing the benefit of bilateral implantation. The results will inform clinicians and implant manufacturers how to focus their efforts to improve localization with CIs in noisy situations. Six normal-hearing listeners, four unilateral, and 10 bilateral CI users indicated the perceived location of sound sources using a light pointer method. Target sounds were noise pulses played from one of 11 loudspeakers placed between -80 and +80 degrees in the frontal horizontal plane in the free field. Localization was assessed in quiet and in diffuse background noise at SNRs between +10 and -7 dB. Speech reception thresholds were measured and their relation to the localization results examined. Localization performance declined with decreasing SNR: target sounds were perceived closer to the median plane and the standard deviation of responses increased. Localization performance across groups was compared using a measure of "Spatial Resolvability" (SR). This measure gives the angular separation between two sound sources that would enable an ideal observer to correctly distinguish them 69.1% of the time. For all participants SR increased with decreasing SNR, that is, at low SNRs the spatial separation between sound sources remained distinguishable only when it was larger. Normal-hearing participants performed best, with SR between 1.4 and 5.1 degrees in quiet. Bilateral CI users showed SR between 8.3 and 43.6 degrees in quiet, corresponding approximately to the spatial resolution of normal-hearing listeners at an SNR of -5 dB. Most bilateral CI users had lost the ability to correctly determine which side the sound came from at an SNR of -3 dB. Overall, the SNR had to be at least +7 dB to achieve localization performance near to that in quiet for all bilateral CI users. No significant correlation was found between spatial resolution and speech reception thresholds, but the speech processor sensitivity setting did significantly affect performance. Unilateral CI users showed the most severe localization problems, with only two of four participants being able to correctly determine which side sounds came from in quiet. This study is the first to examine sound localization with CIs at various SNRs and to compare it with normal hearing. The results confirm that localization with CIs is strongly disrupted in noisy situations. Bilateral CIs were shown to be clearly superior over unilateral CIs for localization in quiet and in noisy situations. With bilateral CIs, localization declined at moderately high absolute noise levels (>63 dB SPL), suggesting that an extension of the acoustic-dynamic range to higher levels would be beneficial. The absence of a relation between speech reception thresholds and spatial resolution highlights the need for additional clinical tests to assess the binaural benefit of a second implant.

Current postoperative clinical outcome measures for adults receiving cochlear implants (CIs) consist of testing speech recognition, primarily under quiet conditions. However, it is strongly suspected that results on these measures may not adequately reflect patients' quality of life (QOL) using their implants. This study aimed to evaluate whether QOL for CI users depends on speech recognition performance. Twenty-three postlingually deafened adults with CIs were assessed. Participants were tested for speech recognition (Central Institute for the Deaf word and AzBio sentence recognition in quiet) and completed three QOL measures-the Nijmegen Cochlear Implant Questionnaire; either the Hearing Handicap Inventory for Adults or the Hearing Handicap Inventory for the Elderly; and the Speech, Spatial and Qualities of Hearing Scale questionnaires-to assess a variety of QOL factors. Correlations were sought between speech recognition and QOL scores. Demographics, audiologic history, language, and cognitive skills were also examined as potential predictors of QOL. Only a few QOL scores significantly correlated with postoperative sentence or word recognition in quiet, and correlations were primarily isolated to speech-related subscales on QOL measures. Poorer pre- and postoperative unaided hearing predicted better QOL. Socioeconomic status, duration of deafness, age at implantation, duration of CI use, reading ability, vocabulary size, and cognitive status did not consistently predict QOL scores. For adult, postlingually deafened CI users, clinical speech recognition measures in quiet do not correlate broadly with QOL. Results suggest the need for additional outcome measures of the benefits and limitations of cochlear implantation. 4. Laryngoscope, 126:699-706, 2016.