The Effort of Repairing a Misperceived Word Can Impair Perception of Following Words, Especially for Listeners With Cochlear Implants.

OBJECTIVES: In clinical and laboratory settings, speech recognition is typically assessed in a way that cannot distinguish accurate auditory perception from misperception that was mentally repaired or inferred from context. Previous work showed that the process of repairing misperceptions elicits greater listening effort, and that this elevated effort lingers well after the sentence is heard. That result suggests that cognitive repair strategies might appear successful when testing a single utterance but fail for everyday continuous conversational speech. The present study tested the hypothesis that the effort of repairing misperceptions has the consequence of carrying over to interfere with perception of later words after the sentence. DESIGN: Stimuli were open-set coherent sentences that were presented intact or with a word early in the sentence replaced with noise, forcing the listener to use later context to mentally repair the missing word. Sentences were immediately followed by digit triplets, which served to probe carryover effort from the sentence. Control conditions allowed for the comparison to intact sentences that did not demand mental repair, as well as to listening conditions that removed the need to attend to the post-sentence stimuli, or removed the post-sentence digits altogether. Intelligibility scores for the sentences and digits were accompanied by time-series measurements of pupil dilation to assess cognitive load during the task, as well as subjective rating of effort. Participants included adults with cochlear implants (CIs), as well as an age-matched group and a younger group of listeners with typical hearing for comparison. RESULTS: For the CI group, needing to repair a missing word during a sentence resulted in more errors on the digits after the sentence, especially when the repair process did not result in a coherent sensible perception. Sentences that needed repair also contained more errors on the words that were unmasked. All groups showed substantial increase of pupil dilation when sentences required repair, even when the repair was successful. Younger typical hearing listeners showed clear differences in moment-to-moment allocation of effort in the different conditions, while the other groups did not. CONCLUSIONS: For CI listeners, the effort of needing to repair misperceptions in a sentence can last long enough to interfere with words that follow the sentence. This pattern could pose a serious problem for regular communication but would go overlooked in typical testing with single utterances, where a listener has a chance to repair misperceptions before responding. Carryover effort was not predictable by basic intelligibility scores, but can be revealed in behavioral data when sentences are followed immediately by extra probe words such as digits.

How to vocode: Using channel vocoders for cochlear-implant research.

The channel vocoder has become a useful tool to understand the impact of specific forms of auditory degradation-particularly the spectral and temporal degradation that reflect cochlear-implant processing. Vocoders have many parameters that allow researchers to answer questions about cochlear-implant processing in ways that overcome some logistical complications of controlling for factors in individual cochlear implant users. However, there is such a large variety in the implementation of vocoders that the term "vocoder" is not specific enough to describe the signal processing used in these experiments. Misunderstanding vocoder parameters can result in experimental confounds or unexpected stimulus distortions. This paper highlights the signal processing parameters that should be specified when describing vocoder construction. The paper also provides guidance on how to determine vocoder parameters within perception experiments, given the experimenter's goals and research questions, to avoid common signal processing mistakes. Throughout, we will assume that experimenters are interested in vocoders with the specific goal of better understanding cochlear implants.

A Large-Scale Study of the Relationship Between Degree and Type of Hearing Loss and Recognition of Speech in Quiet and Noise.

OBJECTIVES: Understanding speech in noise (SIN) is the dominant complaint of individuals with hearing loss. For decades, the default test of speech perception in routine audiologic assessment has been monosyllabic word recognition in quiet (WRQ), which does not directly address patient concerns, leading some to advocate that measures of SIN should be integrated into routine practice. However, very little is known with regard to how SIN abilities are affected by different types of hearing loss. Here, we examine performance on clinical measures of WRQ and SIN in a large patient base consisting of a variety of hearing loss types, including conductive (CHL), mixed (MHL), and sensorineural (SNHL) losses. DESIGN: In a retrospective study, we examined data from 5593 patients (51% female) who underwent audiometric assessment at the Stanford Ear Institute. All individuals completed pure-tone audiometry, and speech perception testing of monaural WRQ, and monaural QuickSIN. Patient ages ranged from 18 to 104 years (average = 57). The average age in years for the different classifications of hearing loss was 51.1 (NH), 48.5 (CHL), 64.2 (MHL), and 68.5 (SNHL), respectively. Generalized linear mixed-effect models and quartile regression were used to determine the relationship between hearing loss type and severity for the different speech-recognition outcome measures. RESULTS: Patients with CHL had similar performance to patients with normal hearing on both WRQ and QuickSIN, regardless of the hearing loss severity. In patients with MHL or SNHL, WRQ scores remained largely excellent with increasing hearing loss until the loss was moderately severe or worse. In contrast, QuickSIN signal to noise ratio (SNR) losses showed an orderly systematic decrease as the degree of hearing loss became more severe. This effect scaled with the data, with threshold-QuickSIN relationships absent for CHL, and becoming increasingly stronger for MHL and strongest in patients with SNHL. However, the variability in these data suggests that only 57% of the variance in WRQ scores, and 50% of the variance in QuickSIN SNR losses, could be accounted for by the audiometric thresholds. Patients who would not be differentiated by WRQ scores are shown to be potentially differentiable by SIN scores. CONCLUSIONS: In this data set, conductive hearing loss had little effect on WRQ scores or QuickSIN SNR losses. However, for patients with MHL or SNHL, speech perception abilities decreased as the severity of the hearing loss increased. In these data, QuickSIN SNR losses showed deficits in performance with degrees of hearing loss that yielded largely excellent WRQ scores. However, the considerable variability in the data suggests that even after classifying patients according to their type of hearing loss, hearing thresholds only account for a portion of the variance in speech perception abilities, particularly in noise. These results are consistent with the idea that variables such as cochlear health and aging add explanatory power over audibility alone.