Cortical Networks for Recognition of Speech with Simultaneous Talkers

The relative contributions of superior temporal (auditory) vs. inferior frontal and parietal (sensorimotor) networks to recognition of speech against competing speech remain unclear, although the contributions themselves are well established. Here, we use fMRI with spectrotemporal receptive field (STRF) modeling to examine the speech information represented in temporal vs. frontoparietal networks for two speech recognition tasks with and without a competing talker. We also generate ‘neurometric functions’ that describe the relative contributions of these networks to speech recognition performance. Specifically, 25 listeners completed two versions of a 3-Alternative Forced-Choice (3-AFC) competing speech task: “Unison” and “Competing”, in which a female (target) and a male (competing) talker uttered identical or different phrases, respectively. Spectrotemporal modulation filtering was applied to the two-talker mixtures and a “boosting” procedure was used to generate STRF models to predict brain activation from differences in spectrotemporal distortion on each trial. STRF model predictive accuracy was better for Competing than Unison in a bilateral temporal lobe network, and better for Unison than Competing in a large network of frontoparietal and midline brain regions. Agglomerative STRF clustering further revealed three subnetworks: a bilateral superior temporal Intelligibility network, a frontoparietal Distortion network, and a Semantic network distributed across classic semantic memory regions. The Intelligibility and Semantic networks responded primarily to spectrotemporal cues associated with speech intelligibility, regardless of condition, while the Distortion network responded to the absence of such cues in both conditions, but also to the absence (presence) of target-talker (competing-talker) vocal pitch in the Competing condition, suggesting a generalized response to signal degradation. Neurometric function analysis showed that: (i) activation in the Intelligibility network was strongly positively correlated with behavioral performance and that this relation was entirely STRF-mediated; and (ii) activation in the Distortion network was strongly negatively correlated with performance and this relation was only partially STRF-mediated. The contributions to performance from these networks were partially independent and of roughly equal magnitude. Finally, activation in the Semantic network was weakly positively correlated with performance and this relation was entirely superseded by those in the Intelligibility and Distortion networks. We conclude: (a) superior temporal regions play a bottom-up, perceptual role in competing speech tasks; (b) frontoparietal regions play a top-down, task-dependent role in competing speech tasks that scales with listening effort; and (c) performance ultimately relies on dynamic interactions between these networks, with additional contributions from semantic regions that likely scale with the semantic predictability of the speech material.

Speech Understanding in Modulated Noise and Speech Maskers as a Function of Cognitive Status in Older Adults

Objectives The purpose of this study was to investigate the impact of different types of maskers on speech understanding as a function of cognitive status in older adults. The hypothesis tested was that individuals with a diagnosis of mild cognitive impairment (MCI) or mild dementia would perform like their age- and hearing status–matched control counterparts in modulated noise but would perform more poorly in the presence of competing speech. Design Participants ( n = 39; age range: 55–77 years old) performed a speech-in-noise task and completed two cognitive screening tests and a measure of working memory. Sentences were presented in the presence of two types of maskers (i.e., speech envelope–modulated noise and two-talker, same-sex competing speech). Two analyses were undertaken: (a) a between-groups comparison of individuals diagnosed with MCI/dementia, individuals who failed both cognitive screeners (possible MCI), and age- and hearing status–matched neurologically healthy control individuals and (b) a mixed-model analysis of variance of speech perception performance as a function of working memory capacity. Results The between-groups comparison yielded significant group differences for speech understanding in both masking conditions, with the MCI/dementia group performing more poorly than the neurologically healthy controls and possible MCI groups. A single measure of working memory (Size Comparison Span [SICSPAN]) was correlated with performance on the speech perception task in the competing speech conditions. Conclusions Adults with a diagnosis of MCI or mild dementia performed more poorly on a speech perception task than their age- and hearing status–matched control counterparts in the presence of both maskers, with larger group mean differences when the target speech was presented in a two-talker masker. This suggests increased difficulty understanding speech in the presence of distracting backgrounds for people with MCI/dementia. Future studies should consider how to target this potentially vulnerable population as they may be experiencing increased difficulty communicating in challenging environments.

Speech Recognition With Informational and Energetic Maskers in Patients With Single-Sided Deafness After Cochlear Implantation

Purpose The aim of the study was to assess the susceptibility to energetic and informational masking in patients with single-sided deafness (SSD) with one normal-hearing (NH) ear and a cochlear implant (CI) in the contralateral ear, understand the effect on speech recognition when spatially separating noise and speech maskers, and investigate the influence of the CI in situations with energetic and informational masking. Method Speech recognition was measured in the presence of either a modulated speech-shaped noise or one of two competing speech maskers in 11 SSD-CI listeners. The speech maskers were manipulated with respect to fundamental frequency to consider the effect of different voices. Measurements were conducted in the unaided (NH) and aided (NHCI) conditions. Spatial release from masking (SRM) was calculated for each masker type and both listening conditions (NH and NHCI) by subtracting scores of the colocated target and masker condition (S 0 N 0 ) from the spatially separated target and masker conditions (S 0 N ≠0 ). Results Speech recognition was highly variable depending on the type of masker. SRM occurred in the unaided (NH) and aided (NHCI) conditions when the speech masker had the same gender as the target talker. Adding the CI improved speech recognition when this speech masker was ipsilateral to the NH ear. Conclusions The amount of informational masking is substantial in SSD-CI listeners with both colocated and spatially separated target and masker signals. The contribution of SRM to better speech recognition largely depends on the masker and is considerable when no differences in voices between the target and the competing talker occur. There is only a slight improvement in speech recognition by adding the CI.

Aging Effect on Mandarin Chinese Vowel and Tone Identification in Six-Talker Babble

Purpose The purpose of this study was to measure Mandarin Chinese vowel-plus-tone identification in quiet and noise for younger and older listeners. Method Two types of noise served as the masker, namely, six-talker babble and babble-modulated noise, at two signal-to-noise ratios (SNRs) of −4 and −8 dB. Fourteen listeners from both age groups were recruited, and three sets of data analyses were conducted: the identification of vowel plus tone, the identification of vowel, and the identification of tone. Results Younger listeners outperformed older listeners in all listening conditions, whereas the younger–older listener difference became greater in noise than in quiet, indicating a more detrimental effect of noise for older listeners than for younger listeners. In addition, vowel identification showed slightly better scores than tone identification in noise, suggesting that noise appeared to affect tone perception more negatively than vowel perception in Mandarin Chinese. At −4 dB SNR, there was a significantly greater amount of informational masking (IM) and a greater amount of energetic masking (EM) for older listeners than for younger listeners. At −8 dB SNR, there was a greater amount of EM for older listeners than for younger listeners but with no group difference in the amount of IM. Conclusion These results suggest that older listeners received a more negative impact of noise for Mandarin Chinese phonemic and tone recognition and had a larger amount of IM or EM from competing speech noise than younger listeners, depending on the SNR.