Attenuation and distortion components of age-related hearing loss: Contributions to recognizing temporal-envelope filtered speech in modulated noise.

Older adults with hearing loss may experience difficulty recognizing speech in noise due to factors related to attenuation (e.g., reduced audibility and sensation levels, SLs) and distortion (e.g., reduced temporal fine structure, TFS, processing). Furthermore, speech recognition may improve when the amplitude modulation spectrum of the speech and masker are non-overlapping. The current study investigated this by filtering the amplitude modulation spectrum into different modulation rates for speech and speech-modulated noise. The modulation depth of the noise was manipulated to vary the SL of speech glimpses. Younger adults with normal hearing and older adults with normal or impaired hearing listened to natural speech or speech vocoded to degrade TFS cues. Control groups of younger adults were tested on all conditions with spectrally shaped speech and threshold matching noise, which reduced audibility to match that of the older hearing-impaired group. All groups benefitted from increased masker modulation depth and preservation of syllabic-rate speech modulations. Older adults with hearing loss had reduced speech recognition across all conditions. This was explained by factors related to attenuation, due to reduced SLs, and distortion, due to reduced TFS processing, which resulted in poorer auditory processing of speech cues during the dips of the masker.

Atypical vocal quality in women with the FMR1 premutation: an indicator of impaired sensorimotor control.

Women with the FMR1 premutation are susceptible to motor involvement related to atypical cerebellar function, including risk for developing fragile X tremor ataxia syndrome. Vocal quality analyses are sensitive to subtle differences in motor skills but have not yet been applied to the FMR1 premutation. This study examined whether women with the FMR1 premutation demonstrate differences in vocal quality, and whether such differences relate to FMR1 genetic, executive, motor, or health features of the FMR1 premutation. Participants included 35 women with the FMR1 premutation and 45 age-matched women without the FMR1 premutation who served as a comparison group. Three sustained /a/ vowels were analyzed for pitch (mean F0), variability of pitch (standard deviation of F0), and overall vocal quality (jitter, shimmer, and harmonics-to-noise ratio). Executive, motor, and health indices were obtained from direct and self-report measures and genetic samples were analyzed for FMR1 CGG repeat length and activation ratio. Women with the FMR1 premutation had a lower pitch, larger pitch variability, and poorer vocal quality than the comparison group. Working memory was related to harmonics-to-noise ratio and shimmer in women with the FMR1 premutation. Vocal quality abnormalities differentiated women with the FMR1 premutation from the comparison group and were evident even in the absence of other clinically evident motor deficits. This study supports vocal quality analyses as a tool that may prove useful in the detection of early signs of motor involvement in this population.

Sentence recognition with modulation-filtered speech segments for younger and older adults: Effects of hearing impairment and cognition.

This study investigated word recognition for sentences temporally filtered within and across acoustic-phonetic segments providing primarily vocalic or consonantal cues. Amplitude modulation was filtered at syllabic (0-8 Hz) or slow phonemic (8-16 Hz) rates. Sentence-level modulation properties were also varied by amplifying or attenuating segments. Participants were older adults with normal or impaired hearing. Older adult speech recognition was compared to groups of younger normal-hearing adults who heard speech unmodified or spectrally shaped with and without threshold matching noise that matched audibility to hearing-impaired thresholds. Participants also completed cognitive and speech recognition measures. Overall, results confirm the primary contribution of syllabic speech modulations to recognition and demonstrate the importance of these modulations across vowel and consonant segments. Group differences demonstrated a hearing loss-related impairment in processing modulation-filtered speech, particularly at 8-16 Hz. This impairment could not be fully explained by age or poorer audibility. Principal components analysis identified a single factor score that summarized speech recognition across modulation-filtered conditions; analysis of individual differences explained 81% of the variance in this summary factor among the older adults with hearing loss. These results suggest that a combination of cognitive abilities and speech glimpsing abilities contribute to speech recognition in this group.

Phonological and semantic similarity of misperceived words in babble: Effects of sentence context, age, and hearing loss.

This study investigated how age and hearing loss influence the misperceptions made when listening to sentences in babble. Open-set responses to final words in sentences with low and high context were analyzed for younger adults with normal hearing and older adults with normal or impaired hearing. All groups performed similarly in overall accuracy but differed in error type. Misperceptions for all groups were analyzed according to phonological and semantic properties. Comparisons between groups indicated that misperceptions for older adults were more influenced by phonological factors. Furthermore, older adults with hearing loss omitted more responses. Overall, across all groups, results suggest that phonological confusions most explain misperceptions in low context sentences. In high context sentences, the meaningful sentence context appears to provide predictive cues that reduce misperceptions. When misperceptions do occur, responses tend to have greater semantic similarity and lesser phonological similarity to the target, compared to low context sentences. In this way, semantic similarity may index a postdictive process by which ambiguities due to phonological confusions are resolved to conform to the semantic context of the sentence. These patterns demonstrate that context, age, and hearing loss affect the misperceptions, and potential sentence interpretation, made when listening to sentences in babble.

Older adult recognition error patterns when listening to interrupted speech and speech in steady-state noise.

This study examined sentence recognition errors made by older adults in degraded listening conditions compared to a previous sample of younger adults. We examined speech recognition errors made by older normal-hearing adults who repeated sentences that were corrupted by steady-state noise (SSN) or periodically interrupted by noise to preserve 33%, 50%, or 66% of the sentence. Responses were transcribed and coded for the number and type of keyword errors. Errors increased with decreasing preservation of the sentence. Similar sentence recognition was observed between SSN and the greatest amount of interruption (33%). Errors were predominately at the word level rather than at the phoneme level and consisted of omission or substitution of keywords. Compared to younger listeners, older listeners made more total errors and omitted more whole words when speech was highly degraded. They also made more whole word substitutions when speech was more preserved. In addition, the semantic relatedness of the substitution errors to the sentence context varied according to the distortion condition, with greater context effects in SSN than interruption. Overall, older listeners made errors reflecting poorer speech representations. Error analyses provide a more detailed account of speech recognition by identifying changes in the type of errors made across listening conditions and listener groups.

Glimpsing keywords across sentences in noise: A microstructural analysis of acoustic, lexical, and listener factors.

This study investigated how acoustic and lexical word-level factors and listener-level factors of auditory thresholds and cognitive-linguistic processing contribute to the microstructure of sentence recognition in unmodulated and speech-modulated noise. The modulation depth of the modulated masker was changed by expanding and compressing the temporal envelope to control glimpsing opportunities. Younger adults with normal hearing (YNH) and older adults with normal and impaired hearing were tested. A second group of YNH was tested under acoustically identical conditions to the hearing-impaired group, who received spectral shaping. For all of the groups, speech recognition declined and masking release increased for later keywords in the sentence, which is consistent with the word position decreases in the signal-to-noise ratio. The acoustic glimpse proportion and lexical word frequency of individual keywords predicted recognition under different noise conditions. For the older adults, better auditory thresholds and better working memory abilities facilitated sentence recognition. Vocabulary knowledge contributed more to sentence recognition for younger than for older adults. These results demonstrate that acoustic and lexical factors contribute to the recognition of individual words within a sentence, but relative contributions vary based on the noise modulation characteristics. Taken together, acoustic, lexical, and listener factors contribute to how individuals recognize keywords during sentences.

Probing Phonological Processing Differences in Nonword Repetition for Children with Separate or Co-occurring Dyslexia and Developmental Language Disorder.

We assessed nonword repetition (NWR) skills in 7-9 year-old children with dyslexia (dyslexia-only), developmental language disorder (DLD-only), co-occurring DLD+dyslexia, and typical development (TD) with a norm-referenced and an experimental task. The experimental task manipulated phonemic variability (dissimilarity among consonant phonemes within the nonword) and presentation modality (audio-only versus audiovisual) to probe potential phonological processing differences among the groups. Across tasks, the dyslexia-only and DLD-only groups performed similarly to each other and intermediately to the TD and DLD+dyslexia groups. In the experimental task, nonwords with low phonemic variability were produced less accurately in both modalities, and audiovisual presentation facilitated accurate repetition of low phonemic variability nonwords. A lack of a group interaction with phonemic variability or presentation modality suggests similarities, despite group differences, in how underlying phonological representations influence task performance. Overall, results suggest that poor NWR is associated with both dyslexia and DLD, and that co-occurrence compounds this difficulty.

Combining partial information from speech and text.

The current study investigated how partial speech and text information, distributed at various interruption rates, is combined to support sentence recognition in quiet. Speech and text stimuli were interrupted by silence and presented unimodally or combined in multimodal conditions. Across all conditions, performance was best at the highest interruption rates. Listeners were able to gain benefit from most multimodal presentations, even when the rate of interruption was mismatched between modalities. Supplementing partial speech with incomplete visual cues can improve sentence intelligibility and compensate for degraded speech in adverse listening conditions. However, individual variability in benefit depends on unimodal performance.

The effect of simulated room acoustic parameters on the intelligibility and perceived reverberation of monosyllabic words and sentences.

Individual acoustic parameters of reverberation have the potential to affect both the intelligibility of speech and the degree of perceived reverberation. The current experiments used monaural acoustic simulations to investigate the effect of reverberation time (RT) and direct-to-reverberant ratio (DRR) on word and sentence intelligibility at different levels of analysis (phonemes, words, and sentences). Perceived reverberation and recall of sentences were also assessed. Intelligibility and perceived reverberation decreased with increasing RT and decreasing DRR (particularly between 0 and -10 dB). Results indicate consistent effects of both RT and DRR on the intelligibility and perceived reverberation of words and sentences.

Spectro-temporal glimpsing of speech in noise: Regularity and coherence of masking patterns reduces uncertainty and increases intelligibility.

Adverse listening conditions involve glimpses of spectro-temporal speech information. This study investigated if the acoustic organization of the spectro-temporal masking pattern affects speech glimpsing in "checkerboard" noise. The regularity and coherence of the masking pattern was varied. Regularity was reduced by randomizing the spectral or temporal gating of the masking noise. Coherence involved the spectral alignment of frequency bands across time or the temporal alignment of gated onsets/offsets across frequency bands. Experiment 1 investigated the effect of spectral or temporal coherence. Experiment 2 investigated independent and combined factors of regularity and coherence. Performance was best in spectro-temporally modulated noise having larger glimpses. Generally, performance also improved as the regularity and coherence of masker fluctuations increased, with regularity having a stronger effect than coherence. An acoustic glimpsing model suggested that the effect of regularity (but not coherence) could be partially attributed to the availability of glimpses retained after energetic masking. Performance tended to be better with maskers that were spectrally coherent as compared to temporally coherent. Overall, performance was best when the spectro-temporal masking pattern imposed even spectral sampling and minimal temporal uncertainty, indicating that listeners use reliable masking patterns to aid in spectro-temporal speech glimpsing.

Explaining intelligibility in speech-modulated maskers using acoustic glimpse analysis.

Intelligibility was measured in speech-modulated noise varying in level and temporal modulation rate (TMR). Acoustic analysis measured glimpses available above a local signal-to-noise ratio criterion (LC). The proportion and rate of glimpses were correlated with intelligibility, particularly in relation to masker level or TMR manipulations, respectively. Intelligibility correlations for each metric were maximized at different analysis LCs. Regression analysis showed that both metrics measured at -2 dB LC were required to best explain the total variance (R2 = 0.49) for individual sentence intelligibility. Acoustic conditions associated with recognizing speech in complex maskers are best explained using multidimensional glimpse metrics.

Glimpsing speech in temporally and spectro-temporally modulated noise.

Speech recognition in fluctuating maskers is influenced by the spectro-temporal properties of the noise. Three experiments examined different temporal and spectro-temporal noise properties. Experiment 1 replicated previous work by highlighting maximum performance at a temporal gating rate of 4-8 Hz. Experiment 2 involved spectro-temporal glimpses. Performance was best with the largest glimpses, and performance with small glimpses approached that for continuous noise matched to the average level of the modulated noise. Better performance occurred with periodic than for random spectro-temporal glimpses. Finally, time and frequency for spectro-temporal glimpses were dissociated in experiment 3. Larger spectral glimpses were more beneficial than smaller, and minimum performance was observed at a gating rate of 4-8 Hz. The current results involving continuous speech in gated noise (slower and larger glimpses most advantageous) run counter to several results involving gated and/or filtered speech, where a larger number of smaller speech samples is often advantageous. This is because mechanisms of masking dominate, negating the advantages of better speech-information sampling. It is suggested that spectro-temporal glimpsing combines temporal glimpsing with additional processes of simultaneous masking and uncomodulation, and continuous speech in gated noise is a better model for real-world glimpsing than is gated and/or filtered speech.

Glimpsing speech interrupted by speech-modulated noise.

Everyday environments frequently present speech in modulated noise backgrounds, such as from a competing talker. Under such conditions, temporal glimpses of speech may be preserved at favorable signal-to-noise ratios during the amplitude dips of the masker. Speech recognition is determined, in part, by these speech glimpses. However, properties of the noise when it dominates the speech may also be important. This study interrupted speech to provide either high-intensity or low-intensity speech glimpses derived from measurements of speech-on-speech masking. These interrupted intervals were deleted and subsequently filled by steady-state noise or one of four different types of noise amplitude modulated by the same or different sentence. Noise was presented at two different levels. Interruption by silence was also examined. Speech recognition was best with high-intensity glimpses and improved when the noise was modulated by missing high-intensity segments. Additional noise conditions detailed significant interactions between the noise level and glimpsed speech level. Overall, high-intensity speech segments, and the amplitude modulation (AM) of the segments, are crucial for speech recognition. Speech recognition is further influenced by the properties of the competing noise (i.e., level and AM) which interact with the glimpsed speech level. Acoustic properties of both speech-dominated and noise-dominated intervals of speech-noise mixtures determine speech recognition.

Speech recognition error patterns for steady-state noise and interrupted speech.

Listening in various types of adverse listening conditions may lead to different errors in speech recognition. Young adults repeated sentences degraded by steady-state noise or periodically interrupted by noise preserved at varying proportions. Recognition errors were analyzed according to the noise type and speech proportion. Across noise types, as word recognition decreased, the occurrence of phonemic substitutions and whole word omissions increased. Listeners made more whole word omission and substitution errors during steady-state noise. Part word errors occurred most frequently when listening to speech presented in steady-state noise or interrupted by noise with the smallest speech proportion preserved.

Simultaneous and forward masking of vowels and stop consonants: Effects of age, hearing loss, and spectral shaping.

Fluctuating noise, common in everyday environments, has the potential to mask acoustic cues important for speech recognition. This study examined the extent to which acoustic cues for perception of vowels and stop consonants differ in their susceptibility to simultaneous and forward masking. Younger normal-hearing, older normal-hearing, and older hearing-impaired adults identified initial and final consonants or vowels in noise-masked syllables that had been spectrally shaped. The amount of shaping was determined by subjects' audiometric thresholds. A second group of younger adults with normal hearing was tested with spectral shaping determined by the mean audiogram of the hearing-impaired group. Stimulus timing ensured that the final 10, 40, or 100 ms of the syllable occurred after the masker offset. Results demonstrated that participants benefited from short temporal delays between the noise and speech for vowel identification, but required longer delays for stop consonant identification. Older adults with normal and impaired hearing, with sufficient audibility, required longer delays to obtain performance equivalent to that of the younger adults. Overall, these results demonstrate that in forward masking conditions, younger listeners can successfully identify vowels during short temporal intervals (i.e., one unmasked pitch period), with longer durations required for consonants and for older adults.

The Role of Fundamental Frequency and Temporal Envelope in Processing Sentences with Temporary Syntactic Ambiguities.

Previous experiments have demonstrated the impact of speech prosody on syntactic processing. The present study was designed to examine how listeners use specific acoustic properties of prosody for grammatical interpretation. We investigated the independent contributions of two acoustic properties associated with the pitch and rhythmic properties of speech; the fundamental frequency and temporal envelope, respectively. The effect of degrading these prosodic components was examined by testing listeners' ability to parse early-closure garden-path sentences. A second aim was to investigate how effects of prosody interact with semantic effects of sentence plausibility. Using a task that required both a comprehension and a production response, we were able to determine that degradation of the speech envelope more consistently affects syntactic processing than degradation of the fundamental frequency. These effects are exacerbated in sentences with plausible misinterpretations, showing that prosodic degradation interacts with contextual cues to sentence interpretation.

Speech recognition interference by the temporal and spectral properties of a single competing talker.

This study investigated how speech recognition during speech-on-speech masking may be impaired due to the interaction between amplitude modulations of the target and competing talker. Young normal-hearing adults were tested in a competing talker paradigm where the target and/or competing talker was processed to primarily preserve amplitude modulation cues. Effects of talker sex and linguistic interference were also examined. Results suggest that performance patterns for natural speech-on-speech conditions are largely consistent with the same masking patterns observed for signals primarily limited to temporal amplitude modulations. However, results also suggest a role for spectral cues in talker segregation and linguistic competition.

Integration of partial information for spoken and written sentence recognition by older listeners.

Older adults have difficulty understanding speech in challenging listening environments. Combining multisensory signals may facilitate speech recognition. This study measured recognition of interrupted spoken and written sentences by older adults for different preserved stimulus proportions. Unimodal performance was first examined when only interrupted text or speech stimuli were presented. Multimodal performance with concurrently presented text and speech stimuli was tested with delayed and simultaneous participant responses. Older listeners performed better in unimodal speech-only compared to text-only conditions across all proportions preserved. Performance was also better in delayed multimodal conditions. Comparison to a younger sample suggests age-related amodal processing declines.

Modulation masking and glimpsing of natural and vocoded speech during single-talker modulated noise: Effect of the modulation spectrum.

Compared to notionally steady-state noise, modulated maskers provide a perceptual benefit for speech recognition, in part due to preserved speech information during the amplitude dips of the masker. However, overlap in the modulation spectrum between the target speech and the competing modulated masker may potentially result in modulation masking, and thereby offset the release from energetic masking. The current study investigated masking release provided by single-talker modulated noise. The overlap in the modulation spectra of the target speech and the modulated noise masker was varied through time compression or expansion of the competing masker. Younger normal hearing adults listened to sentences that were unprocessed or noise vocoded to primarily limit speech recognition to the preserved temporal envelope cues. For unprocessed speech, results demonstrated improved performance with masker modulation spectrum shifted up or down compared to the target modulation spectrum, except for the most extreme time expansion. For vocoded speech, significant masking release was observed with the slowest masker rate. Perceptual results combined with acoustic analyses of the preserved glimpses of the target speech suggest contributions of modulation masking and cognitive-linguistic processing as factors contributing to performance.

Level considerations for chimeric processing: Temporal envelope and fine structure contributions to speech intelligibility.

Chimeric processing is used to assess the respective role of the acoustic temporal envelope (ENV) and the temporal fine structure (TFS) by adding noise to either component. An acoustic analysis demonstrates that adding noise to the ENV results in noise degradation of the ENV and overall signal attenuation, whereas adding noise to the TFS results in only noise degradation of the TFS. Young normal hearing adults were then tested using a modified chimeric strategy to maintain speech levels. Results partially confirm the primary role of the ENV in determining speech intelligibility but demonstrate significant TFS contributions during selective ENV masking.