Using auditory pre-information to solve the cocktail-party problem: electrophysiological evidence for age-specific differences

Simultaneous relative cue reliance in speech-on-speech masking

Modern hearing research has identified the ability of listeners to segregate simultaneous speech streams with a reliance on three major voice cues, fundamental frequency, level, and location. Few of these studies evaluated reliance for these cues presented simultaneously as occurs in nature, and fewer still considered the listeners' relative reliance on these cues owing to the cues' different units of measure. In the present study trial-by-trial analyses were used to isolate the listener's simultaneous reliance on the three voice cues, with the behavior of an ideal observer [Green and Swets (1966). (Wiley, New York), pp.151-178] serving as a comparison standard for evaluating relative reliance. Listeners heard on each trial a pair of randomly selected, simultaneous recordings of naturally spoken sentences. One of the recordings was always from the same talker, a distracter, and the other, with equal probability, was from one of two target talkers differing in the three voice cues. The listener's task was to identify the target talker. Among 33 clinically normal-hearing adults only one relied predominantly on voice level, the remaining were split between voice fundamental frequency and/or location. The results are discussed regarding their implications for the common practice in studies of using target-distracter level as a dependent measure of speech-on-speech masking.

Selective spatial attention in lateralized multi-talker speech perception: EEG correlates and the role of age

Speech comprehension under dynamic cocktail party conditions requires auditory search for relevant speech content and focusing spatial attention on the target talker. Here, we investigated the development of these cognitive processes in a population of 329 participants aged 20-70 years. We used a multi-talker speech detection and perception task in which pairs of words (each consisting of a cue and a target word) were simultaneously presented from lateralized positions. Participants attended to predefined cue words and responded to the corresponding target. Task difficulty was varied by presenting cue and target stimuli at different intensity levels. Decline in performance was observed only in the oldest group (age range 53-70 years) and only in the most difficult condition. The EEG analysis of neurocognitive correlates of lateralized auditory attention and stimulus evaluation (N2ac, LPCpc, alpha power lateralization) revealed age-associated changes in focussing on and processing of task-relevant information, while no such deficits were found on early auditory search and target segregation. Irrespective of age, more challenging listening conditions were associated with an increased allocation of attentional resources.

Lexical Effects on the Perceived Clarity of Noise-Vocoded Speech in Younger and Older Listeners

When listening to degraded speech, such as speech delivered by a cochlear implant (CI), listeners make use of top-down linguistic knowledge to facilitate speech recognition. Lexical knowledge supports speech recognition and enhances the perceived clarity of speech. Yet, the extent to which lexical knowledge can be used to effectively compensate for degraded input may depend on the degree of degradation and the listener's age. The current study investigated lexical effects in the compensation for speech that was degraded via noise-vocoding in younger and older listeners. In an online experiment, younger and older normal-hearing (NH) listeners rated the clarity of noise-vocoded sentences on a scale from 1 ("very unclear") to 7 ("completely clear"). Lexical information was provided by matching text primes and the lexical content of the target utterance. Half of the sentences were preceded by a matching text prime, while half were preceded by a non-matching prime. Each sentence also consisted of three key words of high or low lexical frequency and neighborhood density. Sentences were processed to simulate CI hearing, using an eight-channel noise vocoder with varying filter slopes. Results showed that lexical information impacted the perceived clarity of noise-vocoded speech. Noise-vocoded speech was perceived as clearer when preceded by a matching prime, and when sentences included key words with high lexical frequency and low neighborhood density. However, the strength of the lexical effects depended on the level of degradation. Matching text primes had a greater impact for speech with poorer spectral resolution, but lexical content had a smaller impact for speech with poorer spectral resolution. Finally, lexical information appeared to benefit both younger and older listeners. Findings demonstrate that lexical knowledge can be employed by younger and older listeners in cognitive compensation during the processing of noise-vocoded speech. However, lexical content may not be as reliable when the signal is highly degraded. Clinical implications are that for adult CI users, lexical knowledge might be used to compensate for the degraded speech signal, regardless of age, but some CI users may be hindered by a relatively poor signal.

The Listener Effect in Multitalker Speech Segregation and Talker Identification

Over six decades ago, Cherry (1953) drew attention to what he called the “cocktail-party problem”; the challenge of segregating the speech of one talker from others speaking at the same time. The problem has been actively researched ever since but for all this time one observation has eluded explanation. It is the wide variation in performance of individual listeners. That variation was replicated here for four major experimental factors known to impact performance: differences in task (talker segregation vs. identification), differences in the voice features of talkers (pitch vs. location), differences in the voice similarity and uncertainty of talkers (informational masking), and the presence or absence of linguistic cues. The effect of these factors on the segregation of naturally spoken sentences and synthesized vowels was largely eliminated in psychometric functions relating the performance of individual listeners to that of an ideal observer, d′_ideal. The effect of listeners remained as differences in the slopes of the functions (fixed effect) with little within-listener variability in the estimates of slope (random effect). The results make a case for considering the listener a factor in multitalker segregation and identification equal in status to any major experimental variable.

Short-Term Audiovisual Spatial Training Enhances Electrophysiological Correlates of Auditory Selective Spatial Attention

Audiovisual cross-modal training has been proposed as a tool to improve human spatial hearing. Here, we investigated training-induced modulations of event-related potential (ERP) components that have been associated with processes of auditory selective spatial attention when a speaker of interest has to be localized in a multiple speaker ("cocktail-party") scenario. Forty-five healthy participants were tested, including younger (19-29 years; n = 21) and older (66-76 years; n = 24) age groups. Three conditions of short-term training (duration 15 min) were compared, requiring localization of non-speech targets under "cocktail-party" conditions with either (1) synchronous presentation of co-localized auditory-target and visual stimuli (audiovisual-congruency training) or (2) immediate visual feedback on correct or incorrect localization responses (visual-feedback training), or (3) presentation of spatially incongruent auditory-target and visual stimuli presented at random positions with synchronous onset (control condition). Prior to and after training, participants were tested in an auditory spatial attention task (15 min), requiring localization of a predefined spoken word out of three distractor words, which were presented with synchronous stimulus onset from different positions. Peaks of ERP components were analyzed with a specific focus on the N2, which is known to be a correlate of auditory selective spatial attention. N2 amplitudes were significantly larger after audiovisual-congruency training compared with the remaining training conditions for younger, but not older, participants. Also, at the time of the N2, distributed source analysis revealed an enhancement of neural activity induced by audiovisual-congruency training in dorsolateral prefrontal cortex (Brodmann area 9) for the younger group. These findings suggest that cross-modal processes induced by audiovisual-congruency training under "cocktail-party" conditions at a short time scale resulted in an enhancement of correlates of auditory selective spatial attention.

Neurophysiological investigation of auditory intensity dependence in patients with Parkinson's disease

There is accumulating evidence for auditory dysfunctions in patients with Parkinson's disease (PD). Moreover, a possible relationship has been suggested between altered auditory intensity processing and the hypophonic speech characteristics in PD. Nonetheless, further insight into the neurophysiological correlates of auditory intensity processing in patients with PD is needed primarily. In the present study, high-density EEG recordings were used to investigate intensity dependence of auditory evoked potentials (IDAEPs) in 14 patients with PD and 14 age- and gender-matched healthy control participants (HCs). Patients with PD were evaluated in both the on- and off-medication states. HCs were also evaluated twice. Significantly increased IDAEP of the N1/P2 was demonstrated in patients with PD evaluated in the on-medication state compared to HCs. Distinctive results were found for the N1 and P2 component. Regarding the N1 component, no differences in latency or amplitude were shown between patients with PD and HCs regardless of the medication state. In contrast, increased P2 amplitude was demonstrated in patients with PD evaluated in the on-medication state compared to the off-medication state and HCs. In addition to a dopaminergic deficiency, deficits in serotonergic neurotransmission in PD were shown based on increased IDAEP. Due to specific alterations of the N1-P2 complex, the current results suggest deficiencies in early-attentive inhibitory processing of auditory input in PD. This interpretation is consistent with the involvement of the basal ganglia and the role of dopaminergic and serotonergic neurotransmission in auditory gating.

A test of model classes accounting for individual differences in the cocktail-party effect

Listeners differ widely in the ability to follow the speech of a single talker in a noisy crowd-what is called the cocktail-party effect. Differences may arise for any one or a combination of factors associated with auditory sensitivity, selective attention, working memory, and decision making required for effective listening. The present study attempts to narrow the possibilities by grouping explanations into model classes based on model predictions for the types of errors that distinguish better from poorer performing listeners in a vowel segregation and talker identification task. Two model classes are considered: those for which the errors are predictably tied to the voice variation of talkers (decision weight models) and those for which the errors occur largely independently of this variation (internal noise models). Regression analyses of trial-by-trial responses, for different tasks and task demands, show overwhelmingly that the latter type of error is responsible for the performance differences among listeners. The results are inconsistent with models that attribute the performance differences to differences in the reliance listeners place on relevant voice features in this decision. The results are consistent instead with models for which largely stimulus-independent, stochastic processes cause information loss at different stages of auditory processing.

Transcranial direct current stimulation of posterior temporal cortex modulates electrophysiological correlates of auditory selective spatial attention in posterior parietal cortex

Speech perception in "cocktail-party" situations, in which a sound source of interest has to be extracted out of multiple irrelevant sounds, poses a remarkable challenge to the human auditory system. Studies on structural and electrophysiological correlates of auditory selective spatial attention revealed critical roles of the posterior temporal cortex and the N2 event-related potential (ERP) component in the underlying processes. Here, we explored effects of transcranial direct current stimulation (tDCS) to posterior temporal cortex on neurophysiological correlates of auditory selective spatial attention, with a specific focus on the N2. In a single-blind, sham-controlled crossover design with baseline and follow-up measurements, monopolar anodal and cathodal tDCS was applied for 16 min to the right posterior superior temporal cortex. Two age groups of human subjects, a younger (n = 20; age 18-30 yrs) and an older group (n = 19; age 66-77 yrs), completed an auditory free-field multiple-speakers localization task while ERPs were recorded. The ERP data showed an offline effect of anodal, but not cathodal, tDCS immediately after DC offset for targets contralateral, but not ipsilateral, to the hemisphere of tDCS, without differences between groups. This effect mainly consisted in a substantial increase of the N2 amplitude by 0.9 μV (SE 0.4 μV; d = 0.40) compared with sham tDCS. At the same point in time, cortical source localization revealed a reduction of activity in ipsilateral (right) posterior parietal cortex. Also, localization error was improved after anodal, but not cathodal, tDCS. Given that both the N2 and the posterior parietal cortex are involved in processes of auditory selective spatial attention, these results suggest that anodal tDCS specifically enhanced inhibitory attentional brain processes underlying the focusing onto a target sound source, possibly by improved suppression of irrelevant distracters.

The Effect of Aging and Priming on Same/Different Judgments Between Text and Partially Masked Speech

OBJECTIVES

It is well known from previous research that when listeners are told what they are about to hear before a degraded or partially masked auditory signal is presented, the speech signal "pops out" of the background and becomes considerably more intelligible. The goal of this research was to explore whether this priming effect is as strong in older adults as in younger adults.

DESIGN

Fifty-six adults-28 older and 28 younger-listened to "nonsense" sentences spoken by a female talker in the presence of a 2-talker speech masker (also female) or a fluctuating speech-like noise masker at 5 signal-to-noise ratios. Just before, or just after, the auditory signal was presented, a typed caption was displayed on a computer screen. The caption sentence was either identical to the auditory sentence or differed by one key word. The subjects' task was to decide whether the caption and auditory messages were the same or different. Discrimination performance was reported in d'. The strength of the pop-out perception was inferred from the improvement in performance that was expected from the caption-before order of presentation. A subset of 12 subjects from each group made confidence judgments as they gave their responses, and also completed several cognitive tests.

RESULTS

Data showed a clear order effect for both subject groups and both maskers, with better same-different discrimination performance for the caption-before condition than the caption-after condition. However, for the two-talker masker, the younger adults obtained a larger and more consistent benefit from the caption-before order than the older adults across signal-to-noise ratios. Especially at the poorer signal-to-noise ratios, older subjects showed little evidence that they experienced the pop-out effect that is presumed to make the discrimination task easier. On average, older subjects also appeared to approach the task differently, being more reluctant than younger subjects to report that the captions and auditory sentences were the same. Correlation analyses indicated a significant negative association between age and priming benefit in the two-talker masker and nonsignificant associations between priming benefit in this masker and either high-frequency hearing loss or performance on the cognitive tasks.

CONCLUSIONS

Previous studies have shown that older adults are at least as good, if not better, at exploiting context in speech recognition, as compared with younger adults. The current results are not in disagreement with those findings but suggest that, under some conditions, the automatic priming process that may contribute to benefits from context is not as strong in older as in younger adults.

How repetition influences speech understanding by younger, middle-aged and older adults

OBJECTIVE

To examine benefit from immediate repetition of a masked speech message in younger, middle-aged and older adults.

DESIGN

Participants listened to sentences in conditions where only the target message was repeated, and when both the target message and its accompanying masker (noise or speech) were repeated. In a follow-up experiment, the effect of repetition was evaluated using a square-wave modulated noise masker to compare benefit when listeners were exposed to the same glimpses of the target message during first and second presentation versus when the glimpses differed.

STUDY SAMPLE

Younger, middle-aged and older adults (n = 16/group) for the main experiment; 15 younger adults for the follow-up experiment.

RESULTS

Repetition benefit was larger when the target but not the masker was repeated for all groups. This was especially true for older adults, suggesting that these individuals may be more negatively affected when a background message is repeated. Data obtained using noise maskers suggest that it is slightly more beneficial when listeners hear different (versus identical) portions of speech between initial presentation and repetition.

CONCLUSIONS

Although subtle age-related differences were found in some conditions, results confirm that repetition is an effective repair strategy for listeners spanning the adult age range.

Age-Related Changes in Objective and Subjective Speech Perception in Complex Listening Environments

PURPOSE

A frequent complaint by older adults is difficulty communicating in challenging acoustic environments. The purpose of this work was to review and summarize information about how speech perception in complex listening situations changes across the adult age range.

METHOD

This article provides a review of age-related changes in speech understanding in complex listening environments and summarizes results from several studies conducted in our laboratory.

RESULTS

Both degree of high frequency hearing loss and cognitive test performance limit individuals' ability to understand speech in difficult listening situations as they age. The performance of middle-aged adults is similar to that of younger adults in the presence of noise maskers, but they experience substantially more difficulty when the masker is 1 or 2 competing speech messages. For the most part, middle-aged participants in studies conducted in our laboratory reported as much self-perceived hearing problems as did older adult participants.

CONCLUSIONS

Research supports the multifactorial nature of listening in real-world environments. Current audiologic assessment practices are often insufficient to identify the true speech understanding struggles that individuals experience in these situations. This points to the importance of giving weight to patients' self-reported difficulties.

PRESENTATION VIDEO

http://cred.pubs.asha.org/article.aspx?articleid=2601619.

Switching of auditory attention in "cocktail-party" listening: ERP evidence of cueing effects in younger and older adults

Verbal communication in a "cocktail-party situation" is a major challenge for the auditory system. In particular, changes in target speaker usually result in declined speech perception. Here, we investigated whether speech cues indicating a subsequent change in target speaker reduce the costs of switching in younger and older adults. We employed event-related potential (ERP) measures and a speech perception task, in which sequences of short words were simultaneously presented by four speakers. Changes in target speaker were either unpredictable or semantically cued by a word within the target stream. Cued changes resulted in a less decreased performance than uncued changes in both age groups. The ERP analysis revealed shorter latencies in the change-related N400 and late positive complex (LPC) after cued changes, suggesting an acceleration in context updating and attention switching. Thus, both younger and older listeners used semantic cues to prepare changes in speaker setting.

Age equivalence in the benefit of repetition for speech understanding

Although repetition is the most commonly used conversational repair strategy, little is known about its relative effectiveness among listeners spanning the adult age range. The purpose of this study was to identify differences in how younger, middle-aged, and older adults were able to use immediate repetition to improve speech recognition in the presence of different kinds of maskers. Results suggest that all groups received approximately the same amount of benefit from repetition. Repetition benefit was largest when the masker was fluctuating noise and smallest when it was competing speech.

Effects of age on electrophysiological correlates of speech processing in a dynamic "cocktail-party" situation

Successful speech perception in multi-speaker environments depends on auditory scene analysis, comprising auditory object segregation and grouping, and on focusing attention toward the speaker of interest. Changes in speaker settings (e.g., in speaker position) require object re-selection and attention re-focusing. Here, we tested the processing of changes in a realistic multi-speaker scenario in younger and older adults, employing a speech-perception task, and event-related potential (ERP) measures. Sequences of short words (combinations of company names and values) were simultaneously presented via four loudspeakers at different locations, and the participants responded to the value of a target company. Voice and position of the speaker of the target information were kept constant for a variable number of trials and then changed. Relative to the pre-change level, changes caused higher error rates, and more so in older than younger adults. The ERP analysis revealed stronger fronto-central N2 and N400 components in younger adults, suggesting a more effective inhibition of concurrent speech stimuli and enhanced language processing. The difference ERPs (post-change minus pre-change) indicated a change-related N400 and late positive complex (LPC) over parietal areas in both groups. Only the older adults showed an additional frontal LPC, suggesting increased allocation of attentional resources after changes in speaker settings. In sum, changes in speaker settings are critical events for speech perception in multi-speaker environments. Especially older persons show deficits that could be based on less flexible inhibitory control and increased distraction.

The mismatch negativity as a measure of auditory stream segregation in a simulated "cocktail-party" scenario: effect of age

With age the ability to understand speech in multitalker environments usually deteriorates. The central auditory system has to perceptually segregate and group the acoustic input into sequences of distinct auditory objects. The present study used electrophysiological measures to study effects of age on auditory stream segregation in a multitalker scenario. Younger and older adults were presented with streams of short speech stimuli. When a single target stream was presented, the occurrence of a rare (deviant) syllable among a frequent (standard) syllable elicited the mismatch negativity (MMN), an electrophysiological correlate of automatic deviance detection. The presence of a second, concurrent stream consisting of the deviant syllable of the target stream reduced the MMN amplitude, especially when located nearby the target stream. The decrease in MMN amplitude indicates that the rare syllable of the target stream was less perceived as deviant, suggesting reduced stream segregation with decreasing stream distance. Moreover, the presence of a concurrent stream increased the MMN peak latency of the older group but not that of the younger group. The results provide neurophysiological evidence for the effects of concurrent speech on auditory processing in older adults, suggesting that older adults need more time for stream segregation in the presence of concurrent speech.