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

The relationship between music training and cognitive flexibility: an ERP study

Background

Music training involves several cognitive functions in the brain, particularly executive function. Numerous studies have proven a link between the two. Cognitive flexibility is an important component of executive function, however, there has been little study investigating the association between music training and cognitive flexibility.

Method

Music training (N = 22) and the control groups (N = 26) were included in the present study. A tone-related oddball task was used to investigate the tone-related inhibition and the switch task was to investigate cognitive flexibility. During the switch task, EEG data were collected.

Results

The behavioral results of the oddball task showed that the individuals in the music training group had a shorter reaction time and higher accuracy in both the between-tone and within-tone categories compared to the controls. The behavioral results of the switch task showed similar results, with the music training group exhibiting better reaction time and accuracy performance than the controls. ERP results showed that the music training group had smaller P3 amplitudes and greater N2 and N450 amplitudes than the control group.

Discussion

The findings further supported the link between music training and enhanced cognitive function.

Effects of Spatial Speech Presentation on Listener Response Strategy for Talker-Identification

This study investigates effects of spatial auditory cues on human listeners' response strategy for identifying two alternately active talkers (“turn-taking” listening scenario). Previous research has demonstrated subjective benefits of audio spatialization with regard to speech intelligibility and talker-identification effort. So far, the deliberate activation of specific perceptual and cognitive processes by listeners to optimize their task performance remained largely unexamined. Spoken sentences selected as stimuli were either clean or degraded due to background noise or bandpass filtering. Stimuli were presented via three horizontally positioned loudspeakers: In a non-spatial mode, both talkers were presented through a central loudspeaker; in a spatial mode, each talker was presented through the central or a talker-specific lateral loudspeaker. Participants identified talkers via speeded keypresses and afterwards provided subjective ratings (speech quality, speech intelligibility, voice similarity, talker-identification effort). In the spatial mode, presentations at lateral loudspeaker locations entailed quicker behavioral responses, which were significantly slower in comparison to a talker-localization task. Under clean speech, response times globally increased in the spatial vs. non-spatial mode (across all locations); these “response time switch costs,” presumably being caused by repeated switching of spatial auditory attention between different locations, diminished under degraded speech. No significant effects of spatialization on subjective ratings were found. The results suggested that when listeners could utilize task-relevant auditory cues about talker location, they continued to rely on voice recognition instead of localization of talker sound sources as primary response strategy. Besides, the presence of speech degradations may have led to increased cognitive control, which in turn compensated for incurring response time switch costs.

Revealing Perceptional and Cognitive Mechanisms in Static and Dynamic Cocktail Party Listening by Means of Error Analyses

In cocktail party situations multiple talkers speak simultaneously, which causes listening to be perceptually and cognitively challenging. Such situations can either be static (fixed target talker) or dynamic, meaning the target talker switches occasionally and in a potentially unpredictable way. To shed light on the perceptional and cognitive mechanisms in static and dynamic cocktail party situations, we conducted an analysis of error types that occur during a multi-talker speech recognition test. The error analysis distinguished between misunderstood or omitted words (random errors) and target-masker confusions. To investigate the effects of aging and hearing impairment, we compared data from three listener groups, comprised of young as well as older adults with and without hearing loss. In the static condition, error rates were generally very low, except for the older hearing-impaired listeners. Consistent with the assumption of decreased audibility, they showed a notable amount of random errors. In the dynamic condition, errors increased compared to the static condition, especially immediately following a target talker switch. Those increases were similar for random and confusion errors. The older hearing-impaired listeners showed greater difficulties than the younger adults in trials not preceded by a switch. These results suggest that the load associated with dynamic cocktail party listening affects the ability to focus attention on the talker of interest and the retrieval of words from short-term memory, as indicated by the increased amount of confusion and random errors. This was most pronounced in the older hearing-impaired listeners proposing an interplay of perceptual and cognitive mechanisms.

Costs of dynamic cocktail party listening: Investigating the effects of cognitive abilities and hearing impairment

Situations with multiple competing talkers are especially challenging for listeners with hearing impairment. These "cocktail party" situations can either be static (fixed target talker) or dynamic (changing target talker). Relative to static situations, dynamic listening is typically associated with increased cognitive load and decreased speech recognition ("costs"). This study addressed the role of hearing impairment and cognition in two groups of older listeners with and without hearing loss. In most of the dynamic situations, the costs did not differ between the listener groups. There was no clear evidence that overall costs show an association with the individuals' cognitive abilities.

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.

Age-related dissociation of N400 effect and lexical priming

The use of contextual information is an important capability to facilitate language comprehension. This can be shown by studying behavioral and neurophysiological measures of accelerated word recognition when semantically or phonemically related information is provided in advance, resulting in accompanying attenuation of the respective event-related potential, i.e. the N400 effect. Against the background of age-dependent changes in a broad variety of lexical capacities, we aimed to study whether word priming is accomplished differently in elderly compared to young persons. 19 young (29.9 ± 5.6 years) and 15 older (69.0 ± 7.2 years) healthy adults participated in a primed lexical decision task that required the classification of target stimuli (words or pseudo-words) following related or unrelated prime words. We assessed reaction time, task accuracy and N400 responses. Acceleration of word recognition by semantic and phonemic priming was significant in both groups, but resulted in overall larger priming effects in the older participants. Compared with young adults, the older participants were slower and less accurate in responding to unrelated word-pairs. The expected N400 effect was smaller in older than young adults, particularly during phonemic word and pseudo-word priming, with a rather similar N400 amplitude reduction by semantic relatedness. The observed pattern of results is consistent with preserved or even enhanced lexical context sensitivity in older compared to young adults. This, however, appears to involve compensatory cognitive strategies with higher lexical processing costs during phonological processing in particular, suggested by a reduced N400 effect in the elderly.

Conversation in small groups: Speaking and listening strategies depend on the complexities of the environment and group

Many conversations in our day-to-day lives are held in noisy environments – impeding comprehension, and in groups – taxing auditory attention-switching processes. These situations are particularly challenging for older adults in cognitive and sensory decline. In noisy environments, a variety of extra-linguistic strategies are available to speakers and listeners to facilitate communication, but while models of language account for the impact of context on word choice, there has been little consideration of the impact of context on extra-linguistic behaviour. To address this issue, we investigate how the complexity of the acoustic environment and interaction situation impacts extra-linguistic conversation behaviour of older adults during face-to-face conversations. Specifically, we test whether the use of intelligibility-optimising strategies increases with complexity of the background noise (from quiet to loud, and in speech-shaped vs. babble noise), and with complexity of the conversing group (dyad vs. triad). While some communication strategies are enhanced in more complex background noise, with listeners orienting to talkers more optimally and moving closer to their partner in babble than speech-shaped noise, this is not the case with all strategies, as we find greater vocal level increases in the less complex speech-shaped noise condition. Other behaviours are enhanced in the more complex interaction situation, with listeners using more optimal head orientations, and taking longer turns when gaining the floor in triads compared to dyads. This study elucidates how different features of the conversation context impact individuals’ communication strategies, which is necessary to both develop a comprehensive cognitive model of multimodal conversation behaviour, and effectively support individuals that struggle conversing.

EEG correlates of spatial shifts of attention in a dynamic multi-talker speech perception scenario in younger and older adults

Speech perception under "cocktail-party" conditions critically depends on the focusing of attention toward the talker of interest. In dynamic auditory scenes, changes in talker settings require rapid shifts of attention, which is especially relevant when the position of a target talker switches from one location to another. Here, we explored electrophysiological correlates of shifts in spatial auditory attention, using a free-field speech perception task, in which sequences of short words (a company name, followed by a numeric value, e.g., "Bosch-6") were presented in the participants' left and right horizontal plane. Younger and older participants responded to the value of a pre-defined target company, while ignoring three simultaneously presented pairs of concurrent company names and values from different locations. All four stimulus pairs were spoken by different talkers, alternating from trial-to-trial. The location of the target company was within either the left or right hemisphere for a variable number of consecutive trials (between 3 and 42 trials) and then changed, switching from the left to the right hemispace or vice versa. Thus, when a switch occurred, the participants had to search for the new position of the target company among the concurrent streams of auditory information and re-focus their attention on the relevant location. As correlates of lateralized spatial auditory attention, the anterior contralateral N2 subcomponent (N2ac) and the posterior alpha power lateralization were analyzed in trials immediately before and after switches of the target location. Both measures were increased after switches, while only the increase in N2ac was related to better speech perception performance (i.e., a reduced post-switch decline in accuracy). While both age groups showed a similar pattern of switch-related attentional modulations, N2ac and alpha lateralization to the task-relevant stimulus (the target company's value) was overall greater in the younger, than older, group. The results suggest that N2ac and alpha lateralization reflect different attentional processes in multi-talker speech perception, the first being primarily associated with auditory search and the focusing of attention, and the second with the in-depth attentional processing of task-relevant information. Especially the second process appears to be prone to age-related cognitive decline.

Masking effects on subjective annoyance to aircraft flyover noise: An fMRI study

Sound masking, a new noise control technology, has been applied to improve subjective perception of noise in recent years. However, the neural mechanisms underlying this technology are still unclear. In this study, 18 healthy subjects were recurited to take subjective annoyance assessments and fMRI scanning with the aircraft noise and the masked aircraft noise. The results showed that the noise annoyance was associated with deficient functional connectivity between anterior cingulate cortex (ACC) and prefrontal cortex and exceeded brain activation in ACC, which might be explained as compensation. The sound masking led to significantly strong activation in the left medial frontal cortex and right medial orbital frontal cortex, which were associated with happy emotion induced by sound masking. This study offered new insights on the underlying neural mechanisms of sound masking effects.

Probing the relationship between late endogenous ERP components with fluid intelligence in healthy older adults

The world population is rapidly aging, bringing together the necessity to better understand the advancing age. This characterization may be used to aid early diagnosis and to guide individually-tailored interventions. While some event-related potential (ERP) components, such as the P300 and late positive complex (LPC), have been associated with fluid intelligence (Gf) in young population; little is known whether these associations hold for older people. Therefore, the main goal of this study was to assess whether these ERP components are associated with Gf in the elderly. Fifty-seven older adults performed a continuous performance task (CPT) and a visual oddball paradigm while EEG was recorded. Participants were divided into two groups, according to their performance in the Raven’s Advanced Progressive Matrices test: high-performance (HP) and low-performance (LP). Results showed that the HP group, compared to the LP group, had higher LPC amplitudes in the CPT and shorter P300 latencies in the oddball task, highlighting the role of ERP components as a potential electrophysiological proxy of Gf abilities in the elderly.

The Effects of Switching Non-Spatial Attention During Conversational Turn Taking

This study examined the effect of a change in target voice on word recall during a multi-talker conversation. Two experiments were conducted using matrix sentences to assess the cost of a single endogenous switch in non-spatial attention. Performance in a yes-no recognition task was significantly worse when a target voice changed compared to when it remained the same after a turn-taking gap. We observed a decrease in target hit rate and sensitivity, and an increase in masker confusion errors following a change in voice. These results highlight the cognitive demands of not only engaging attention on a new talker, but also of disengaging attention from a previous target voice. This shows that exposure to a voice can have a biasing effect on attention that persists well after a turn-taking gap. A second experiment showed that there was no change in switching performance using different talker combinations. This demonstrates that switching costs were consistent and did not depend on the degree of acoustic differences in target voice characteristics.

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.

Evaluating the Performance of a Visually Guided Hearing Aid Using a Dynamic Auditory-Visual Word Congruence Task

OBJECTIVES

The "visually guided hearing aid" (VGHA), consisting of a beamforming microphone array steered by eye gaze, is an experimental device being tested for effectiveness in laboratory settings. Previous studies have found that beamforming without visual steering can provide significant benefits (relative to natural binaural listening) for speech identification in spatialized speech or noise maskers when sound sources are fixed in location. The aim of the present study was to evaluate the performance of the VGHA in listening conditions in which target speech could switch locations unpredictably, requiring visual steering of the beamforming. To address this aim, the present study tested an experimental simulation of the VGHA in a newly designed dynamic auditory-visual word congruence task.

DESIGN

Ten young normal-hearing (NH) and 11 young hearing-impaired (HI) adults participated. On each trial, three simultaneous spoken words were presented from three source positions (-30, 0, and 30 azimuth). An auditory-visual word congruence task was used in which participants indicated whether there was a match between the word printed on a screen at a location corresponding to the target source and the spoken target word presented acoustically from that location. Performance was compared for a natural binaural condition (stimuli presented using impulse responses measured on KEMAR), a simulated VGHA condition (BEAM), and a hybrid condition that combined lowpass-filtered KEMAR and highpass-filtered BEAM information (BEAMAR). In some blocks, the target remained fixed at one location across trials, and in other blocks, the target could transition in location between one trial and the next with a fixed but low probability.

RESULTS

Large individual variability in performance was observed. There were significant benefits for the hybrid BEAMAR condition relative to the KEMAR condition on average for both NH and HI groups when the targets were fixed. Although not apparent in the averaged data, some individuals showed BEAM benefits relative to KEMAR. Under dynamic conditions, BEAM and BEAMAR performance dropped significantly immediately following a target location transition. However, performance recovered by the second word in the sequence and was sustained until the next transition.

CONCLUSIONS

When performance was assessed using an auditory-visual word congruence task, the benefits of beamforming reported previously were generally preserved under dynamic conditions in which the target source could move unpredictably from one location to another (i.e., performance recovered rapidly following source transitions) while the observer steered the beamforming via eye gaze, for both young NH and young HI groups.

Intentional switching in auditory selective attention: Exploring age-related effects in a spatial setup requiring speech perception

Using a binaural-listening paradigm, age-related differences in the ability to intentionally switch auditory selective attention between two speakers, defined by their spatial location, were examined. Therefore 40 normal-hearing participants (20 young, Ø 24.8years; 20 older Ø 67.8years) were tested. The spatial reproduction of stimuli was provided by headphones using head-related-transfer-functions of an artificial head. Spoken number words of two speakers were presented simultaneously to participants from two out of eight locations on the horizontal plane. Guided by a visual cue indicating the spatial location of the target speaker, the participants were asked to categorize the target's number word into smaller vs. greater than five while ignoring the distractor's speech. Results showed significantly higher reaction times and error rates for older participants. The relative influence of the spatial switch of the target-speaker (switch or repetition of speaker's direction in space) was identical across age groups. Congruency effects (stimuli spoken by target and distractor may evoke the same answer or different answers) were increased for older participants and depend on the target's position. Results suggest that the ability to intentionally switch auditory attention to a new cued location was unimpaired whereas it was generally harder for older participants to suppress processing the distractor's speech.

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.

Effect of informational content of noise on speech representation in the aging midbrain and cortex

The ability to understand speech is significantly degraded by aging, particularly in noisy environments. One way that older adults cope with this hearing difficulty is through the use of contextual cues. Several behavioral studies have shown that older adults are better at following a conversation when the target speech signal has high contextual content or when the background distractor is not meaningful. Specifically, older adults gain significant benefit in focusing on and understanding speech if the background is spoken by a talker in a language that is not comprehensible to them (i.e., a foreign language). To understand better the neural mechanisms underlying this benefit in older adults, we investigated aging effects on midbrain and cortical encoding of speech when in the presence of a single competing talker speaking in a language that is meaningful or meaningless to the listener (i.e., English vs. Dutch). Our results suggest that neural processing is strongly affected by the informational content of noise. Specifically, older listeners' cortical responses to the attended speech signal are less deteriorated when the competing speech signal is an incomprehensible language rather than when it is their native language. Conversely, temporal processing in the midbrain is affected by different backgrounds only during rapid changes in speech and only in younger listeners. Additionally, we found that cognitive decline is associated with an increase in cortical envelope tracking, suggesting an age-related over (or inefficient) use of cognitive resources that may explain their difficulty in processing speech targets while trying to ignore interfering noise.

Behavioral and neurophysiological evidence for increased cognitive flexibility in late childhood

Executive functions, like the capacity to control and organize thoughts and behavior, develop from childhood to young adulthood. Although task switching and working memory processes are known to undergo strong developmental changes from childhood to adulthood, it is currently unknown how task switching processes are modulated between childhood and adulthood given that working memory processes are central to task switching. The aim of the current study is therefore to examine this question using a combined cue- and memory-based task switching paradigm in children (N = 25) and young adults (N = 25) in combination with neurophysiological (EEG) methods. We obtained an unexpected paradoxical effect suggesting that memory-based task switching is better in late childhood than in young adulthood. No group differences were observed in cue-based task switching. The neurophysiological data suggest that this effect is not due to altered attentional selection (P1, N1) or processes related to the updating, organization, and implementation of the new task-set (P3). Instead, alterations were found in the resolution of task-set conflict and the selection of an appropriate response (N2) when a task has to be switched. Our observation contrasts findings showing that cognitive control mechanisms reach their optimal functioning in early adulthood.