Cross-modal interactions at the audiovisual cocktail-party revealed by behavior, ERPs, and neural oscillations.

Theories of attention argue that objects are the units of attentional selection. In real-word environments such objects can contain visual and auditory features. To understand how mechanisms of selective attention operate in multisensory environments, in this pre-registered study, we created an audiovisual cocktail-party situation, in which two speakers (left and right of fixation) simultaneously articulated brief numerals. In three separate blocks, informative auditory speech was presented (a) alone or paired with (b) congruent or (c) uninformative visual speech. In all blocks, subjects localized a pre-defined numeral. While audiovisual-congruent and uninformative speech improved response times and speed of information uptake according to diffusion modeling, an ERP analysis revealed that this did not coincide with enhanced attentional engagement. Yet, consistent with object-based attentional selection, the deployment of auditory spatial attention (N2ac) was accompanied by visuo-spatial attentional orienting (N2pc) irrespective of the informational content of visual speech. Notably, an N2pc component was absent in the auditory-only condition, demonstrating that a sound-induced shift of visuo-spatial attention relies on the availability of audio-visual features evolving coherently in time. Additional exploratory analyses revealed cross-modal interactions in working memory and modulations of cognitive control.

Using visual speech at the cocktail-party: CNV evidence for early speech extraction in younger and older adults.

The comprehension of spoken language benefits from visual speech information. One reason for this is the temporal lead of mouth and lip movements over the onset of acoustic speech utterance. Here, we investigated EEG event-related potentials preceding acoustic speech, focusing on a fronto-central contingent negative variation (CNV) prior to the onset of acoustic speech. We explored influences of expectation and visual speech content as well as age-related differences. In a multi-talker two-alternative speech discrimination task, younger and older subjects responded to short words presented simultaneously to competing speech under free-field conditions. Subjects were always presented with audiovisual speech stimuli, while the modality containing the task-relevant information was modulated in a block-wise fashion. Thus, task-relevant speech information was either available as audio-visually congruent stimuli or only in the visual (visual-valid) or the auditory (auditory-valid) modality. Subjects were instructed to fixate a pre-specified position in the left or right hemispace. In each task block, task-relevant stimuli appeared either at the pre-specified position (standard trials, 80%) or at a rare deviant position (20%). Target words were recognized faster and more accurately when visual speech information was available. The CNV prior to the acoustic speech onset was more pronounced with visual-informative than with visually non-informative speech. Especially in the younger group, a less pronounced CNV occurred with purely visual speech in deviant trials, that is, when a task-irrelevant speech stimulus appeared instead of the expected target stimulus. The results indicate that processes preceding the onset of acoustic speech are modulated by expectations and visual speech content, while age differences are rather small.

The role of informational content of visual speech in an audiovisual cocktail party: Evidence from cortical oscillations in young and old participants.

Age-related differences in the processing of audiovisual speech in a multi-talker environment were investigated analysing event-related spectral perturbations (ERSPs), focusing on theta, alpha and beta oscillations that are assumed to reflect conflict processing, multisensory integration and attentional mechanisms, respectively. Eighteen older and 21 younger healthy adults completed a two-alternative forced-choice word discrimination task, responding to audiovisual speech stimuli. In a cocktail-party scenario with two competing talkers (located at -15° and 15° azimuth), target words (/yes/or/no/) appeared at a pre-defined (attended) position, distractor words at the other position. In two audiovisual conditions, acoustic speech was combined either with informative or uninformative visual speech. While a behavioural benefit for informative visual speech occurred for both age groups, differences between audiovisual conditions in the theta and beta band were only present for older adults. A stronger increase in theta perturbations for stimuli containing uninformative visual speech could be associated with early conflict processing, while a stronger suppression in beta perturbations for informative visual speech could be associated to audiovisual integration. Compared to the younger group, the older group showed generally stronger beta perturbations. No condition differences in the alpha band were found. Overall, the findings suggest age-related differences in audiovisual speech integration in a multi-talker environment. While the behavioural benefit of informative visual speech was unaffected by age, older adults had a stronger need for cognitive control when processing conflicting audiovisual speech input. Furthermore, mechanisms of audiovisual integration are differently activated depending on the informational content of the visual information.

Preparing for the unknown: How working memory provides a link between perception and anticipated action.

What mechanisms underlie the transfer of a working memory representation into a higher-level code for guiding future actions? Electrophysiological correlates of attentional selection and motor preparation processes within working memory were investigated in two retrospective cuing tasks. In the first experiment, participants stored the orientation and location of a grating. Subsequent feature cues (selective vs. neutral) indicated which feature would be the target for later report. The oscillatory response in the mu and beta frequency range with an estimated source in the sensorimotor cortex contralateral to the responding hand was used as correlate of motor preparation. Mu/beta suppression was stronger following the selective feature cues compared to the neutral cue, demonstrating that purely feature-based selection is sufficient to form a prospective motor plan. In the second experiment, another retrospective cue was included to study whether knowledge of the task at hand is necessary to initiate motor preparation. Following the feature cue, participants were cued to either compare the stored feature(s) to a probe stimulus (recognition task) or to adjust the memory probe to match the target feature (continuous report task). An analogous suppression of mu oscillations was observed following a selective feature cue, even ahead of task specification. Further, a subsequent selective task cue again elicited a mu/beta suppression, which was stronger after a continuous report task cue. This indicates that working memory is able to flexibly store different types of information in higher-level mental codes to provide optimal prerequisites for all required action possibilities.

Attentional modulations of alpha power are sensitive to the task-relevance of auditory spatial information.

The topographical distribution of oscillatory power in the alpha band is known to vary depending on the current focus of spatial attention. Here, we investigated to what extend univariate and multivariate measures of post-stimulus alpha power are sensitive to the required spatial specificity of a task. To this end, we varied the perceptual load and the spatial demand in an auditory search paradigm. A centrally presented sound at the beginning of each trial indicated the to-be-localized target sound. This spatially unspecific pre-cue was followed by a sound array, containing either two (low perceptual load) or four (high perceptual load) simultaneously presented lateralized sound stimuli. In separate task blocks, participants were instructed either to report whether the target was located on the left or the right side of the sound array (low spatial demand) or to indicate the exact target location (high spatial demand). Univariate alpha lateralization magnitude was neither affected by perceptual load nor by spatial demand. However, an analysis of onset latencies revealed that alpha lateralization emerged earlier in low (vs high) perceptual load trials as well as in low (vs high) spatial demand trials. Finally, we trained a classifier to decode the specific target location based on the multivariate alpha power scalp topography. A comparison of decoding accuracy in the low and high spatial demand conditions suggests that the amount of spatial information present in the scalp distribution of alpha-band power increases as the task demands a higher degree of spatial specificity. Altogether, the results offer new insights into how the dynamic adaption of alpha-band oscillations in response to changing task demands is associated with post-stimulus attentional processing.

Target enhancement or distractor suppression? Functionally distinct alpha oscillations form the basis of attention.

Recent advances in attention research have been propelled by the debate on target enhancement versus distractor suppression. A predominant neural correlate of attention is the modulation of alpha oscillatory power (~10 Hz), which signifies shifts of attention in time, space and between sensory modalities. However, the underspecified functional role of alpha oscillations limits the progress of tracking down the neurocognitive basis of attention. In this short opinion article, we review and critically examine a synthesis of three conceptual and methodological aspects that are indispensable for a mechanistic understanding of the role of alpha oscillations for attention. (a) Precise mapping of the anatomical source and the temporal response profile of neural signals reveals distinct alpha oscillatory processes that implement facilitatory versus suppressive components of attention. (b) A testable framework enables unanimous association of alpha modulation with either target enhancement or different forms of distractor suppression (active vs. automatic). (c) Linking anatomically specified alpha oscillations to behavior reveals the causal nature of alpha oscillations for attention. The three reviewed aspects substantially enrich study design, data analysis and interpretation of results to achieve the goal of understanding how anatomically specified and functionally relevant neural oscillations contribute to the implementation of facilitatory versus suppressive components of attention.

Do congruent lip movements facilitate speech processing in a dynamic audiovisual multi-talker scenario? An ERP study with older and younger adults.

In natural conversations, visible mouth and lip movements play an important role in speech comprehension. There is evidence that visual speech information improves speech comprehension, especially for older adults and under difficult listening conditions. However, the neurocognitive basis is still poorly understood. The present EEG experiment investigated the benefits of audiovisual speech in a dynamic cocktail-party scenario with 22 (aged 20-34 years) younger and 20 (aged 55-74 years) older participants. We presented three simultaneously talking faces with a varying amount of visual speech input (still faces, visually unspecific and audiovisually congruent). In a two-alternative forced-choice task, participants had to discriminate target words ("yes" or "no") among two distractors (one-digit number words). In half of the experimental blocks, the target was always presented from a central position, in the other half, occasional switches to a lateral position could occur. We investigated behavioral and electrophysiological modulations due to age, location switches and the content of visual information, analyzing response times and accuracy as well as the P1, N1, P2, N2 event-related potentials (ERPs) and the contingent negative variation (CNV) in the EEG. We found that audiovisually congruent speech information improved performance and modulated ERP amplitudes in both age groups, suggesting enhanced preparation and integration of the subsequent auditory input. In the older group, larger amplitude measures were found in early phases of processing (P1-N1). Here, amplitude measures were reduced in response to audiovisually congruent stimuli. In later processing phases (P2-N2) we found decreased amplitude measures in the older group, while an amplitude reduction for audiovisually congruent compared to visually unspecific stimuli was still observable. However, these benefits were only observed as long as no location switches occurred, leading to enhanced amplitude measures in later processing phases (P2-N2). To conclude, meaningful visual information in a multi-talker setting, when presented from the expected location, is shown to be beneficial for both younger and older adults.

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.

A dual mechanism underlying retroactive shifts of auditory spatial attention: dissociating target- and distractor-related modulations of alpha lateralization.

Attention can be allocated to mental representations to select information from working memory. To date, it remains ambiguous whether such retroactive shifts of attention involve the inhibition of irrelevant information or the prioritization of relevant information. Investigating asymmetries in posterior alpha-band oscillations during an auditory retroactive cueing task, we aimed at differentiating those mechanisms. Participants were cued to attend two out of three sounds in an upcoming sound array. Importantly, the resulting working memory representation contained one laterally and one centrally presented item. A centrally presented retro-cue then indicated the lateral, the central, or both items as further relevant for the task (comparing the cued item(s) to a memory probe). Time-frequency analysis revealed opposing patterns of alpha lateralization depending on target eccentricity: A contralateral decrease in alpha power in target lateral trials indicated the involvement of target prioritization. A contralateral increase in alpha power when the central item remained relevant (distractor lateral trials) suggested the de-prioritization of irrelevant information. No lateralization was observed when both items remained relevant, supporting the notion that auditory alpha lateralization is restricted to situations in which spatial information is task-relevant. Altogether, the data demonstrate that retroactive attentional deployment involves excitatory and inhibitory control mechanisms.

Unraveling the Relation between EEG Correlates of Attentional Orienting and Sound Localization Performance: A Diffusion Model Approach.

Understanding the contribution of cognitive processes and their underlying neurophysiological signals to behavioral phenomena has been a key objective in recent neuroscience research. Using a diffusion model framework, we investigated to what extent well-established correlates of spatial attention in the electroencephalogram contribute to behavioral performance in an auditory free-field sound localization task. Younger and older participants were instructed to indicate the horizontal position of a predefined target among three simultaneously presented distractors. The central question of interest was whether posterior alpha lateralization and amplitudes of the anterior contralateral N2 subcomponent (N2ac) predict sound localization performance (accuracy, mean RT) and/or diffusion model parameters (drift rate, boundary separation, non-decision time). Two age groups were compared to explore whether, in older adults (who struggle with multispeaker environments), the brain-behavior relationship would differ from younger adults. Regression analyses revealed that N2ac amplitudes predicted drift rate and accuracy, whereas alpha lateralization was not related to behavioral or diffusion modeling parameters. This was true irrespective of age. The results indicate that a more efficient attentional filtering and selection of information within an auditory scene, reflected by increased N2ac amplitudes, was associated with a higher speed of information uptake (drift rate) and better localization performance (accuracy), while the underlying response criteria (threshold separation), mean RTs, and non-decisional processes remained unaffected. The lack of a behavioral correlate of poststimulus alpha power lateralization constrasts with the well-established notion that prestimulus alpha power reflects a functionally relevant attentional mechanism. This highlights the importance of distinguishing anticipatory from poststimulus alpha power modulations.

Retroactive Attentional Shifts Predict Performance in a Working Memory Task: Evidence by Lateralized EEG Patterns.

Shifts of attention within working memory based on retroactive (retro-) cues were shown to facilitate performance in working memory tasks. Although posterior asymmetries in the EEG, such as the contralateral delay activity (CDA), have been used to study the active storage of lateralized working memory representations, results on the relation of such asymmetric effects to retro-cue benefits remain inconclusive. We recorded EEG in a retro-cue working memory task with lateralized items and a continuous performance response. Following either a selective or neutral retro-cue, participants adjusted the orientation of a central memory probe to the cued item. Selective retro-cues elicited an early posterior contralateral negativity (PCN), anterior directing attention negativity (ADAN) and a later modulation of CDA indicating that active storage was concentrated on the cued information. By dividing all trials into three within-condition performance quantiles, we could further show that high working memory accuracy was associated with a sustained increase of the CDA effect following the retro-cue. These results suggest that focusing resources on the active storage of relevant representations is an important factor regarding retro-cue benefits in working memory tasks.

The contribution of selective spatial attention to sound detection and sound localization: Evidence from event-related potentials and lateralized alpha oscillations.

Auditory selective attention can be directed toward spatial and non-spatial stimulus features. Here, we studied electrophysiological correlates of spatial attention under spatially-specific and purely feature-based demands. Using an auditory search paradigm, in which participants performed a target localization (left versus right) and a target detection task (present versus absent), we investigated whether attentional selection of a relevant sound from a two- or four-sound array necessarily involves the processing of spatial sound information. While the early N2 anterior contralateral component occurred irrespective of task, the subsequent lateralization of alpha power oscillations (8-12 Hz) over parieto-occipital scalp was modulated by the task-relevance of spatial information. Thus, the two correlates appear to reflect differential aspects of attentional orienting: We propose that the N2ac reflects an initial, modality-specific focusing of attention onto a lateralized target, while the subsequent alpha lateralization appears associated with the spatiotopic access to presumably supramodal representations of the sound array.

Searching for auditory targets in external space and in working memory: Electrophysiological mechanisms underlying perceptual and retroactive spatial attention.

Attention can be shifted within internal representations maintained in working memory. These retroactive processes are particularly inherent to the processing of auditory information that is especially transient over time and thus, requires us to continuously maintain, attend to, and integrate information in working memory. Using EEG recordings, the present study investigated the neurophysiological mechanisms underlying selective spatial attention in a retroactive as opposed to a perceptual auditory search task. Two kinds of sound stimuli were employed: a horizontal sound array consisting of two natural sounds presented simultaneously in the left and right hemispace and a central single target sound. The target sound was provided either after (retroactive search) or before the presentation of the sound array (perceptual search). In both search conditions, participants completed a sound localization and a sound detection task, indicating the position (left or right) or the presence versus absence (yes or no) of a particular target sound. Analyses revealed a lateralization of alpha power oscillations (8-12 Hz) over parieto-occipital scalp in both perceptual and retroactive sound localization tasks, but not in respective sound detection tasks, suggesting auditory alpha lateralization to be restricted to spatially-specific task demands. The observed asymmetric modulations of alpha power in sound localization are consistent with analogous findings from the visual domain, supporting the supramodal role of alpha oscillations in the deployment of spatial attention. Hence, we conclude that auditory alpha lateralization is a higher-order attention mechanism that operates in perceptual and mnemonic space reflecting the access to a spatially-specific, supramodal response template.

Psychological flexibility mediates the effect of an online-based acceptance and commitment therapy for chronic pain: an investigation of change processes.

One way to improve treatment effects of chronic pain is to identify and improve control over mechanisms of therapeutic change. One treatment approach that includes a specific proposed mechanism is acceptance and commitment therapy (ACT) with its focus on increasing psychological flexibility (PF). The aim of the present study was to examine the role of PF as a mechanism of change in ACT. This is based on mediation analyses of data from a previously reported randomized controlled trial, evaluating the effectiveness of an ACT-based online intervention for chronic pain (ACTonPain). We performed secondary analyses on pretreatment, posttreatment, and follow-up data from 302 adults, receiving a guided (n = 100) or unguided (n = 101) version of ACTonPain, or allocated to the waitlist control group (n = 101). Structural equation modelling and a bias-corrected bootstrap approach were applied to examine the indirect effects of the treatment through pretreatment and posttreatment changes in the latent construct reflecting PF. The latent construct consisted of data from the Chronic Pain Acceptance Questionnaire and the Acceptance and Action Questionnaire. The outcomes were pretreatment to follow-up changes in pain interference, anxiety, depression, pain, and mental and physical health. Structural equation modelling analyses revealed that changes in PF significantly mediated pretreatment to follow-up changes in all outcomes in the intervention groups compared with waitlist (standardized estimates ranged from I0.16I to I0.69I). Global model fit yielded modest but acceptable results. Findings are consistent with the theoretical framework behind ACT and contribute to growing evidence, supporting a focus on PF to optimize treatment effects.