Selective attention to human voice enhances brain activity bilaterally in the superior temporal sulcus

Attention to audiovisual speech shapes neural processing through feedback-feedforward loops between different nodes of the speech network

Selective attention-related top-down modulation plays a significant role in separating relevant speech from irrelevant background speech when vocal attributes separating concurrent speakers are small and continuously evolving. Electrophysiological studies have shown that such top-down modulation enhances neural tracking of attended speech. Yet, the specific cortical regions involved remain unclear due to the limited spatial resolution of most electrophysiological techniques. To overcome such limitations, we collected both electroencephalography (EEG) (high temporal resolution) and functional magnetic resonance imaging (fMRI) (high spatial resolution), while human participants selectively attended to speakers in audiovisual scenes containing overlapping cocktail party speech. To utilise the advantages of the respective techniques, we analysed neural tracking of speech using the EEG data and performed representational dissimilarity-based EEG-fMRI fusion. We observed that attention enhanced neural tracking and modulated EEG correlates throughout the latencies studied. Further, attention-related enhancement of neural tracking fluctuated in predictable temporal profiles. We discuss how such temporal dynamics could arise from a combination of interactions between attention and prediction as well as plastic properties of the auditory cortex. EEG-fMRI fusion revealed attention-related iterative feedforward-feedback loops between hierarchically organised nodes of the ventral auditory object related processing stream. Our findings support models where attention facilitates dynamic neural changes in the auditory cortex, ultimately aiding discrimination of relevant sounds from irrelevant ones while conserving neural resources.

The words that little by little revealed everything: Neural response to lexical-semantic content during narrative comprehension

The ease with which narratives are understood belies the complexity of the information being conveyed and the cognitive processes that support comprehension. The meanings of the words must be rapidly accessed and integrated with the reader's mental representation of the overarching, unfolding scenario. A broad, bilateral brain network is engaged by this process, but it is not clear how words that vary on specific semantic dimensions, such as ambiguity, emotion, or socialness, engage the semantic, semantic control, or social cognition systems. In the present study, data from 48 participants who listened to The Little Prince audiobook during MRI scanning were selected from the Le Petit Prince dataset. The lexical and semantic content within the narrative was quantified from the transcript words with factor scores capturing Word Length, Semantic Flexibility, Emotional Strength, and Social Impact. These scores, along with word quantity variables, were used to investigate where these predictors co-vary with activation across the brain. In contrast to studies of isolated word processing, large networks were found to co-vary with the lexical and semantic content within the narrative. An increase in semantic content engaged the ventral portion of ventrolateral ATL, consistent with its role as a semantic hub. Decreased semantic content engaged temporal pole and inferior parietal lobule, which may reflect semantic integration. The semantic control network was engaged by words with low Semantic Flexibility, perhaps due to the demand required to process infrequent, less semantically diverse language. Activation in ATL co-varied with an increase in Social Impact, which is consistent with the claim that social knowledge is housed within the neural architecture of the semantic system. These results suggest that current models of language processing may present an impoverished estimate of the neural systems that coordinate to support narrative comprehension, and, by extension, real-world language processing.

Functional connectivity and gray matter deficits within the auditory attention circuit in first-episode psychosis

Background

Selective attention deficits in first episode of psychosis (FEP) can be indexed by impaired attentional modulation of auditory M100. It is unknown if the pathophysiology underlying this deficit is restricted to auditory cortex or involves a distributed attention network. We examined the auditory attention network in FEP.

Methods

MEG was recorded from 27 FEP and 31 matched healthy controls (HC) while alternately ignoring or attending tones. A whole-brain analysis of MEG source activity during auditory M100 identified non-auditory areas with increased activity. Time-frequency activity and phase-amplitude coupling were examined in auditory cortex to identify the attentional executive carrier frequency. Attention networks were defined by phase-locking at the carrier frequency. Spectral and gray matter deficits in the identified circuits were examined in FEP.

Results

Attention-related activity was identified in prefrontal and parietal regions, markedly in precuneus. Theta power and phase coupling to gamma amplitude increased with attention in left primary auditory cortex. Two unilateral attention networks were identified with precuneus seeds in HC. Network synchrony was impaired in FEP. Gray matter thickness was reduced within the left hemisphere network in FEP but did not correlate with synchrony.

Conclusion

Several extra-auditory attention areas with attention-related activity were identified. Theta was the carrier frequency for attentional modulation in auditory cortex. Left and right hemisphere attention networks were identified, with bilateral functional deficits and left hemisphere structural deficits, though FEP showed intact auditory cortex theta phase-gamma amplitude coupling. These novel findings indicate attention-related circuitopathy early in psychosis potentially amenable to future non-invasive interventions.

Brain activity during shadowing of audiovisual cocktail party speech, contributions of auditory-motor integration and selective attention

Selective listening to cocktail-party speech involves a network of auditory and inferior frontal cortical regions. However, cognitive and motor cortical regions are differentially activated depending on whether the task emphasizes semantic or phonological aspects of speech. Here we tested whether processing of cocktail-party speech differs when participants perform a shadowing (immediate speech repetition) task compared to an attentive listening task in the presence of irrelevant speech. Participants viewed audiovisual dialogues with concurrent distracting speech during functional imaging. Participants either attentively listened to the dialogue, overtly repeated (i.e., shadowed) attended speech, or performed visual or speech motor control tasks where they did not attend to speech and responses were not related to the speech input. Dialogues were presented with good or poor auditory and visual quality. As a novel result, we show that attentive processing of speech activated the same network of sensory and frontal regions during listening and shadowing. However, in the superior temporal gyrus (STG), peak activations during shadowing were posterior to those during listening, suggesting that an anterior-posterior distinction is present for motor vs. perceptual processing of speech already at the level of the auditory cortex. We also found that activations along the dorsal auditory processing stream were specifically associated with the shadowing task. These activations are likely to be due to complex interactions between perceptual, attention dependent speech processing and motor speech generation that matches the heard speech. Our results suggest that interactions between perceptual and motor processing of speech relies on a distributed network of temporal and motor regions rather than any specific anatomical landmark as suggested by some previous studies.

Brain Responses to Peer Feedback in Social Media Are Modulated by Valence in Late Adolescence

Previous studies have examined the neural correlates of receiving negative feedback from peers during virtual social interaction in young people. However, there is a lack of studies applying platforms adolescents use in daily life. In the present study, 92 late-adolescent participants performed a task that involved receiving positive and negative feedback to their opinions from peers in a Facebook-like platform, while brain activity was measured using functional magnetic resonance imaging (fMRI). Peer feedback was shown to activate clusters in the ventrolateral prefrontal cortex (VLPFC), medial prefrontal cortex (MPFC), superior temporal gyrus and sulcus (STG/STS), and occipital cortex (OC). Negative feedback was related to greater activity in the VLPFC, MPFC, and anterior insula than positive feedback, replicating previous findings on peer feedback and social rejection. Real-life habits of social media use did not correlate with brain responses to negative feedback.

Task-dependent cortical activations during selective attention to audiovisual speech

Selective listening to speech depends on widespread networks of the brain, but how the involvement of different neural systems in speech processing is affected by factors such as the task performed by a listener and speech intelligibility remains poorly understood. We used functional magnetic resonance imaging to systematically examine the effects that performing different tasks has on neural activations during selective attention to continuous audiovisual speech in the presence of task-irrelevant speech. Participants viewed audiovisual dialogues and attended either to the semantic or the phonological content of speech, or ignored speech altogether and performed a visual control task. The tasks were factorially combined with good and poor auditory and visual speech qualities. Selective attention to speech engaged superior temporal regions and the left inferior frontal gyrus regardless of the task. Frontoparietal regions implicated in selective auditory attention to simple sounds (e.g., tones, syllables) were not engaged by the semantic task, suggesting that this network may not be not as crucial when attending to continuous speech. The medial orbitofrontal cortex, implicated in social cognition, was most activated by the semantic task. Activity levels during the phonological task in the left prefrontal, premotor, and secondary somatosensory regions had a distinct temporal profile as well as the highest overall activity, possibly relating to the role of the dorsal speech processing stream in sub-lexical processing. Our results demonstrate that the task type influences neural activations during selective attention to speech, and emphasize the importance of ecologically valid experimental designs.

Attentional Modulation of Hierarchical Speech Representations in a Multitalker Environment

Humans are remarkably adept in listening to a desired speaker in a crowded environment, while filtering out nontarget speakers in the background. Attention is key to solving this difficult cocktail-party task, yet a detailed characterization of attentional effects on speech representations is lacking. It remains unclear across what levels of speech features and how much attentional modulation occurs in each brain area during the cocktail-party task. To address these questions, we recorded whole-brain blood-oxygen-level-dependent (BOLD) responses while subjects either passively listened to single-speaker stories, or selectively attended to a male or a female speaker in temporally overlaid stories in separate experiments. Spectral, articulatory, and semantic models of the natural stories were constructed. Intrinsic selectivity profiles were identified via voxelwise models fit to passive listening responses. Attentional modulations were then quantified based on model predictions for attended and unattended stories in the cocktail-party task. We find that attention causes broad modulations at multiple levels of speech representations while growing stronger toward later stages of processing, and that unattended speech is represented up to the semantic level in parabelt auditory cortex. These results provide insights on attentional mechanisms that underlie the ability to selectively listen to a desired speaker in noisy multispeaker environments.

Breaking down the cocktail party: Attentional modulation of cerebral audiovisual speech processing

Recent studies utilizing electrophysiological speech envelope reconstruction have sparked renewed interest in the cocktail party effect by showing that auditory neurons entrain to selectively attended speech. Yet, the neural networks of attention to speech in naturalistic audiovisual settings with multiple sound sources remain poorly understood. We collected functional brain imaging data while participants viewed audiovisual video clips of lifelike dialogues with concurrent distracting speech in the background. Dialogues were presented in a full-factorial design, comprising task (listen to the dialogues vs. ignore them), audiovisual quality and semantic predictability. We used univariate analyses in combination with multivariate pattern analysis (MVPA) to study modulations of brain activity related to attentive processing of audiovisual speech. We found attentive speech processing to cause distinct spatiotemporal modulation profiles in distributed cortical areas including sensory and frontal-control networks. Semantic coherence modulated attention-related activation patterns in the earliest stages of auditory cortical processing, suggesting that the auditory cortex is involved in high-level speech processing. Our results corroborate views that emphasize the dynamic nature of attention, with task-specificity and context as cornerstones of the underlying neuro-cognitive mechanisms.

Modulation of Brain Activity by Selective Attention to Audiovisual Dialogues

In real-life noisy situations, we can selectively attend to conversations in the presence of irrelevant voices, but neurocognitive mechanisms in such natural listening situations remain largely unexplored. Previous research has shown distributed activity in the mid superior temporal gyrus (STG) and sulcus (STS) while listening to speech and human voices, in the posterior STS and fusiform gyrus when combining auditory, visual and linguistic information, as well as in left-hemisphere temporal and frontal cortical areas during comprehension. In the present functional magnetic resonance imaging (fMRI) study, we investigated how selective attention modulates neural responses to naturalistic audiovisual dialogues. Our healthy adult participants (N = 15) selectively attended to video-taped dialogues between a man and woman in the presence of irrelevant continuous speech in the background. We modulated the auditory quality of dialogues with noise vocoding and their visual quality by masking speech-related facial movements. Both increased auditory quality and increased visual quality were associated with bilateral activity enhancements in the STG/STS. In addition, decreased audiovisual stimulus quality elicited enhanced fronto-parietal activity, presumably reflecting increased attentional demands. Finally, attention to the dialogues, in relation to a control task where a fixation cross was attended and the dialogue ignored, yielded enhanced activity in the left planum polare, angular gyrus, the right temporal pole, as well as in the orbitofrontal/ventromedial prefrontal cortex and posterior cingulate gyrus. Our findings suggest that naturalistic conversations effectively engage participants and reveal brain networks related to social perception in addition to speech and semantic processing networks.

Tracking the Effects of Top-Down Attention on Word Discrimination Using Frequency-tagged Neuromagnetic Responses

Discrimination of words from nonspeech sounds is essential in communication. Still, how selective attention can influence this early step of speech processing remains elusive. To answer that question, brain activity was recorded with magnetoencephalography in 12 healthy adults while they listened to two sequences of auditory stimuli presented at 2.17 Hz, consisting of successions of one randomized word (tagging frequency = 0.54 Hz) and three acoustically matched nonverbal stimuli. Participants were instructed to focus their attention on the occurrence of a predefined word in the verbal attention condition and on a nonverbal stimulus in the nonverbal attention condition. Steady-state neuromagnetic responses were identified with spectral analysis at sensor and source levels. Significant sensor responses peaked at 0.54 and 2.17 Hz in both conditions. Sources at 0.54 Hz were reconstructed in supratemporal auditory cortex, left superior temporal gyrus (STG), left middle temporal gyrus, and left inferior frontal gyrus. Sources at 2.17 Hz were reconstructed in supratemporal auditory cortex and STG. Crucially, source strength in the left STG at 0.54 Hz was significantly higher in verbal attention than in nonverbal attention condition. This study demonstrates speech-sensitive responses at primary auditory and speech-related neocortical areas. Critically, it highlights that, during word discrimination, top-down attention modulates activity within the left STG. This area therefore appears to play a crucial role in selective verbal attentional processes for this early step of speech processing.

The functional and structural asymmetries of the superior temporal sulcus

The superior temporal sulcus (STS) is an anatomical structure that increasingly interests researchers. This structure appears to receive multisensory input and is involved in several perceptual and cognitive core functions, such as speech perception, audiovisual integration, (biological) motion processing and theory of mind capacities. In addition, the superior temporal sulcus is not only one of the longest sulci of the brain, but it also shows marked functional and structural asymmetries, some of which have only been found in humans. To explore the functional-structural relationships of these asymmetries in more detail, this study combines functional and structural magnetic resonance imaging. Using a speech perception task, an audiovisual integration task, and a theory of mind task, this study again demonstrated an involvement of the STS in these processes, with an expected strong leftward asymmetry for the speech perception task. Furthermore, this study confirmed the earlier described, human-specific asymmetries, namely that the left STS is longer than the right STS and that the right STS is deeper than the left STS. However, this study did not find any relationship between these structural asymmetries and the detected brain activations or their functional asymmetries. This can, on the other hand, give further support to the notion that the structural asymmetry of the STS is not directly related to the functional asymmetry of the speech perception and the language system as a whole, but that it may have other causes and functions.

Hemispheric association and dissociation of voice and speech information processing in stroke

As we listen to someone speaking, we extract both linguistic and non-linguistic information. Knowing how these two sets of information are processed in the brain is fundamental for the general understanding of social communication, speech recognition and therapy of language impairments. We investigated the pattern of performances in phoneme versus gender categorization in left and right hemisphere stroke patients, and found an anatomo-functional dissociation in the right frontal cortex, establishing a new syndrome in voice discrimination abilities. In addition, phoneme and gender performances were most often associated than dissociated in the left hemisphere patients, suggesting a common neural underpinnings.

Attention to natural auditory signals

The challenge of understanding how the brain processes natural signals is compounded by the fact that such signals are often tied closely to specific natural behaviors and natural environments. This added complexity is especially true for auditory communication signals that can carry information at multiple hierarchical levels, and often occur in the context of other competing communication signals. Selective attention provides a mechanism to focus processing resources on specific components of auditory signals, and simultaneously suppress responses to unwanted signals or noise. Although selective auditory attention has been well-studied behaviorally, very little is known about how selective auditory attention shapes the processing on natural auditory signals, and how the mechanisms of auditory attention are implemented in single neurons or neural circuits. Here we review the role of selective attention in modulating auditory responses to complex natural stimuli in humans. We then suggest how the current understanding can be applied to the study of selective auditory attention in the context natural signal processing at the level of single neurons and populations in animal models amenable to invasive neuroscience techniques. This article is part of a Special Issue entitled "Communication Sounds and the Brain: New Directions and Perspectives".

Stimulus-dependent activations and attention-related modulations in the auditory cortex: a meta-analysis of fMRI studies

We meta-analyzed 115 functional magnetic resonance imaging (fMRI) studies reporting auditory-cortex (AC) coordinates for activations related to active and passive processing of pitch and spatial location of non-speech sounds, as well as to the active and passive speech and voice processing. We aimed at revealing any systematic differences between AC surface locations of these activations by statistically analyzing the activation loci using the open-source Matlab toolbox VAMCA (Visualization and Meta-analysis on Cortical Anatomy). AC activations associated with pitch processing (e.g., active or passive listening to tones with a varying vs. fixed pitch) had median loci in the middle superior temporal gyrus (STG), lateral to Heschl's gyrus. However, median loci of activations due to the processing of infrequent pitch changes in a tone stream were centered in the STG or planum temporale (PT), significantly posterior to the median loci for other types of pitch processing. Median loci of attention-related modulations due to focused attention to pitch (e.g., attending selectively to low or high tones delivered in concurrent sequences) were, in turn, centered in the STG or superior temporal sulcus (STS), posterior to median loci for passive pitch processing. Activations due to spatial processing were centered in the posterior STG or PT, significantly posterior to pitch processing loci (processing of infrequent pitch changes excluded). In the right-hemisphere AC, the median locus of spatial attention-related modulations was in the STS, significantly inferior to the median locus for passive spatial processing. Activations associated with speech processing and those associated with voice processing had indistinguishable median loci at the border of mid-STG and mid-STS. Median loci of attention-related modulations due to attention to speech were in the same mid-STG/STS region. Thus, while attention to the pitch or location of non-speech sounds seems to recruit AC areas less involved in passive pitch or location processing, focused attention to speech predominantly enhances activations in regions that already respond to human vocalizations during passive listening. This suggests that distinct attention mechanisms might be engaged by attention to speech and attention to more elemental auditory features such as tone pitch or location. This article is part of a Special Issue entitled Human Auditory Neuroimaging.

Distinct cortical networks activated by auditory attention and working memory load

Auditory attention and working memory (WM) allow for selection and maintenance of relevant sound information in our minds, respectively, thus underlying goal-directed functioning in everyday acoustic environments. It is still unclear whether these two closely coupled functions are based on a common neural circuit, or whether they involve genuinely distinct subfunctions with separate neuronal substrates. In a full factorial functional MRI (fMRI) design, we independently manipulated the levels of auditory-verbal WM load and attentional interference using modified Auditory Continuous Performance Tests. Although many frontoparietal regions were jointly activated by increases of WM load and interference, there was a double dissociation between prefrontal cortex (PFC) subareas associated selectively with either auditory attention or WM. Specifically, anterior dorsolateral PFC (DLPFC) and the right anterior insula were selectively activated by increasing WM load, whereas subregions of middle lateral PFC and inferior frontal cortex (IFC) were associated with interference only. Meanwhile, a superadditive interaction between interference and load was detected in left medial superior frontal cortex, suggesting that in this area, activations are not only overlapping, but reflect a common resource pool recruited by increased attentional and WM demands. Indices of WM-specific suppression of anterolateral non-primary auditory cortices (AC) and attention-specific suppression of primary AC were also found, possibly reflecting suppression/interruption of sound-object processing of irrelevant stimuli during continuous task performance. Our results suggest a double dissociation between auditory attention and working memory in subregions of anterior DLPFC vs. middle lateral PFC/IFC in humans, respectively, in the context of substantially overlapping circuits.

Attention-related modulation of auditory-cortex responses to speech sounds during dichotic listening

Event-related magnetic fields (ERFs) were measured with magnetoencephalography (MEG) in fifteen healthy right-handed participants listening to sequences of consonant-vowel syllable pairs delivered dichotically (one syllable presented to the left ear and another syllable simultaneously to the right ear). The participants were instructed to press a response button to occurrences of a particular target syllable. In a condition with no other instruction (the non-forced condition, NF), they showed the well-known right-ear advantage (REA), that is, the participants responded more often to target syllables delivered to the right ear than to targets delivered to the left ear. The same was true in the forced-right (FR) condition, where the participants were instructed to attend selectively to the right-ear syllables and respond only to targets among them. In the forced-left (FL) condition, where they were instructed to respond only to left-ear targets, they responded more often to targets in this ear than to targets in the right ear. At 300-500 ms from syllable pair onset, a sustained field (SF) in ERFs to the syllable pairs was stronger in the left auditory cortex than in the right auditory cortex in the NF and FR conditions, while the opposite was true in the FL condition. Thus selective attention during dichotic listening leads to stronger processing of speech sounds in the auditory cortex contralateral to the attended direction. Our results also suggest that the REA observed for dichotic speech may involve a bias of attention to the right side even when there is no instruction to do so. This supports Kinsbourne's (1970) model of attention bias as a general principle of laterality.

Auditory attention—focusing the searchlight on sound

Some fifty years after the first physiological studies of auditory attention, the field is now ripening, with exciting recent insights into the psychophysics, psychology, and neural basis of auditory attention. Current research seeks to unravel the complex interactions of pre-attentive and attentive processing of the acoustic scene, the role of auditory attention in mediating receptive-field plasticity in both auditory spatial and auditory feature processing, the contrasts and parallels between auditory and visual attention pathways and mechanisms, the interplay of bottom-up and top-down attentional mechanisms, the influential role of attention, goals, and expectations in shaping auditory processing, and the orchestration of diverse attentional effects at multiple levels from the cochlea to the cortex.

Beyond superior temporal cortex: intersubject correlations in narrative speech comprehension

The role of superior temporal cortex in speech comprehension is well established, but the complete network of regions involved in understanding language in ecologically valid contexts is less clearly understood. In a functional magnetic resonance imaging (fMRI) study, we presented 24 subjects with auditory or audiovisual narratives, and used model-free intersubject correlational analyses to reveal brain areas that were modulated in a consistent way across subjects during the narratives. Conventional comparisons to a resting state were also performed. Both analyses showed the expected recruitment of superior temporal areas, however, the intersubject correlational analyses also revealed an extended network of areas involved in narrative speech comprehension. Two findings stand out in particular. Firstly, many areas in the "default mode" network (typically deactivated relative to rest) were systematically modulated by the time-varying properties of the auditory or audiovisual input. These areas included the anterior cingulate and adjacent medial frontal cortex, and the posterior cingulate and adjacent precuneus. Secondly, extensive bilateral inferior frontal and premotor regions were implicated in auditory as well as audiovisual language comprehension. This extended network of regions may be important for higher-level linguistic processes, and interfaces with extralinguistic cognitive, affective, and interpersonal systems.