Expectations boost the reconstruction of auditory features from electrophysiological responses to noisy speech.

Online speech processing imposes significant computational demands on the listening brain, the underlying mechanisms of which remain poorly understood. Here, we exploit the perceptual "pop-out" phenomenon (i.e. the dramatic improvement of speech intelligibility after receiving information about speech content) to investigate the neurophysiological effects of prior expectations on degraded speech comprehension. We recorded electroencephalography (EEG) and pupillometry from 21 adults while they rated the clarity of noise-vocoded and sine-wave synthesized sentences. Pop-out was reliably elicited following visual presentation of the corresponding written sentence, but not following incongruent or neutral text. Pop-out was associated with improved reconstruction of the acoustic stimulus envelope from low-frequency EEG activity, implying that improvements in perceptual clarity were mediated via top-down signals that enhanced the quality of cortical speech representations. Spectral analysis further revealed that pop-out was accompanied by a reduction in theta-band power, consistent with predictive coding accounts of acoustic filling-in and incremental sentence processing. Moreover, delta-band power, alpha-band power, and pupil diameter were all increased following the provision of any written sentence information, irrespective of content. Together, these findings reveal distinctive profiles of neurophysiological activity that differentiate the content-specific processes associated with degraded speech comprehension from the context-specific processes invoked under adverse listening conditions.

Infants ask for help when they know they don't know.

Uncertainty monitoring is a core property of metacognition, allowing individuals to adapt their decision-making strategies depending on the state of their knowledge. Although it has been argued that other animals share these metacognitive abilities, only humans seem to possess the ability to explicitly communicate their own uncertainty to others. It remains unknown whether this capacity is present early in development, or whether it emerges later with the ability to verbally report one's own mental states. Here, using a nonverbal memory-monitoring paradigm, we show that 20-month-olds can monitor and report their own uncertainty. Infants had to remember the location of a hidden toy before pointing to indicate where they wanted to recover it. In an experimental group, infants were given the possibility to ask for help through nonverbal communication when they had forgotten the toy location. Compared with a control group in which infants had no other option but to decide by themselves, infants given the opportunity to ask for help used this option strategically to improve their performance. Asking for help was used selectively to avoid making errors and to decline difficult choices. These results demonstrate that infants are able to successfully monitor their own uncertainty and share this information with others to fulfill their goals.

Neural Markers of Responsiveness to the Environment in Human Sleep.

UNLABELLED: Sleep is characterized by a loss of behavioral responsiveness. However, recent research has shown that the sleeping brain is not completely disconnected from its environment. How neural activity constrains the ability to process sensory information while asleep is yet unclear. Here, we instructed human volunteers to classify words with lateralized hand responses while falling asleep. Using an electroencephalographic (EEG) marker of motor preparation, we show how responsiveness is modulated across sleep. These modulations are tracked using classic event-related potential analyses complemented by Lempel-Ziv complexity (LZc), a measure shown to track arousal in sleep and anesthesia. Neural activity related to the semantic content of stimuli was conserved in light non-rapid eye movement (NREM) sleep. However, these processes were suppressed in deep NREM sleep and, importantly, also in REM sleep, despite the recovery of wake-like neural activity in the latter. In NREM sleep, sensory activations were counterbalanced by evoked down states, which, when present, blocked further processing of external information. In addition, responsiveness markers correlated positively with baseline complexity, which could be related to modulation in sleep depth. In REM sleep, however, this relationship was reversed. We therefore propose that, in REM sleep, endogenously generated processes compete with the processing of external input. Sleep can thus be seen as a self-regulated process in which external information can be processed in lighter stages but suppressed in deeper stages. Last, our results suggest drastically different gating mechanisms in NREM and REM sleep. SIGNIFICANCE STATEMENT: Previous research has tempered the notion that sleepers are isolated from their environment. Here, we pushed this idea forward and examined, across all sleep stages, the brain's ability to flexibly process sensory information, up to the decision level. We extracted an EEG marker of motor preparation to determine the completion of the sensory processing chain and explored how it is constrained by baseline and evoked neural activity. In NREM sleep, slow waves elicited by stimuli appeared to block response preparation. We also used a novel analytic approach (Lempel-Ziv complexity) and showed that the ability to process external information correlates with neural complexity. A reversal of the correlation between complexity and motor indices in REM sleep suggests drastically different gating mechanisms across sleep stages.

Prior expectations modulate unconscious evidence accumulation.

Unconscious processes have been shown to affect both perception and behaviour. However, the flexibility of such processes remains unknown. Here we investigate whether unconscious decisional processes can adapt to the utility of sensory information. To this end, we had participants gradually accumulate information from noisy motion stimuli, until a decision was reached. We titrated conscious awareness of these stimuli by simultaneously presenting a dynamic dichoptic mask. Crucially, we manipulated the likelihood that the suppressed portion of each presentation would contain useful information. Our results show that the statistics of the environment can be used to modulate unconscious evidence accumulation, resulting in faster choices. Furthermore, computational modelling revealed that this modulation is due to a change in the quality of unconscious evidence accumulation, rather than a conscious change in strategy. Together, these results indicate that unconscious decisional mechanisms are capable of optimising performance by flexibly adapting to the statistical environment.

Spontaneous Activity Patterns in Primary Visual Cortex Predispose to Visual Hallucinations.

According to theoretical frameworks casting perception as inference, vision results from the integration of bottom-up visual input with top-down expectations. Under conditions of strongly degraded sensory input, this may occasionally result in false perceptions in the absence of a sensory signal, also termed "hallucinations." Here, we investigated whether spontaneous prestimulus activity patterns in sensory circuits, which may embody a participant's prior expectations, predispose the observer toward false perceptions. Specifically, we used fMRI to investigate whether the representational content of prestimulus activity in early visual cortex is linked to subsequent perception during a challenging detection task. Human participants were asked to detect oriented gratings of a particular orientation that were embedded in noise. We found two characteristics of prestimulus activity that predisposed participants to hallucinations: overall lower prestimulus activity and a bias in the prestimulus activity patterns toward the to-be-detected (expected) grating. These results suggest that perceptual hallucinations may be due to an imprecise and biased state of sensory circuits preceding sensory evidence collection. SIGNIFICANCE STATEMENT: When sensory stimulation is strongly degraded, we occasionally misperceive a stimulus when only noise is present: a perceptual hallucination. Using fMRI in healthy participants, we investigated whether the state of early visual cortex preceding stimulus onset predisposes an observer to hallucinations. We found two characteristics of prestimulus activity that predisposed participants to hallucinations: overall lower prestimulus activity and a bias in the prestimulus activity patterns toward the expected grating. These results suggest that perceptual hallucinations are due to an imprecise and biased state of sensory circuits preceding sensation.

Nonconscious learning from crowded sequences.

Can people learn complex information without conscious awareness? Implicit learning-learning without awareness of what has been learned-has been the focus of intense investigation over the last 50 years. However, it remains controversial whether complex knowledge can be learned implicitly. In the research reported here, we addressed this challenge by asking participants to differentiate between sequences of symbols they could not perceive consciously. Using an operant-conditioning task, we showed that participants learned to associate distinct sequences of crowded (nondiscriminable) symbols with their respective monetary outcomes (reward or punishment). Overall, our study demonstrates that sensitivity to sequential regularities can arise through the nonconscious temporal integration of perceptual information.

The role of spatial switching in the attentional blink.

The attentional blink (AB) is a well-established paradigm in which identification of a target T2 is reduced shortly after presentation of an earlier target T1. An important question concerns the importance of backward masking during the AB. While task switching has been found to be a strong modulator mediating the AB without any masking of T2, the present study investigated whether spatial switching could similarly produce an AB without masking. Using a spatial AB paradigm in which items appeared at different locations; we found (a) a significant AB without backward masking of T2 but no AB when no distractors followed T2, (b) no evidence for Lag 1 sparing. These findings show that when there is a spatial switch between the targets, presenting the distractor following T2 at the same location than T2 (backward masking) is not a necessary condition for the AB to occur, but T2 has to be followed by surrounding distractors (appearing at different locations than T2). This pattern of data confirms that spatial switching is a robust modulator of the AB, but to a less extent than task switching.

Acceleration of information processing en route to perceptual awareness in infancy.

Electrophysiological studies1-6 have suggested an acceleration in information processing in the first years of life, probably largely caused by the progressive myelination of the cortex.7,8 Here, we ask whether and how this acceleration affects information processes that contribute to perceptual awareness. We addressed this issue leveraging on the attentional blink phenomenon9,10 in infants,11 children, and adult participants. When two visual targets (T1 and T2) are to be detected, the observer often misses T2, if it appears shortly after T1, as if the observer's attention blinked. This phenomenon is explained by the two-stage model of perception, where an early unconscious sensory stage is followed by a late and central stage that relies on limited attentional resources.9-14 Although both T1 and T2 are processed in the earlier sensory stage, the capacity limits of the second stage are such that T2 cannot be processed as long as attention is occupied by T1.9-13 The duration of the attentional blink, thus, indexes the speed of the late processing stage of visual stimuli, which is associated with perceptual awareness.12-14 Indeed, in adults, the blink only occurs if T1 is consciously perceived but not when it is missed or processed subliminally.15 Accordingly, neuroimaging studies16-18 have shown that late processes blocked by T1 involve frontoparietal areas, thought to be responsible for global cognitive availability, conscious access, and reportability.19 Here, we show that the attentional blink is present in young infants, suggesting that the two-stage organization of perception is in place at 5 and 8 months of age. In addition, we show that the duration of the attentional blink shrinks with development, suggesting that a fundamental aspect of cognitive development is the fast acceleration of the late processing stage of perception.

Learning New Vocabulary Implicitly During Sleep Transfers With Cross-Modal Generalization Into Wakefulness.

New information can be learned during sleep but the extent to which we can access this knowledge after awakening is far less understood. Using a novel Associative Transfer Learning paradigm, we show that, after hearing unknown Japanese words with sounds referring to their meaning during sleep, participants could identify the images depicting the meaning of newly acquired Japanese words after awakening (N = 22). Moreover, we demonstrate that this cross-modal generalization is implicit, meaning that participants remain unaware of this knowledge. Using electroencephalography, we further show that frontal slow-wave responses to auditory stimuli during sleep predicted memory performance after awakening. This neural signature of memory formation gradually emerged over the course of the sleep phase, highlighting the dynamics of associative learning during sleep. This study provides novel evidence that the formation of new associative memories can be traced back to the dynamics of slow-wave responses to stimuli during sleep and that their implicit transfer into wakefulness can be generalized across sensory modalities.

Preference is biased by crowded facial expressions.

Crowding occurs when nearby flankers impede the identification of a peripheral stimulus. Here, we studied whether crowded features containing inaccessible emotional information can nevertheless affect preference judgments. We relied on gaze-contingent crowding, a novel method allowing for constant perceptual unawareness through eye-tracking control, and we found that crowded facial expressions can bias evaluative judgments of neutral pictographs. Furthermore, this emotional bias was effective not only for static images of faces, but also for videos displaying dynamic facial expressions. In addition to showing an alternative approach for probing nonconscious cognition, this study reveals that crowded information, instead of being fully suppressed, can have important influences on decisions.

Neural control of cross-language asymmetry in the bilingual brain.

Most bilinguals understand their second language more slowly than their first. This behavioral asymmetry may arise from the perceptual, phonological, lexicosemantic, or strategic components of bilingual word processing. However, little is known about the neural source of such language dominance and how it is regulated in the bilingual brain. Using functional magnetic resonance imaging, we found that unconscious neural priming in bilingual word recognition is language nonselective in the left midfusiform gyrus but exhibits a preference for the dominant language in the left posterior middle temporal gyrus (MTG). These early-stage components of reading were located slightly upstream of the left midlateral MTG, which exhibited enhanced response during a conscious switch of language. Effective connectivity analysis revealed that this language switch is triggered by reentrant signals from inferior frontal cortex and not by bottom-up signals from occipitotemporal cortex. We further confirmed that magnetic stimulation of the same inferior frontal region interferes with conscious language control but does not disrupt unconscious priming by masked words. Collectively, our results demonstrate that the neural bottleneck in the bilingual brain is a cross-language asymmetry of form-meaning association in inferolateral temporal cortex, which is overcome by a top-down cognitive control for implementing a task schema in each language.

Perceptual awareness and categorical representation of faces: evidence from masked priming.

How internal categories influence how we perceive the world is a fundamental question in cognitive sciences. Yet, the relation between perceptual awareness and perceptual categorization has remained largely uncovered so far. Here, we addressed this question by focusing on face perception during subliminal and conscious perception. We used morphed continua between two face identities and we assessed, through a masked priming paradigm, the perceptual processing of these morphed faces under subliminal and supraliminal conditions. We found that priming from subliminal faces followed linearly the information present in the primes, while priming from visible faces revealed a non-linear profile, indicating a categorical processing of face identities. Our results thus point to a special relation between perceptual awareness and categorical processing of faces, and support the dissociation between two modes of information processing: a subliminal mode involving analog treatment of stimuli information, and a supraliminal mode relying on discrete representation.

Multi-feature objects elicit nonconscious priming despite crowding.

The conscious representation we build from the visual environment appears jumbled in the periphery, reflecting a phenomenon known as crowding. Yet, it remains possible that object-level representations (i.e., resulting from the binding of the stimulus' different features) are preserved even if they are not consciously accessible. With a paradigm involving gaze-contingent substitution, which allows us to ensure the constant absence of peripheral stimulus discrimination, we show that, despite their jumbled appearance, multi-feature crowded objects, such as faces and directional symbols, are encoded in a nonconscious manner and can influence subsequent behavior. Furthermore, we show that the encoding of complex crowded contents is modulated by attention in the absence of consciousness. These results, in addition to bringing new insights concerning the fate of crowded information, illustrate the potential of the Gaze-Contingent Crowding (GCC) approach for probing nonconscious cognition.

Increased sensory evidence reverses nonconscious priming during crowding.

Sensory adaptation reflects the fact that the responsiveness of a perceptual system changes after the processing of a specific stimulus. Two manifestations of this property have been used in order to infer the mechanisms underlying vision: priming, in which the processing of a target is facilitated by prior exposure to a related adaptor, and habituation, in which this processing is hurt by overexposure to an adaptor. In the present study, we investigated the link between priming and habituation by measuring how sensory evidence (short vs. long adaptor exposure) and perceptual awareness (discriminable vs. undiscriminable adaptor stimulus) affects the adaptive response on a related target. Relying on gaze-contingent crowding, we manipulated independently adaptor discriminability and adaptor duration and inferred sensory adaptation from reaction times on the discrimination of a subsequent oriented target. When adaptor orientation was undiscriminable, we found that increasing its duration reversed priming into habituation. When adaptor orientation was discriminable, priming effects were larger after short exposure, but increasing adaptor duration led to a decrease of priming instead of a reverse into habituation. We discuss our results as reflecting changes in the temporal dynamics of angular orientation processing, depending on the mechanisms associated with perceptual awareness and attentional amplification.

People confabulate with high confidence when their decisions are supported by weak internal variables.

People can introspect on their internal state and report the reasons driving their decisions but choice blindness (CB) experiments suggest that this ability can sometimes be a retrospective illusion. Indeed, when presented with deceptive cues, people justify choices they did not make in the first place, suggesting that external cues largely contribute to introspective processes. Yet, it remains unclear what are the respective contributions of external cues and internal decision variables in forming introspective report. Here, using a brain-computer interface, we show that internal variables continue to be monitored but are less impactful than deceptive external cues during CB episodes. Moreover, we show that deceptive cues overturn the classical relationship between confidence and accuracy: introspective failures are associated with higher confidence than genuine introspective reports. We tracked back the origin of these overconfident confabulations by revealing their prominence when internal decision evidence is weak and variable. Thus, introspection is neither a direct reading of internal variables nor a mere retrospective illusion, but rather reflects the integration of internal decision evidence and external cues, with CB being a special instance where internal evidence is inconsistent.

Task-guided selection of the dual neural pathways for reading.

The visual perception of words is known to activate the auditory representation of their spoken forms automatically. We examined the neural mechanism for this phonological activation using transcranial magnetic stimulation (TMS) with a masked priming paradigm. The stimulation sites (left superior temporal gyrus [L-STG] and inferior parietal lobe [L-IPL]), modality of targets (visual and auditory), and task (pronunciation and lexical decision) were manipulated independently. For both within- and cross-modal conditions, the repetition priming during pronunciation was eliminated when TMS was applied to the L-IPL, but not when applied to the L-STG, whereas the priming during lexical decision was eliminated when the L-STG, but not the L-IPL, was stimulated. The observed double dissociation suggests that the conscious task instruction modulates the stimulus-driven activation of the lateral temporal cortex for lexico-phonological activation and the inferior parietal cortex for spoken word production, and thereby engages a different neural network for generating the appropriate behavioral response.

Cerebral bases of subliminal speech priming.

While the neural correlates of unconscious perception and subliminal priming have been largely studied for visual stimuli, little is known about their counterparts in the auditory modality. Here we used a subliminal speech priming method in combination with fMRI to investigate which regions of the cerebral network for language can respond in the absence of awareness. Participants performed a lexical decision task on target items preceded by subliminal primes, which were either phonetically identical or different from the target. Moreover, the prime and target could be spoken by the same speaker or by two different speakers. Word repetition reduced the activity in the insula and in the left superior temporal gyrus. Although the priming effect on reaction times was independent of voice manipulation, neural repetition suppression was modulated by speaker change in the superior temporal gyrus while the insula showed voice-independent priming. These results provide neuroimaging evidence of subliminal priming for spoken words and inform us on the first, unconscious stages of speech perception.

How spatial frequencies and visual awareness interact during face processing.

In vision, high and low spatial frequencies have been dissociated at the cognitive and neural levels. Usually, high spatial frequency (HSF) is associated with slow analysis along the ventral cortical stream, and low spatial frequency (LSF) is associated with fast and automatic processing. These findings suggest a specific relation between spatial-frequency processing and visual awareness. We investigated this issue using masked-face priming with hybrid prime images of variable visibility. We found subliminal priming for both LSF and HSF information, along with a strong interaction between spatial frequency and visibility: HSF-related priming increased with stimulus visibility, whereas LSF influences remained unchanged. We argue that the results limit the validity of the coarse-to-fine model of vision and of models equating ventral-stream activity with perceptual awareness. Interpreting our results in light of the diagnostic approach suggests a close relation between awareness and diagnosticity.

Activity in face-responsive brain regions is modulated by invisible, attended faces: evidence from masked priming.

It is often assumed that neural activity in face-responsive regions of primate cortex correlates with conscious perception of faces. However, whether such activity occurs without awareness is still debated. Using functional magnetic resonance imaging (fMRI) in conjunction with a novel masked face priming paradigm, we observed neural modulations that could not be attributed to perceptual awareness. More specifically, we found reduced activity in several classic face-processing regions, including the "fusiform face area," "occipital face area," and superior temporal sulcus, when a face was preceded by a briefly flashed image of the same face, relative to a different face, even when 2 images of the same face differed. Importantly, unlike most previous studies, which have minimized awareness by using conditions of inattention, the present results occurred when the stimuli (the primes) were attended. By contrast, when primes were perceived consciously, in a long-lag priming paradigm, we found repetition-related activity increases in additional frontal and parietal regions. These data not only demonstrate that fMRI activity in face-responsive regions can be modulated independently of perceptual awareness, but also document where such subliminal face-processing occurs (i.e., restricted to face-responsive regions of occipital and temporal cortex) and to what extent (i.e., independent of the specific image).

Task-specific change of unconscious neural priming in the cerebral language network.

We explored the impact of task context on subliminal neural priming using functional magnetic resonance imaging. The repetition of words during semantic categorization produced activation reduction in the left middle temporal gyrus previously associated with semantic-level representation and dorsal premotor cortex. By contrast, reading aloud produced repetition enhancement in the left inferior parietal lobe associated with print-to-sound conversion and ventral premotor cortex. Analyses of effective connectivity revealed that the task set for reading generated reciprocal excitatory connections between the left inferior parietal and superior temporal regions, reflecting the audiovisual integration required for vocalization, whereas categorization did not produce such backward projection to posterior regions. Thus, masked repetition priming involves two distinct components in the task-specific neural streams, one in the parietotemporal cortex for task-specific word processing and the other in the premotor cortex for behavioral response preparation. The top-down influence of task sets further changes the directions of the unconscious priming in the entire cerebral circuitry for reading.