Publications of year 2015
  1. Mélanie Strauss. Using Magneto-encephalography to Assess the Processing Depth of Auditory Stimuli in the Sleeping Human Brain.. PhD thesis, Paris V, 2015. [bibtex-entry]

Book chapters
  1. Jessica Dubois and Ghislaine Dehaene-Lambertz. Fetal and Postnatal Development of the Cortex: MRI and Genetics. In Arthur W. Toga, editor,Brain Mapping: An Encyclopedic Reference, volume 2, pages 11-19. Academic Press: Elsevier, 2015. [PDF] [bibtex-entry]

  2. Jessica Dubois, Ivica Kostovic, and Milos Judas. Development of Structural and Functional Connectivity. In Arthur W. Toga, editor,Brain Mapping: An Encyclopedic Reference, volume 2, pages 423-437. Academic Press: Elsevier., 2015. [PDF] [bibtex-entry]

Articles in journals
  1. Sami Abboud, Shachar Maidenbaum, Stanislas Dehaene, and Amir Amedi. A number-form area in the blind.. Nat Commun, 6:6026, 2015. [WWW] [PDF]
    Abstract: Distinct preference for visual number symbols was recently discovered in the human right inferior temporal gyrus (rITG). It remains unclear how this preference emerges, what is the contribution of shape biases to its formation and whether visual processing underlies it. Here we use congenital blindness as a model for brain development without visual experience. During fMRI, we present blind subjects with shapes encoded using a novel visual-to-music sensory-substitution device (The EyeMusic). Greater activation is observed in the rITG when subjects process symbols as numbers compared with control tasks on the same symbols. Using resting-state fMRI in the blind and sighted, we further show that the areas with preference for numerals and letters exhibit distinct patterns of functional connectivity with quantity and language-processing areas, respectively. Our findings suggest that specificity in the ventral 'visual' stream can emerge independently of sensory modality and visual experience, under the influence of distinct connectivity patterns.

  2. Pablo Barttfeld, Lynn Uhrig, Jacobo D. Sitt, Mariano Sigman, Béchir Jarraya, and Stanislas Dehaene. Signature of consciousness in the dynamics of resting-state brain activity.. Proc Natl Acad Sci U S A, 112(3):887--892, January 2015. [WWW] [PDF]
    Abstract: At rest, the brain is traversed by spontaneous functional connectivity patterns. Two hypotheses have been proposed for their origins: they may reflect a continuous stream of ongoing cognitive processes as well as random fluctuations shaped by a fixed anatomical connectivity matrix. Here we show that both sources contribute to the shaping of resting-state networks, yet with distinct contributions during consciousness and anesthesia. We measured dynamical functional connectivity with functional MRI during the resting state in awake and anesthetized monkeys. Under anesthesia, the more frequent functional connectivity patterns inherit the structure of anatomical connectivity, exhibit fewer small-world properties, and lack negative correlations. Conversely, wakefulness is characterized by the sequential exploration of a richer repertoire of functional configurations, often dissimilar to anatomical structure, and comprising positive and negative correlations among brain regions. These results reconcile theories of consciousness with observations of long-range correlation in the anesthetized brain and show that a rich functional dynamics might constitute a signature of consciousness, with potential clinical implications for the detection of awareness in anesthesia and brain-lesioned patients.

  3. Claire H C. Chang, Christophe Pallier, Denise H. Wu, Kimihiro Nakamura, Antoinette Jobert, W-J. Kuo, and Stanislas Dehaene. Adaptation of the human visual system to the statistics of letters and line configurations.. Neuroimage, July 2015. [WWW] [PDF]
    Abstract: By adulthood, literate humans have been exposed to millions of visual scenes and pages of text. Does the human visual system become attuned to the statistics of its inputs? Using functional magnetic resonance imaging, we examined whether the brain responses to line configurations are proportional to their natural-scene frequency. To further distinguish prior cortical competence from adaptation induced by learning to read, we manipulated whether the selected configurations formed letters and whether they were presented on the horizontal meridian, the familiar location where words usually appear, or on the vertical meridian. While no natural-scene frequency effect was observed, we observed letter-status and letter frequency effects on bilateral occipital activation, mainly for horizontal stimuli. The findings suggest a reorganization of the visual pathway resulting from reading acquisition under genetic and connectional constraints. Even early retinotopic areas showed a stronger response to letters than to rotated versions of the same shapes, suggesting an early visual tuning to large visual features such as letters.

  4. Stanislas Dehaene, Laurent Cohen, José Morais, and Régine Kolinsky. Illiterate to literate: behavioural and cerebral changes induced by reading acquisition. Nat Rev Neurosci, 16(4):234--244, April 2015. [WWW] [PDF]
    Abstract: The acquisition of literacy transforms the human brain. By reviewing studies of illiterate subjects, we propose specific hypotheses on how the functions of core brain systems are partially reoriented or 'recycled' when learning to read. Literacy acquisition improves early visual processing and reorganizes the ventral occipito-temporal pathway: responses to written characters are increased in the left occipito-temporal sulcus, whereas responses to faces shift towards the right hemisphere. Literacy also modifies phonological coding and strengthens the functional and anatomical link between phonemic and graphemic representations. Literacy acquisition therefore provides a remarkable example of how the brain reorganizes to accommodate a novel cultural skill.

  5. Stanislas Dehaene, Yadin Dudai, and Christina Konen. Cognitive Architectures. Neuron, Volume 88, Issue 1, 7 October 2015:1, 2015. [WWW] [PDF] [bibtex-entry]

  6. Stanislas Dehaene, Florent Meyniel, Catherine Wacongne, Liping Wang, and Christophe Pallier. The Neural Representation of Sequences: From Transition Probabilities to Algebraic Patterns and Linguistic Trees.. Neuron, 88(1):2--19, October 2015. [WWW] [PDF]
    Abstract: A sequence of images, sounds, or words can be stored at several levels of detail, from specific items and their timing to abstract structure. We propose a taxonomy of five distinct cerebral mechanisms for sequence coding: transitions and timing knowledge, chunking, ordinal knowledge, algebraic patterns, and nested tree structures. In each case, we review the available experimental paradigms and list the behavioral and neural signatures of the systems involved. Tree structures require a specific recursive neural code, as yet unidentified by electrophysiology, possibly unique to humans, and which may explain the singularity of human language and cognition.

  7. G Dehaene-Lambertz and E. Spelke. The Infancy of the Human Brain. Neuron, Volume 88, Issue 1, 7 October 2015:93-109, 2015. [WWW] [PDF] [bibtex-entry]

  8. Jessica Dubois, Cyril Poupon, Bertrand Thirion, Hina Simonnet, Sofya Kulikova, François Leroy, Lucie Hertz-Pannier, and Ghislaine Dehaene-Lambertz. Exploring the Early Organization and Maturation of Linguistic Pathways in the Human Infant Brain.. Cereb Cortex, April 2015. [WWW] [PDF]
    Abstract: Linguistic processing is based on a close collaboration between temporal and frontal regions connected by two pathways: the "dorsal" and "ventral pathways" (assumed to support phonological and semantic processing, respectively, in adults). We investigated here the development of these pathways at the onset of language acquisition, during the first post-natal weeks, using cross-sectional diffusion imaging in 21 healthy infants (6-22 weeks of age) and 17 young adults. We compared the bundle organization and microstructure at these two ages using tractography and original clustering analyses of diffusion tensor imaging parameters. We observed structural similarities between both groups, especially concerning the dorsal/ventral pathway segregation and the arcuate fasciculus asymmetry. We further highlighted the developmental tempos of the linguistic bundles: The ventral pathway maturation was more advanced than the dorsal pathway maturation, but the latter catches up during the first post-natal months. Its fast development during this period might relate to the learning of speech cross-modal representations and to the first combinatorial analyses of the speech input.

  9. Denis A. Engemann and Alexandre Gramfort. Automated model selection in covariance estimation and spatial whitening of MEG and EEG signals. Neuroimage, 108:328--342, March 2015. [WWW] [PDF]
    Abstract: Magnetoencephalography and electroencephalography (M/EEG) measure non-invasively the weak electromagnetic fields induced by post-synaptic neural currents. The estimation of the spatial covariance of the signals recorded on M/EEG sensors is a building block of modern data analysis pipelines. Such covariance estimates are used in brain-computer interfaces (BCI) systems, in nearly all source localization methods for spatial whitening as well as for data covariance estimation in beamformers. The rationale for such models is that the signals can be modeled by a zero mean Gaussian distribution. While maximizing the Gaussian likelihood seems natural, it leads to a covariance estimate known as empirical covariance (EC). It turns out that the EC is a poor estimate of the true covariance when the number of samples is small. To address this issue the estimation needs to be regularized. The most common approach downweights off-diagonal coefficients, while more advanced regularization methods are based on shrinkage techniques or generative models with low rank assumptions: probabilistic PCA (PPCA) and factor analysis (FA). Using cross-validation all of these models can be tuned and compared based on Gaussian likelihood computed on unseen data. We investigated these models on simulations, one electroencephalography (EEG) dataset as well as magnetoencephalography (MEG) datasets from the most common MEG systems. First, our results demonstrate that different models can be the best, depending on the number of samples, heterogeneity of sensor types and noise properties. Second, we show that the models tuned by cross-validation are superior to models with hand-selected regularization. Hence, we propose an automated solution to the often overlooked problem of covariance estimation of M/EEG signals. The relevance of the procedure is demonstrated here for spatial whitening and source localization of MEG signals.

  10. Alice Gomez, Manuela Piazza, Antoinette Jobert, Ghislaine Dehaene-Lambertz, Stanislas Dehaene, and Caroline Huron. Mathematical difficulties in developmental coordination disorder: Symbolic and nonsymbolic number processing.. Res Dev Disabil, 43-44:167--178, 2015. [WWW]
    Abstract: At school, children with Developmental Coordination Disorder (DCD) struggle with mathematics. However, little attention has been paid to their numerical cognition abilities. The goal of this study was to better understand the cognitive basis for mathematical difficulties in children with DCD. Twenty 7-to-10 years-old children with DCD were compared to twenty age-matched typically developing children using dot and digit comparison tasks to assess symbolic and nonsymbolic number processing and in a task of single digits additions. Results showed that children with DCD had lower performance in nonsymbolic and symbolic number comparison tasks than typically developing children. They were also slower to solve simple addition problems. Moreover, correlational analyses showed that children with DCD who experienced greater impairments in the nonsymbolic task also performed more poorly in the symbolic tasks. These findings suggest that DCD impairs both nonsymbolic and symbolic number processing. A systematic assessment of numerical cognition in children with DCD could provide a more comprehensive picture of their deficits and help in proposing specific remediation.

  11. Thomas Hannagan, Amir Amedi, Laurent Cohen, Ghislaine Dehaene-Lambertz, and Stanislas Dehaene. Origins of the specialization for letters and numbers in ventral occipitotemporal cortex. Trends Cogn Sci, June 2015. [WWW]
    Abstract: Deep in the occipitotemporal cortex lie two functional regions, the visual word form area (VWFA) and the number form area (NFA), which are thought to play a special role in letter and number recognition, respectively. We review recent progress made in characterizing the origins of these symbol form areas in children or adults, sighted or blind subjects, and humans or monkeys. We propose two non-mutually-exclusive hypotheses on the origins of the VWFA and NFA: the presence of a connectivity bias, and a sensitivity to shape features. We assess the explanatory power of these hypotheses, describe their consequences, and offer several experimental tests.

  12. Yi-Hui Hung, Christophe Pallier, Stanislas Dehaene, Yi-Chen Lin, Acer Chang, Ovid J-L. Tzeng, and Denise H. Wu. Neural correlates of merging number words.. Neuroimage, 122:33--43, July 2015. [WWW]
    Abstract: Complex number words (e.g., "twenty two") are formed by merging together several simple number words (e.g., "twenty" and "two"). In the present study, we explored the neural correlates of this operation and investigated to what extent it engages brain areas involved processing numerical quantity and linguistic syntactic structure. Participants speaking two typologically distinct languages, French and Chinese, were required to read aloud sequences of simple number words while their cerebral activity was recorded by functional magnetic resonance imaging. Each number word could either be merged with the previous ones (e.g., 'twenty three') or not (e.g., 'three twenty'), thus forming four levels ranging from lists of number words to complex numerals. When a number word could be merged with the preceding ones, it was named faster than when it could not. Neuroimaging results showed that the number of merges correlated with activation in the left inferior frontal gyrus and in the left inferior parietal lobule. Consistent findings across Chinese and French participants suggest that these regions serve as the neural bases for forming complex number words in different languages.

  13. A. L. Jouen, T. M. Ellmore, C. J. Madden, C. Pallier, P. F. Dominey, and J. Ventre-Dominey. Beyond the word and image: characteristics of a common meaning system for language and vision revealed by functional and structural imaging.. Neuroimage, 106:72--85, February 2015. [WWW]
    Abstract: This research tests the hypothesis that comprehension of human events will engage an extended semantic representation system, independent of the input modality (sentence vs. picture). To investigate this, we examined brain activation and connectivity in 19 subjects who read sentences and viewed pictures depicting everyday events, in a combined fMRI and DTI study. Conjunction of activity in understanding sentences and pictures revealed a common fronto-temporo-parietal network that included the middle and inferior frontal gyri, the parahippocampal-retrosplenial complex, the anterior and middle temporal gyri, the inferior parietal lobe in particular the temporo-parietal cortex. DTI tractography seeded from this temporo-parietal cortex hub revealed a multi-component network reaching into the temporal pole, the ventral frontal pole and premotor cortex. A significant correlation was found between the relative pathway density issued from the temporo-parietal cortex and the imageability of sentences for individual subjects, suggesting a potential functional link between comprehension and the temporo-parietal connectivity strength. These data help to define a "meaning" network that includes components of recently characterized systems for semantic memory, embodied simulation, and visuo-spatial scene representation. The network substantially overlaps with the "default mode" network implicated as part of a core network of semantic representation, along with brain systems related to the formation of mental models, and reasoning. These data are consistent with a model of real-world situational understanding that is highly embodied. Crucially, the neural basis of this embodied understanding is not limited to sensorimotor systems, but extends to the highest levels of cognition, including autobiographical memory, scene analysis, mental model formation, reasoning and theory of mind.

  14. C. Kabdebon, M. Pena, M. Buiatti, and G. Dehaene-Lambertz. Electrophysiological evidence of statistical learning of long-distance dependencies in 8-month-old preterm and full-term infants.. Brain Lang, 148:25--36, September 2015. [WWW] [PDF]
    Abstract: Using electroencephalography, we examined 8-month-old infants' ability to discover a systematic dependency between the first and third syllables of successive words, concatenated into a monotonous speech stream, and to subsequently generalize this regularity to new items presented in isolation. Full-term and preterm infants, while exposed to the stream, displayed a significant entrainment (phase-locking) to the syllabic and word frequencies, demonstrating that they were sensitive to the word unit. The acquisition of the systematic dependency defining words was confirmed by the significantly different neural responses to rule-words and part-words subsequently presented during the test phase. Finally, we observed a correlation between syllabic entrainment during learning and the difference in phase coherence between the test conditions (rule-words vs part-words) suggesting that temporal processing of the syllable unit might be crucial in linguistic learning. No group difference was observed suggesting that non-adjacent statistical computations are already robust at 8months, even in preterm infants, and thus develop during the first year of life, earlier than expected from behavioral studies.

  15. J. Katz, E. Chemla, and C Pallier. An Attentional Effect of Musical Metrical Structure. Plos One, 2015. [WWW] [bibtex-entry]

  16. J Lebenberg, C Poupon, B Thirion, F Leroy, JF Mangin, G Dehaene-Lambertz, and J Dubois. Clustering the infant brain tissues based on microstructural properties and maturation assessment using multi-parametric MRI. IEEE ISBI, DOI 10.1109/ISBI.2015.7163837:148-151, 2015. [PDF] [bibtex-entry]

  17. Julien Lefèvre, David Germanaud, Jessica Dubois, François Rousseau, Ines de Macedo Santos, Hugo Angleys, Jean-François Mangin, Petra S. Hüppi, Nadine Girard, and François De Guio. Are Developmental Trajectories of Cortical Folding Comparable Between Cross-sectional Datasets of Fetuses and Preterm Newborns?. Cereb Cortex, June 2015. [WWW] [PDF]
    Abstract: Magnetic resonance imaging has proved to be suitable and efficient for in vivo investigation of the early process of brain gyrification in fetuses and preterm newborns but the question remains as to whether cortical-related measurements derived from both cases are comparable or not. Indeed, the developmental folding trajectories drawn up from both populations have not been compared so far, neither from cross-sectional nor from longitudinal datasets. The present study aimed to compare features of cortical folding between healthy fetuses and early imaged preterm newborns on a cross-sectional basis, over a developmental period critical for the folding process (21-36 weeks of gestational age [GA]). A particular attention was carried out to reduce the methodological biases between the 2 populations. To provide an accurate group comparison, several global parameters characterizing the cortical morphometry were derived. In both groups, those metrics provided good proxies for the dramatic brain growth and cortical folding over this developmental period. Except for the cortical volume and the rate of sulci appearance, they depicted different trajectories in both groups suggesting that the transition from into ex utero has a visible impact on cortical morphology that is at least dependent on the GA at birth in preterm newborns.

  18. François Leroy, Qing Cai, Stephanie L. Bogart, Jessica Dubois, Olivier Coulon, Karla Monzalvo, Clara Fischer, Hervé Glasel, Lise Van der Haegen, Audrey Bénézit, Ching-Po Lin, David N. Kennedy, Aya S. Ihara, Lucie Hertz-Pannier, Marie-Laure Moutard, Cyril Poupon, Marc Brysbaert, Neil Roberts, William D. Hopkins, Jean-François Mangin, and Ghislaine Dehaene-Lambertz. New human-specific brain landmark: the depth asymmetry of superior temporal sulcus.. Proc Natl Acad Sci U S A, 112(4):1208--1213, January 2015. [WWW] [PDF]
    Abstract: Identifying potentially unique features of the human cerebral cortex is a first step to understanding how evolution has shaped the brain in our species. By analyzing MR images obtained from 177 humans and 73 chimpanzees, we observed a human-specific asymmetry in the superior temporal sulcus at the heart of the communication regions and which we have named the "superior temporal asymmetrical pit" (STAP). This 45-mm-long segment ventral to Heschl's gyrus is deeper in the right hemisphere than in the left in 95\110276300f typical human subjects, from infanthood till adulthood, and is present, irrespective of handedness, language lateralization, and sex although it is greater in males than in females. The STAP also is seen in several groups of atypical subjects including persons with situs inversus, autistic spectrum disorder, Turner syndrome, and corpus callosum agenesis. It is explained in part by the larger number of sulcal interruptions in the left than in the right hemisphere. Its early presence in the infants of this study as well as in fetuses and premature infants suggests a strong genetic influence. Because this asymmetry is barely visible in chimpanzees, we recommend the STAP region during midgestation as an important phenotype to investigate asymmetrical variations of gene expression among the primate lineage. This genetic target may provide important insights regarding the evolution of the crucial cognitive abilities sustained by this sulcus in our species, namely communication and social cognition.

  19. Sébastien Marti, Laurie Bayet, and Stanislas Dehaene. Subjective report of eye fixations during serial search.. Conscious Cogn, 33C:1--15, December 2015. [WWW] [PDF]
    Abstract: Humans readily introspect upon their thoughts and their behavior, but how reliable are these subjective reports? In the present study, we explored the consistencies of and differences between the observer's subjective report and actual behavior within a single trial. On each trial of a serial search task, we recorded eye movements and the participants' beliefs of where their eyes moved. The comparison of reported versus real eye movements revealed that subjects successfully reported a subset of their eye movements. Limits in subjective reports stemmed from both the number and the type of eye movements. Furthermore, subjects sometimes reported eye movements they actually never made. A detailed examination of these reports suggests that they could reflect covert shifts of attention during overt serial search. Our data provide quantitative and qualitative measures of observers' subjective reports and reveal experimental effects of visual search that would otherwise be inaccessible.

  20. Sebastien Marti, Jean-Remi King, and Stanislas DEHAENE. Time-Resolved Decoding of Two Processing Chains during Dual-Task Interference. Neuron, 88:1-11, December 16 2015. [PDF] [bibtex-entry]

  21. Olivier Martinaud, Dorothée Pouliquen, Dominique Parain, Alice Goldenberg, Emmanuel Gérardin, Didier Hannequin, Irène Altarelli, Franck Ramus, Lucie Hertz-Pannier, Ghislaine Dehaene-Lambertz, and Laurent Cohen. Impaired functional differentiation for categories of objects in the ventral visual stream: A case of developmental visual impairment.. Neuropsychologia, 77:52--61, August 2015. [WWW] [PDF]
    Abstract: We report the case of a 14-year-old girl suffering from severe developmental visual impairment along with delayed language and cognitive development, and featuring a clear-cut dissociation between spared dorsal and impaired ventral visual pathways. Visual recognition of objects, including faces and printed words, was affected. In contrast, movement perception and visually guided motor control were preserved. Structural MRI was normal on inspection, but Voxel Based Morphometry (VBM) revealed reduced grey matter density in the mesial occipital and ventral occipito-temporal cortex. Functional MRI during the perception of line drawings uncovered impaired differentiation which is normally observed at even younger ages: no local category preferences could be identified within the occipito-temporal cortex for faces, houses, words or tools. In contrast, movement-related activations appeared to be normal. Finally, those abnormalities evolved on the background of chronic bilateral occipital epileptic activity, including continuous spike-wave discharges during sleep, which may be considered as the primary cause of non-specific intellectual disability and visual impairment.

  22. Karima Mersad and Ghislaine Dehaene-Lambertz. Electrophysiological evidence of phonetic normalization across coarticulation in infants.. Dev Sci, August 2015. [WWW] [PDF]
    Abstract: The auditory neural representations of infants can easily be studied with electroencephalography using mismatch experimental designs. We recorded high-density event-related potentials while 3-month-old infants were listening to trials consisting of CV syllables produced with different vowels (/bX/ or /gX/). The consonant remained the same for the first three syllables, followed (or not) by a change in the fourth position. A consonant change evoked a significant difference around the second auditory peak (400-600 ms) relative to control trials. This mismatch response demonstrates that the infants robustly categorized the consonant despite coarticulation that blurs the phonetic cues, and at an age at which they do not produce these consonants themselves. This response was obtained even when infants had no visual articulatory information to help them to track the consonant repetition. In combination with previous studies establishing categorical perception and normalization across speakers, this result demonstrates that preverbal infants already have abstract phonetic representation integrating over acoustical features in the first months of life.

  23. Florent Meyniel, Daniel Schlunegger, and Stanislas Dehaene. The Sense of Confidence during Probabilistic Learning: A Normative Account.. PLoS Comput Biol, 11(6):e1004305, June 2015. [WWW] [PDF]
    Abstract: Learning in a stochastic environment consists of estimating a model from a limited amount of noisy data, and is therefore inherently uncertain. However, many classical models reduce the learning process to the updating of parameter estimates and neglect the fact that learning is also frequently accompanied by a variable "feeling of knowing" or confidence. The characteristics and the origin of these subjective confidence estimates thus remain largely unknown. Here we investigate whether, during learning, humans not only infer a model of their environment, but also derive an accurate sense of confidence from their inferences. In our experiment, humans estimated the transition probabilities between two visual or auditory stimuli in a changing environment, and reported their mean estimate and their confidence in this report. To formalize the link between both kinds of estimate and assess their accuracy in comparison to a normative reference, we derive the optimal inference strategy for our task. Our results indicate that subjects accurately track the likelihood that their inferences are correct. Learning and estimating confidence in what has been learned appear to be two intimately related abilities, suggesting that they arise from a single inference process. We show that human performance matches several properties of the optimal probabilistic inference. In particular, subjective confidence is impacted by environmental uncertainty, both at the first level (uncertainty in stimulus occurrence given the inferred stochastic characteristics) and at the second level (uncertainty due to unexpected changes in these stochastic characteristics). Confidence also increases appropriately with the number of observations within stable periods. Our results support the idea that humans possess a quantitative sense of confidence in their inferences about abstract non-sensory parameters of the environment. This ability cannot be reduced to simple heuristics, it seems instead a core property of the learning process.

  24. Florent Meyniel, Mariano Sigman, and Zachary F. Mainen. Confidence as Bayesian Probability: From Neural Origins to Behavior.. Neuron, 88(1):78--92, October 2015. [WWW] [PDF]
    Abstract: Research on confidence spreads across several sub-fields of psychology and neuroscience. Here, we explore how a definition of confidence as Bayesian probability can unify these viewpoints. This computational view entails that there are distinct forms in which confidence is represented and used in the brain, including distributional confidence, pertaining to neural representations of probability distributions, and summary confidence, pertaining to scalar summaries of those distributions. Summary confidence is, normatively, derived or "read out" from distributional confidence. Neural implementations of readout will trade off optimality versus flexibility of routing across brain systems, allowing confidence to serve diverse cognitive functions.

  25. Clément Moutard, Stanislas Dehaene, and Rafael Malach. Spontaneous Fluctuations and Non-linear Ignitions: Two Dynamic Faces of Cortical Recurrent Loops.. Neuron, 88(1):194--206, October 2015. [WWW] [PDF]
    Abstract: Recent human neurophysiological recordings have uncovered two fundamental modes of cerebral cortex activity with distinct dynamics: an active mode characterized by a rapid and sustained activity ("ignition") and a spontaneous (resting-state) mode, manifesting ultra-slow fluctuations of low amplitude. We propose that both dynamics reflect two faces of the same recurrent loop mechanism: an integration device that accumulates ongoing stochastic activity and, either spontaneously or in a task-driven manner, crosses a dynamic threshold and ignites, leading to content-specific awareness. The hypothesis can explain a rich set of behavioral and neuronal phenomena, such as perceptual threshold, the high non-linearity of visual responses, the subliminal nature of spontaneous activity fluctuations, and the slow activity buildup anticipating spontaneous behavior (e.g., readiness potential). Further elaborations of this unified scheme, such as a cascade of integrators with different ignition thresholds or multi-stable states, can account for additional complexities in the repertoire of human cortical dynamics.

  26. Lionel Naccache, Jean-Rémi King, Jacobo Sitt, Denis Engemann, Imen El Karoui, Benjamin Rohaut, Frédéric Faugeras, Srivas Chennu, Mélanie Strauss, Tristan Bekinschtein, and Stanislas Dehaene. Neural detection of complex sound sequences or of statistical regularities in the absence of consciousness?. Brain, July 2015. [WWW] [PDF] [bibtex-entry]

  27. Moti Salti, Simo Monto, Lucie Charles, Jean-Remi King, Lauri Parkkonen, and Stanislas Dehaene. Distinct cortical codes and temporal dynamics for conscious and unconscious percepts.. Elife, 4, 2015. [WWW]
    Abstract: The neural correlates of consciousness are typically sought by comparing the overall brain responses to perceived and unperceived stimuli. However, this comparison may be contaminated by non-specific attention, alerting, performance, and reporting confounds. Here, we pursue a novel approach, tracking the neuronal coding of consciously and unconsciously perceived contents while keeping behavior identical (blindsight). EEG and MEG were recorded while participants reported the spatial location and visibility of a briefly presented target. Multivariate pattern analysis demonstrated that considerable information about spatial location traverses the cortex on blindsight trials, but that starting ?270 ms post-onset, information unique to consciously perceived stimuli, emerges in superior parietal and superior frontal regions. Conscious access appears characterized by the entry of the perceived stimulus into a series of additional brain processes, each restricted in time, while the failure of conscious access results in the breaking of this chain and a subsequent slow decay of the lingering unconscious activity.

  28. Aaron Schurger, Min-Soo Kim, and Jonathan D. Cohen. Paradoxical Interaction between Ocular Activity, Perception, and Decision Confidence at the Threshold of Vision.. PLoS One, 10(5):e0125278, 2015. [WWW]
    Abstract: In humans and some other species perceptual decision-making is complemented by the ability to make confidence judgements about the certainty of sensory evidence. While both forms of decision process have been studied empirically, the precise relationship between them remains poorly understood. We performed an experiment that combined a perceptual decision-making task (identifying the category of a faint visual stimulus) with a confidence-judgement task (wagering on the accuracy of each perceptual decision). The visual stimulation paradigm required steady fixation, so we used eye-tracking to control for stray eye movements. Our data analyses revealed an unexpected and counterintuitive interaction between the steadiness of fixation (prior to and during stimulation), perceptual decision making, and post-decision wagering: greater variability in gaze direction during fixation was associated with significantly increased visual-perceptual sensitivity, but significantly decreased reliability of confidence judgements. The latter effect could not be explained by a simple change in overall confidence (i.e. a criterion artifact), but rather was tied to a change in the degree to which high wagers predicted correct decisions (i.e. the sensitivity of the confidence judgement). We found no evidence of a differential change in pupil diameter that could account for the effect and thus our results are consistent with fixational eye movements being the relevant covariate. However, we note that small changes in pupil diameter can sometimes cause artefactual fluctuations in measured gaze direction and this possibility could not be fully ruled out. In either case, our results suggest that perceptual decisions and confidence judgements can be processed independently and point toward a new avenue of research into the relationship between them.

  29. Aaron Schurger, Ioannis Sarigiannidis, Lionel Naccache, Jacobo D. Sitt, and Stanislas Dehaene. Cortical activity is more stable when sensory stimuli are consciously perceived.. Proc Natl Acad Sci U S A, 112(16):E2083--E2092, April 2015. [WWW]
    Abstract: According to recent evidence, stimulus-tuned neurons in the cerebral cortex exhibit reduced variability in firing rate across trials, after the onset of a stimulus. However, in order for a reduction in variability to be directly relevant to perception and behavior, it must be realized within trial--the pattern of activity must be relatively stable. Stability is characteristic of decision states in recurrent attractor networks, and its possible relevance to conscious perception has been suggested by theorists. However, it is difficult to measure on the within-trial time scales and broadly distributed spatial scales relevant to perception. We recorded simultaneous magneto- and electroencephalography (MEG and EEG) data while subjects observed threshold-level visual stimuli. Pattern-similarity analyses applied to the data from MEG gradiometers uncovered a pronounced decrease in variability across trials after stimulus onset, consistent with previous single-unit data. This was followed by a significant divergence in variability depending upon subjective report (seen/unseen), with seen trials exhibiting less variability. Applying the same analysis across time, within trial, we found that the latter effect coincided in time with a difference in the stability of the pattern of activity. Stability alone could be used to classify data from individual trials as "seen" or "unseen." The same metric applied to EEG data from patients with disorders of consciousness exposed to auditory stimuli diverged parametrically according to clinically diagnosed level of consciousness. Differences in signal strength could not account for these results. Conscious perception may involve the transient stabilization of distributed cortical networks, corresponding to a global brain-scale decision.

  30. Aaron Schurger and Sebo Uithol. Nowhere and Everywhere: The Causal Origin of Voluntary Action. Review of Philosophy and Psychology, 19 March, 2015. [WWW] [bibtex-entry]

  31. Melanie Strauss, Jacobo D. Sitt, Jean-Remi King, Maxime Elbaz, Leila Azizi, Marco Buiatti, Lionel Naccache, Virginie van Wassenhove, and Stanislas Dehaene. Disruption of hierarchical predictive coding during sleep. Proc Natl Acad Sci U S A, March 2015. [WWW] [PDF]
    Abstract: When presented with an auditory sequence, the brain acts as a predictive-coding device that extracts regularities in the transition probabilities between sounds and detects unexpected deviations from these regularities. Does such prediction require conscious vigilance, or does it continue to unfold automatically in the sleeping brain? The mismatch negativity and P300 components of the auditory event-related potential, reflecting two steps of auditory novelty detection, have been inconsistently observed in the various sleep stages. To clarify whether these steps remain during sleep, we recorded simultaneous electroencephalographic and magnetoencephalographic signals during wakefulness and during sleep in normal subjects listening to a hierarchical auditory paradigm including short-term (local) and long-term (global) regularities. The global response, reflected in the P300, vanished during sleep, in line with the hypothesis that it is a correlate of high-level conscious error detection. The local mismatch response remained across all sleep stages (N1, N2, and REM sleep), but with an incomplete structure; compared with wakefulness, a specific peak reflecting prediction error vanished during sleep. Those results indicate that sleep leaves initial auditory processing and passive sensory response adaptation intact, but specifically disrupts both short-term and long-term auditory predictive coding.

  32. Liping Wang, Lynn Uhrig, Bechir Jarraya, and Stanislas Dehaene. Representation of Numerical and Sequential Patterns in Macaque and Human Brains. Current Biology, 2015. [PDF] [bibtex-entry]



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