129 research outputs found
Parametric study of EEG sensitivity to phase noise during face processing
Get PDF<b>Background: </b>
The present paper examines the visual processing speed of complex objects, here faces, by mapping the relationship between object physical properties and single-trial brain responses. Measuring visual processing speed is challenging because uncontrolled physical differences that co-vary with object categories might affect brain measurements, thus biasing our speed estimates. Recently, we demonstrated that early event-related potential (ERP) differences between faces and objects are preserved even when images differ only in phase information, and amplitude spectra are equated across image categories. Here, we use a parametric design to study how early ERP to faces are shaped by phase information. Subjects performed a two-alternative force choice discrimination between two faces (Experiment 1) or textures (two control experiments). All stimuli had the same amplitude spectrum and were presented at 11 phase noise levels, varying from 0% to 100% in 10% increments, using a linear phase interpolation technique. Single-trial ERP data from each subject were analysed using a multiple linear regression model.
<b>Results: </b>
Our results show that sensitivity to phase noise in faces emerges progressively in a short time window between the P1 and the N170 ERP visual components. The sensitivity to phase noise starts at about 120–130 ms after stimulus onset and continues for another 25–40 ms. This result was robust both within and across subjects. A control experiment using pink noise textures, which had the same second-order statistics as the faces used in Experiment 1, demonstrated that the sensitivity to phase noise observed for faces cannot be explained by the presence of global image structure alone. A second control experiment used wavelet textures that were matched to the face stimuli in terms of second- and higher-order image statistics. Results from this experiment suggest that higher-order statistics of faces are necessary but not sufficient to obtain the sensitivity to phase noise function observed in response to faces.
<b>Conclusion: </b>
Our results constitute the first quantitative assessment of the time course of phase information processing by the human visual brain. We interpret our results in a framework that focuses on image statistics and single-trial analyses
Adaptation of Learning and Operation Methods to Specific Needs of Future Networks and Services (Deliverable 3.7, Univerself)
No full textProject DeliverableInternational audienceThis deliverable describes the adaptation of learning and operation methods to specific needs of future networks and services in the context of the Univerself project. Full list of authors per institution: UniS: Stylianos Georgoulas, Majid Ghader, ALBLI: Rouzbeh Razavi, INRIA : Rémi Badonnel, Martin Barrere, Olivier Festor, FT: Zwi Altman, Richard Combes, TID: Beatriz Fuentes, Carolina García-Vázquez, UPRC: Kostas Tsagkaris, Panagiotis Demestichas, Vera Stavroulaki, Panagiotis Vlacheas, Yiouli Kritikou, Nikos Koutsouris, Aimilia Bantouna, Dimitris Karvounas, Evagelia Tzifa, Assimina Sarli, Marios Logothetis, Andreas Georgakopoulos, Louiza Papadopoulou, Vassilis Foteinos, Dimitris Kelaidonis, George Poulios, NEC: Johannes Lessmann, Zarrar Yousaf, Telecom Italia: Antonio Manzalini, Giorgio Calochira, UT: Ramin Sadre, Anna Sperotto, ALBLF: Leila Bennacer, Laurent Ciavagli
Adaptation of Learning and Operation Methods to Specific Needs of Future Networks and Services (Deliverable 3.7, Univerself)
No full textProject DeliverableInternational audienceThis deliverable describes the adaptation of learning and operation methods to specific needs of future networks and services in the context of the Univerself project. Full list of authors per institution: UniS: Stylianos Georgoulas, Majid Ghader, ALBLI: Rouzbeh Razavi, INRIA : Rémi Badonnel, Martin Barrere, Olivier Festor, FT: Zwi Altman, Richard Combes, TID: Beatriz Fuentes, Carolina García-Vázquez, UPRC: Kostas Tsagkaris, Panagiotis Demestichas, Vera Stavroulaki, Panagiotis Vlacheas, Yiouli Kritikou, Nikos Koutsouris, Aimilia Bantouna, Dimitris Karvounas, Evagelia Tzifa, Assimina Sarli, Marios Logothetis, Andreas Georgakopoulos, Louiza Papadopoulou, Vassilis Foteinos, Dimitris Kelaidonis, George Poulios, NEC: Johannes Lessmann, Zarrar Yousaf, Telecom Italia: Antonio Manzalini, Giorgio Calochira, UT: Ramin Sadre, Anna Sperotto, ALBLF: Leila Bennacer, Laurent Ciavagli
The interoperability challenge for autonomic computing
No full textInteroperability is an emerging need for autonomic computing systems, which stems from the very success of these systems. Autonomic computing is increasingly popular; soon autonomic control components will be commonplace, and present in almost every large or complex application. This inevitably leads to situations where multiple autonomic components coexist and interact either directly or indirectly within the same application or system. Problems can arise when numerous independently designed autonomic components interact. We advocate a service-based approach to interoperability and present a set of requirements for such an approach. We briefly present a universal interoperability service which automatically discovers and manages potential conflicts between manager components
Mechanisms of top-down facilitation in perception of visual objects studied by fMRI
Get PDFPrior knowledge regarding the possible identity of an object facilitates its recognition from a degraded visual input, though the underlying mechanisms are unclear. Previous work implicated ventral visual cortex but did not disambiguate whether activity-changes in these regions are causal to or merely reflect an effect of facilitated recognition. We used functional magnetic resonance imaging to study top-down influences on processing of gradually revealed objects, by preceding each object with a name that was congruent or incongruent with the object. Congruently primed objects were recognized earlier than incongruently primed, and this was paralleled by shifts in activation profiles for ventral visual, parietal, and prefrontal cortices. Prior to recognition, defined on a trial-by-trial basis, activity in ventral visual cortex rose gradually but equivalently for congruently and incongruently primed objects. In contrast, prerecognition activity was greater with congruent priming in lateral parietal, retrosplenial, and lateral prefrontal cortices, whereas functional coupling between parietal and ventral visual (and also left lateral prefrontal and parietal) cortices was enhanced in the same context. Thus, when controlling for recognition point and stimulus information, activity in ventral visual cortex mirrors recognition success, independent of condition. Facilitation by top-down cues involves lateral parietal cortex interacting with ventral visual areas, potentially explaining why parietal lesions can lead to deficits in recognizing degraded objects even in the context of top-down knowledge
The development of a simple process for producing medicinal diagnostic 18F agents for molecular imaging using positron-emission-tomography
No full textA range of resin bound sulfonate ester linkers were developed for use in the resin-linker-vector (RLV) approach for the synthesis of [18F]-fluoride radiotracers for use as imaging agents in positron-emission-tomography (PET). The RLV strategy immobilises a precursor to the desired radiotracer on a solid support which is cleaved on exposure to [18F]-fluoride ion to give the 18F-labelled radiotracer in solution. The RLV methodology allows for easier purification of the 18F-labelled radiotracer as a simple filtration step removes the unreacted starting material and the cleaved resin.Synthetic routes to a 4-allkylphenylsulfonate linker and a 4-nitrophenylsulfonate linker were developed and these were shown to work as desired as part of the RLV construct in [19F]-fluoridolysis reactions. [18F]-Fluoridolysis reactions using the 4-alkylphenylsulfonate linker gave the desired 18F-labelled product in excellent radiochemical purity. The RLV strategy with this linker type was applied in a new synthetic route to O-(2-[18F]-fluoroethyl)-L-tyrosine.A fluorinated analogue of Alzheimer’s disease drug (?)-galanthamine was synthesised with complete stereocontrol as a potential new imaging agent for use in PET
Visual modulation of neurons in auditory cortex
No full textOur brain integrates the information provided by the different sensory modalities into a coherent percept, and recent studies suggest that this process is not restricted to higher association areas. Here we evaluate the hypothesis that auditory cortical fields are involved in cross-modal processing by probing individual neurons for audiovisual interactions. We find that visual stimuli modulate auditory processing both at the level of field potentials and single-unit activity and already in primary and secondary auditory fields. These interactions strongly depend on a stimulus' efficacy in driving the neurons but occur independently of stimulus category and for naturalistic as well as artificial stimuli. In addition, interactions are sensitive to the relative timing of audiovisual stimuli and are strongest when visual stimuli lead by 20-80 msec. Exploring the underlying mechanisms, we find that enhancement correlates with the resetting of slow (∼10 Hz) oscillations to a phase angle of optimal excitability. These results demonstrate that visual stimuli can modulate the firing of neurons in auditory cortex in a manner that depends on stimulus efficacy and timing. These neurons thus meet the criteria for sensory integration and provide the auditory modality with multisensory contextual information about co-occurring environmental events. © The Author 2008. Published by Oxford University Press. All rights reserved
Neural basis for priming of pop-out during visual search revealed with fMRI
No full textMalikovic and Nakayama first showed that visual search efficiency can be influenced by priming effects. Even "pop-out" targets (defined by unique color) are judged quicker if they appear at the same location and/or in the same color as on the preceding trial, in an unpredictable sequence. Here, we studied the potential neural correlates of such priming in human visual search using functional magnetic resonance imaging (fMRI). We found that repeating either the location or the color of a singleton target led to repetition suppression of blood oxygen level-dependent (BOLD) activity in brain regions traditionally linked with attentional control, including bilateral intraparietal sulci. This indicates that the attention system of the human brain can be "primed," in apparent analogy to repetition-suppression effects on activity in other neural systems. For repetition of target color but not location, we also found repetition suppression in inferior temporal areas that may be associated with color processing, whereas repetition of target location led to greater reduction of activation in contralateral inferior parietal and frontal areas, relative to color repetition. The frontal eye fields were also implicated, notably when both target properties (color and location) were repeated together, which also led to further BOLD decreases in anterior fusiform cortex not seen when either property was repeated alone. These findings reveal the neural correlates for priming of pop-out search, including commonalities, differences, and interactions between location and color repetition. fMRI repetition-suppression effects may arise in components of the attention network because these settle into a stable 1. attractor state" more readily when the same target property is repeated than when a different attentional state is required
Causal relationships between frequency bands of extracellular signals in visual cortex revealed by an information theoretic analysis
Get PDFCharacterizing how different cortical rhythms interact and how their interaction changes with sensory stimulation is important to gather insights into how these rhythms are generated and what sensory function they may play. Concepts from information theory, such as Transfer Entropy (TE), offer principled ways to quantify the amount of causation between different frequency bands of the signal recorded from extracellular electrodes; yet these techniques are hard to apply to real data. To address the above issues, in this study we develop a method to compute fast and reliably the amount of TE from experimental time series of extracellular potentials. The method consisted in adapting efficiently the calculation of TE to analog signals and in providing appropriate sampling bias corrections. We then used this method to quantify the strength and significance of causal interaction between frequency bands of field potentials and spikes recorded from primary visual cortex of anaesthetized macaques, both during spontaneous activity and during binocular presentation of naturalistic color movies. Causal interactions between different frequency bands were prominent when considering the signals at a fine (ms) temporal resolution, and happened with a very short (ms-scale) delay. The interactions were much less prominent and significant at coarser temporal resolutions. At high temporal resolution, we found strong bidirectional causal interactions between gamma-band (40-100 Hz) and slower field potentials when considering signals recorded within a distance of 2 mm. The interactions involving gamma bands signals were stronger during movie presentation than in absence of stimuli, suggesting a strong role of the gamma cycle in processing naturalistic stimuli. Moreover, the phase of gamma oscillations was playing a stronger role than their amplitude in increasing causations with slower field potentials and spikes during stimulation. The dominant direction of causality was mainly found in the direction from MUA or gamma frequency band signals to lower frequency signals, suggesting that hierarchical correlations between lower and higher frequency cortical rhythms are originated by the faster rhythms. © The Author(s) 2010
EEG phase patterns reflect the selectivity of neural firing
No full textOscillations are pervasive in encephalographic signals and supposedly reflect cognitive processes and sensory representations. While the relation between oscillation amplitude (power) and sensory-cognitive variables has been extensively studied, recent work reveals that the dynamic oscillation signature (phase pattern) can carry information about such processes to a greater degree than amplitude. To elucidate the neural correlates of oscillatory phase patterns, we compared the stimulus selectivity of neural firing rates and auditory-driven electroencephalogram (EEG) oscillations. We employed the same naturalistic sound stimuli in 2 experiments, one recording scalp EEGs in humans and one recording intracortical local field potentials (LFPs) and single neurons in macaque auditory cortex. Using stimulus decoding techniques, we show that stimulus selective firing patterns imprint on the phase rather than the amplitude of slow (theta band) oscillations in LFPs and EEG. In particular, we find that stimuli which can be discriminated by firing rates can also be discriminated by phase patterns but not by oscillation amplitude and that stimulus-specific phase patterns also persist in the absence of increases of oscillation power. These findings support a neural basis for stimulus selective and entrained EEG phase patterns and reveal a level of interrelation between encephalographic signals and neural firing beyond simple amplitude covariations in both signals. © The Author 2012. Published by Oxford University Press. All rights reserved
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