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Visual Hull-Based Geometric Data Compression of a 3-D Object

IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY 2015年第7期25卷 1151-1160页

作者： Hwang, Sung Soo Kim, Wook-Joong Yoo, Jisung Kim, Seong Dae Korea Adv Inst Sci & Technol Dept Elect Engn Taejon 305701 South Korea Eastern Kentucky Univ Richmond KY 40475 USA

As image-based 3-D modeling is used in a variety of applications, accordingly, the compression of 3-D object geometry represented by multiple images becomes an important task. This paper presents a model-based approach to predict the geometric structure of an object using its visual hull. A visual hull is a geometric entity generated by shape-from-silhouette (SFS), and consequently it largely follows the overall shape of the object. The construction of a visual hull is computationally inexpensive and a visual hull can be encoded with relatively small amount of bits because it can be represented with 2-D silhouette images. Therefore, when it comes to the predictive compression of object's geometric data, the visual hull should be an effective predictor. In the proposed method, the geometric structure of an object is represented by a layered depth image (LDI), and a visual hull from the LDI data is computed via silhouette generation and SFS. The geometry of an object is predicted with the computed visual hull, and the visual hull data with its prediction errors are encoded. Simulation results show that the proposed predictive coding based on visual hull outperforms the previous image-based methods and the partial surface-based method.

关键词： 3-D object coding layered depth image (LDI) predictive coding shape-from-silhouette (SFS) visual hull

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Network Activity Underlying the Illusory Self-Attribution of a Dummy Arm

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HUMAN BRAIN MAPPING 2015年第6期36卷 2284-2304页

作者： Limanowski, Jakub Blankenburg, Felix Free Univ Berlin Neurocomputat & Neuroimaging Unit Dept Educ & Psychol D-14195 Berlin Germany Humboldt Univ Berlin Sch Mind & Brain D-10099 Berlin Germany

Neuroimaging has demonstrated that the illusory self-attribution of body parts engages frontal and intraparietal brain areas, and recent evidence further suggests an involvement of visual body-selective regions in the occipitotemporal cortex. However, little is known about the principles of information exchange within this network. Here, using automated congruent versus incongruent visuotactile stimulation of distinct anatomical locations on the participant's right arm and a realistic dummy counterpart in an fMRI scanner, we induced an illusory self-attribution of the dummy arm. The illusion consistently activated a left-hemispheric network comprising ventral premotor cortex (PMv), intraparietal sulcus (IPS), and body-selective regions of the lateral occipitotemporal cortex (LOC). Importantly, during the illusion, the functional coupling of the PMv and the IPS with the LOC increased substantially, and dynamic causal modeling revealed a significant enhancement of connections from the LOC and the secondary somatosensory cortex to the IPS. These results comply with the idea that the brain's inference mechanisms rely on the hierarchical propagation of prediction error. During illusory self-attribution, unpredicted ambiguous sensory input about one's body configuration may result in the generation of such prediction errors in visual and somatosensory areas, which may be conveyed to parietal integrative areas. Hum Brain Mapp 36:2284-2304, 2015. (c) 2015 Wiley Periodicals, Inc.

关键词： extrastriate body area body ownership intraparietal sulcus peripersonal space predictive coding rubber hand illusion self-attribution

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Symbol coding of Laplacian distributed prediction residuals

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DIGITAL SIGNAL PROCESSING 2015年第1期44卷 76-87页

作者： Ali, Mortuza Murshed, Manzur Federat Univ Australia Sch Engn & IT Churchill Vic 3842 Australia

predictive coding schemes, proposed in the literature, essentially model the residuals with discrete distributions. However, real-valued residuals can arise in predictive coding, for example, from the usage of an r order linear predictor specified by r real-valued coefficients. In this paper, we propose a symbol-by-symbol coding scheme for the Laplace distribution, which closely models the distribution of real-valued residuals in practice. To efficiently exploit the real-valued predictions at a given precision, the proposed scheme essentially combines the process of residual computation and coding, in contrast to conventional schemes that separate these two processes. In the context of adaptive predictive coding framework, where the source statistics must be learnt from the data, the proposed scheme has the advantage of lower 'model cost' as it involves learning only one parameter. In this paper, we also analyze the proposed parametric coding scheme to establish the relationship between the optimal value of the coding parameter and the scale parameter of the Laplace distribution. Our experimental results demonstrated the compression efficiency and computational simplicity of the proposed scheme in adaptive coding of residuals against the widely used arithmetic coding, Rice-Golomb coding, and the Merhav-Seroussi-Weinberger scheme adopted in JPEG-LS. (C) 2015 Elsevier Inc. All rights reserved.

关键词： predictive coding Symbol-by-symbol coding Laplace distribution Golomb code Rice mapping

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Prediction and constraint in audiovisual speech perception

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CORTEX 2015年 68卷 169-181页

作者： Peelle, Jonathan E. Sommers, Mitchell S. Washington Univ Dept Otolaryngol St Louis MO 63110 USA Washington Univ Dept Psychol St Louis MO 63130 USA

During face-to-face conversational speech listeners must efficiently process a rapid and complex stream of multisensory information. Visual speech can serve as a critical complement to auditory information because it provides cues to both the timing of the incoming acoustic signal (the amplitude envelope, influencing attention and perceptual sensitivity) and its content (place and manner of articulation, constraining lexical selection). Here we review behavioral and neurophysiological evidence regarding listeners' use of visual speech information. Multisensory integration of audiovisual speech cues improves recognition accuracy, particularly for speech in noise. Even when speech is intelligible based solely on auditory information, adding visual information may reduce the cognitive demands placed on listeners through increasing the precision of prediction. Electrophysiological studies demonstrate that oscillatory cortical entrainment to speech in auditory cortex is enhanced when visual speech is present, increasing sensitivity to important acoustic cues. Neuroimaging studies also suggest increased activity in auditory cortex when congruent visual information is available, but additionally emphasize the involvement of heteromodal regions of posterior superior temporal sulcus as playing a role in integrative processing. We interpret these findings in a framework of temporally-focused lexical competition in which visual speech information affects auditory processing to increase sensitivity to acoustic information through an early integration mechanism, and a late integration stage that incorporates specific information about a speaker's articulators to constrain the number of possible candidates in a spoken utterance. Ultimately it is words compatible with both auditory and visual information that most strongly determine successful speech perception during everyday listening. Thus, audiovisual speech perception is accomplished through multiple stages of integration, su

关键词： Speech perception Audiovisual speech Multisensory integration predictive coding predictive timing

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Onboard Image Processing System for Hyperspectral Sensor

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SENSORS 2015年第10期15卷 24926-24944页

作者： Hihara, Hiroki Moritani, Kotaro Inoue, Masao Hoshi, Yoshihiro Iwasaki, Akira Takada, Jun Inada, Hitomi Suzuki, Makoto Seki, Taeko Ichikawa, Satoshi Tanii, Jun NEC Space Technol Ltd Fuchu Tokyo 1838551 Japan Univ Tokyo Res Ctr Adv Sci & Technol Meguro Ku Tokyo 1538904 Japan NEC Corp Ltd Cent Res Lab Nakahara Ku Kawasaki Kanagawa 2118666 Japan NEC Corp Ltd Div Space Syst Fuchu Tokyo 1838551 Japan Japan Aerosp Explorat Agcy JAXA Inst Space Astronaut Sci Chuo Ku Sagamihara Kanagawa 2525210 Japan Japan Aerosp Explorat Agcy JAXA Aerosp Res & Dev Directorate Tsukuba Ibaraki 3058505 Japan Japan Space Syst Minato Ku Tokyo 1050011 Japan

Onboard image processing systems for a hyperspectral sensor have been developed in order to maximize image data transmission efficiency for large volume and high speed data downlink capacity. Since more than 100 channels are required for hyperspectral sensors on Earth observation satellites, fast and small-footprint lossless image compression capability is essential for reducing the size and weight of a sensor system. A fast lossless image compression algorithm has been developed, and is implemented in the onboard correction circuitry of sensitivity and linearity of Complementary Metal Oxide Semiconductor (CMOS) sensors in order to maximize the compression ratio. The employed image compression method is based on Fast, Efficient, Lossless Image compression System (FELICS), which is a hierarchical predictive coding method with resolution scaling. To improve FELICS's performance of image decorrelation and entropy coding, we apply a two-dimensional interpolation prediction and adaptive Golomb-Rice coding. It supports progressive decompression using resolution scaling while still maintaining superior performance measured as speed and complexity. coding efficiency and compression speed enlarge the effective capacity of signal transmission channels, which lead to reducing onboard hardware by multiplexing sensor signals into a reduced number of compression circuits. The circuitry is embedded into the data formatter of the sensor system without adding size, weight, power consumption, and fabrication cost.

关键词： hyperspectral sensor Golomb-Rice coding hierarchical prediction lossless image compression predictive coding resolution scaling onboard correction smile correction

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Attentional Enhancement of Auditory Mismatch Responses: a DCM/MEG Study

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CEREBRAL CORTEX 2015年第11期25卷 4273-4283页

作者： Auksztulewicz, Ryszard Friston, Karl UCL Inst Neurol Wellcome Trust Ctr Neuroimaging London WC1N 3BG England

Despite similar behavioral effects, attention and expectation influence evoked responses differently: Attention typically enhances event-related responses, whereas expectation reduces them. This dissociation has been reconciled under predictive coding, where prediction errors are weighted by precision associated with attentional modulation. Here, we tested the predictive coding account of attention and expectation using magnetoencephalography and modeling. Temporal attention and sensory expectation were orthogonally manipulated in an auditory mismatch paradigm, revealing opposing effects on evoked response amplitude. Mismatch negativity (MMN) was enhanced by attention, speaking against its supposedly pre-attentive nature. This interaction effect was modeled in a canonical microcircuit using dynamic causal modeling, comparing models with modulation of extrinsic and intrinsic connectivity at different levels of the auditory hierarchy. While MMN was explained by recursive interplay of sensory predictions and prediction errors, attention was linked to the gain of inhibitory interneurons, consistent with its modulation of sensory precision.

关键词： attention dynamic causal modeling expectation magnetoencephalography predictive coding

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Unfamiliar Walking Movements Are Detected Early in the Visual Stream: An fMRI Study

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CEREBRAL CORTEX 2015年第8期25卷 2022-2034页

作者： Maffei, Vincenzo Giusti, Maria Assunta Macaluso, Emiliano Lacquaniti, Francesco Viviani, Paolo IRCCS Santa Lucia Fdn Lab Neuromotor Physiol I-00179 Rome Italy IRCCS Santa Lucia Fdn Lab Neuroimaging I-00179 Rome Italy Univ Roma Tor Vergata Ctr Space BioMed I-00133 Rome Italy Univ Roma Tor Vergata Dept Syst Med I-00133 Rome Italy

Two experiments investigated the network involved in the visual perception of walking. Video clips of forward and backward walk (real walk direction) were shown either as recorded, or reversed in time (rendering). In Experiment 1 (identification task), participants were asked to indicate whether or not the stimulus was time-reversed. In Experiment 2 (free-viewing), participants viewed the video clips passively. Identification accuracy was good with the more familiar scene, that is, when the visual walk was in the direction of the facing orientation, and at chance level in the opposite case. In both experiments, the temporo-occipital junction (TOJ) was activated more strongly by unfamiliar than familiar scenes. Only in Experiment 1 intraparietal, superior temporal, and inferior temporal regions were also activated. TOJ activation signals the detection in unfamiliar scenes of a mismatch between facing orientation and visual movement direction. We argue that TOJ response to a mismatch prevents the further processing of the visual input required to identify temporal inversions. When no mismatch is detected (familiar stimuli), TOJ would, instead, be involved in the kinematic analysis that makes such identification possible. The study demonstrates that unfamiliar walking movements are detected earlier than so far assumed along the visual movement processing stream.

关键词： action observation biological motion fMRI predictive coding

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Duration estimation entails predicting when

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NEUROIMAGE 2015年 106卷 272-283页

作者： van Wassenhove, Virginie Lecoutre, Lucille CEA DSV I2BM NeuroSpin INSERMU992Cognit Neuroimaging Unit F-91191 Gif Sur Yvette France

The estimation of duration can be affected by context and surprise. Using MagnetoEncephaloGraphy (MEG), we tested whether increased neural activity during surprise and following neural suppression in two different contexts supported subjective time dilation (Eagleman and Pariyadath, 2009;Pariyadath and Eagleman, 2012). Sequences of three 300 ms frequency-modulated (FM, control) or pure tones (test) were presented and followed by a fourth FM varying in duration. In test, the last FM was perceived as significantly longer than veridical duration (Tse et al., 2004) but did not differ from the perceived duration in control. Several novel and distinct neural signatures were observed in duration estimation: first, neural suppression of standard stimuli was observed for the onset but not for the offset auditory evoked responses. Second, ramping activity increased with veridical duration in control where as at the same latency in test, the amplitude of the midlatency response increased with the distance of deviant durations. Third, in both conditions, the amplitude of the offset auditory evoked responses accounted well for participants' performance: the longer the perceived duration, the larger the offset response. Fourth, neural duration demarcated by the peak latencies of the onset and ramping evoked activities indexed a systematic time compression that reliably predicted subjective time perception. Our findings suggest that interval timing undergoes time compression by capitalizing on the predicted offset of an auditory event. (C) 2014 Elsevier Inc. All rights reserved.

关键词： MMN predictive coding Ramping activity Midlatency response Interval timing

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Prediction across sensory modalities: A neurocomputational model of the McGurk effect

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CORTEX 2015年 68卷 61-75页

作者： Olasagasti, Itsaso Bouton, Sophie Giraud, Anne-Lise Univ Geneva Dept Basic Neurosci CH-1211 Geneva 4 Switzerland

The McGurk effect is a textbook illustration of the automaticity with which the human brain integrates audio-visual speech. It shows that even incongruent audiovisual (AV) speech stimuli can be combined into percepts that correspond neither to the auditory nor to the visual input, but to a mix of both. Typically, when presented with, e.g., visual/aga/ and acoustic /aba/ we perceive an illusory /ada/. In the inverse situation, however, when acoustic /aga/ is paired with visual labs!, we perceive a combination of both stimuli, i.e., /abga/ or /agba/. Here we assessed the role of dynamic cross-modal predictions in the outcome of AV speech integration using a computational model that processes continuous audiovisual speech sensory inputs in a predictive coding framework. The model involves three processing levels: sensory units, units that encode the dynamics of stimuli, and multimodal recognition/identity units. The model exhibits a dynamic prediction behavior because evidence about speech tokens can be asynchronous across sensory modality, allowing for updating the activity of the recognition units from one modality while sending top down predictions to the other modality. We explored the model's response to congruent and incongruent AV stimuli and found that, in the two-dimensional feature space spanned by the speech second formant and lip aperture, fusion stimuli are located in the neighborhood of congruent /ada/, which therefore provides a valid match. Conversely, stimuli that lead to combination percepts do not have a unique valid neighbor. In that case, acoustic and visual cues are both highly salient and generate conflicting predictions in the other modality that cannot be fused, forcing the elaboration of a combinatorial solution. We propose that dynamic predictive mechanisms play a decisive role in the dichotomous perception of incongruent audiovisual inputs. (C) 2015 Published by Elsevier Ltd.

关键词： predictive coding Audiovisual integration Computational modeling McGurk effect

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Elementary sensory deficits in schizophrenia indexed by impaired visual mismatch negativity

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SCHIZOPHRENIA RESEARCH 2015年第1-3期166卷 164-170页

作者： Farkas, Kinga Stefanics, Gabor Marosi, Csilla Csukly, Gabor Semmelweis Univ Dept Psychiat & Psychotherapy H-1083 Budapest Hungary Univ Zurich Inst Biomed Engn TNU CH-8092 Zurich Switzerland ETH CH-8092 Zurich Switzerland Univ Zurich Dept Econ Lab Social & Neural Syst Res CH-8091 Zurich Switzerland

Introduction: Mismatch negativity (MMN) is an automatic brain response to unexpected events. It represents a prediction error (PE) response, reflecting the difference between the sensory input and predictions. While deficits in auditory MMN are well known in schizophrenia, only few studies investigated impairments in predictive visual processing in schizophrenia. These studies used complex stimuli such as motion direction and emotional facial expressions. Here we studied whether automatic predictive processing of elementary features such as orientation is also impaired in schizophrenia. Methods: Altogether 28 patients with schizophrenia and 27 healthy controls matched in age, gender, and education participated in the study. EEG was recorded using 128 channels in the two experimental blocks. Using an oddball paradigm, horizontal stripes of Gabor patches were presented as frequent standards and vertical stripes as rare deviants in one block. Stimulus probabilities were swapped in the other block. Mismatch responses were obtained by subtracting responses to standard from those to deviant stimuli. Results: We found significant mismatch responses in healthy controls but not in patients in the prefrontal and occipital-parietal regions in the 90-200 ms interval. Furthermore patients showed significantly decreased deviant minus standard difference waveforms relative to controls in the same regions with moderate to large effect sizes. Conclusions: Our findings demonstrate that predictive processing of unattended low-level visual features such as orientation is impaired in schizophrenia. Our results complement reports of sensory deficits found in tasks requiring attentive processing and suggest that deficits are present in automaticvisual sensory processes putatively mediated by glutamatergic functioning. (C) 2015 Published by Elsevier B.V.

关键词： ERP Perceptual prediction error predictive coding Visual mismatch negativity Schizophrenia EEG MMN

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