Perception and perceptual decision-making are strongly facilitated by prior knowledge about the probabilistic structure of the world. While the computational benefits of using prior expectation in perception are clear...
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Perception and perceptual decision-making are strongly facilitated by prior knowledge about the probabilistic structure of the world. While the computational benefits of using prior expectation in perception are clear, there are myriad ways in which this computation can be realized. We review here recent advances in our understanding of the neural sources and targets of expectations in perception. Furthermore, we discuss Bayesian theories of perception that prescribe how an agent should integrate prior knowledge and sensory information, and investigate how current and future empirical data can inform and constrain computational frameworks that implement such probabilistic integration in perception.
Neural oscillations subserve a broad range of functions in speech processing and language comprehension. On the one hand, speech containssomewhatrepetitive trains of air pressure bursts that occur at three dominant am...
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Neural oscillations subserve a broad range of functions in speech processing and language comprehension. On the one hand, speech containssomewhatrepetitive trains of air pressure bursts that occur at three dominant amplitude modulation frequencies, physically marking the linguistically meaningful progressions of phonemes, syllables and intonational phrase boundaries. To these acoustic events, neural oscillations of isomorphous operating frequencies are thought to synchronise, presumably resulting in an implicit temporal alignment of periods of neural excitability to linguistically meaningful spectral information on the three low-level linguistic description levels. On the other hand, speech is a carrier signal that codes for high-level linguistic meaning, such as syntactic structure and semantic informationwhich cannot be read from stimulus acoustics, but must be acquired during language acquisition and decoded for language comprehension. Neural oscillations subserve the processing of both syntactic structure and semantic information. Here, I synthesise a mapping from each linguistic processing domain to a unique set of subserving oscillatory mechanismsthe mapping is plausible given the role ascribed to different oscillatory mechanisms in different subfunctions of cortical information processing and faithful to the underlying electrophysiology. In sum, the present article provides an accessible and extensive review of the functional mechanisms that neural oscillations subserve in speech processing and language comprehension.
Repeatedly searching through invariant spatial arrangements in visual search displays leads to the buildup of memory about these displays (contextual-cueing effect). In the present study, we investigate (1) whether co...
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Repeatedly searching through invariant spatial arrangements in visual search displays leads to the buildup of memory about these displays (contextual-cueing effect). In the present study, we investigate (1) whether contextual cueing is influenced by global statistical properties of the task and, if so, (2) whether these properties increase the overall strength (asymptotic level) or the temporal development (speed) of learning. Experiment 1a served as baseline against which we tested the effects of increased or decreased proportions of repeated relative to nonrepeated displays (Experiments 1b and 1c, respectively), thus manipulating the global statistical properties of search environments. Importantly, probability variations were achieved by manipulating the number of nonrepeated (baseline) displays so as to equate the total number of repeated displays across experiments. In Experiment 1d, repeated and nonrepeated displays were presented in longer streaks of trials, thus establishing a stable environment of sequences of repeated displays. Our results showed that the buildup of contextual cueing was expedited in the statistically rich Experiments 1b and 1d, relative to the baseline Experiment 1a. Further, contextual cueing was entirely absent when repeated displays occurred in the minority of trials (Experiment 1c). Together, these findings suggest that contextual cueing is modulated by observers' assumptions about the reliability of search environments.
Sensory prediction errors are fundamental brain responses that signal a violation of expectation in either the internal or external sensory environment, and are therefore crucial for survival and adaptive behaviour. P...
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Sensory prediction errors are fundamental brain responses that signal a violation of expectation in either the internal or external sensory environment, and are therefore crucial for survival and adaptive behaviour. Patients with schizophrenia show deficits in these internal and external sensory prediction errors, which can be measured using electroencephalography (EEG) components such as N1 and mismatch negativity (MMN), respectively. New evidence suggests that these deficits in sensory prediction errors are more widely distributed on a continuum of psychosis, whereas psychotic experiences exist to varying degrees throughout the general population. In this paper, we review recent findings in sensory prediction errors in the auditory domain across the continuum of psychosis, and discuss these in light of the predictive coding hypothesis. (c) 2017 Elsevier B.V. All rights reserved.
The brain draws on knowledge of statistical structure in the environment to facilitate detection of new events. Understanding the nature of this representation is a key challenge in sensory neuroscience. Specifically,...
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The brain draws on knowledge of statistical structure in the environment to facilitate detection of new events. Understanding the nature of this representation is a key challenge in sensory neuroscience. Specifically, it is unknown whether real-time perception of rapidly-unfolding sensory signals is driven by a coarse or detailed representation of the proximal stimulus history. We recorded electroencephalography brain responses to frequency outliers in regularly-patterned (REG) versus random (RAND) tone-pip sequences which were generated anew on each trial. REG and RAND sequences were matched in frequency content and span, only differing in the specific order of the tone-pips. Stimuli were very rapid, limiting conscious reasoning in favour of automatic processing of regularity. Listeners were naive and performed an incidental visual task. Outliers within REG evoked a larger response than matched outliers in RAND. These effects arose rapidly (within 80 msec) and were underpinned by distinct sources from those classically associated with frequency-based deviance detection. These findings are consistent with the notion that the brain continually maintains a detailed representation of ongoing sensory input and that this representation shapes the processing of incoming information. Predominantly auditory-cortical sources code for frequency deviance whilst frontal sources are associated with tracking more complex sequence structure. (C) 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license
Given that eye movement control can be framed as an inferential process, how are the requisite forces generated to produce anticipated or desired fixation? Starting from a generative model based on simple Newtonian eq...
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Given that eye movement control can be framed as an inferential process, how are the requisite forces generated to produce anticipated or desired fixation? Starting from a generative model based on simple Newtonian equations of motion, we derive a variational solution to this problem and illustrate the plausibility of its implementation in the oculomotor brainstem. We show, through simulation, that the Bayesian filtering equations that implement 'planning as inference' can generate both saccadic and smooth pursuit eye movements. Crucially, the associated message passing maps well onto the known connectivity and neuroanatomy of the brainstem and the changes in these messages over time are strikingly similar to single unit recordings of neurons in the corresponding nuclei. Furthermore, we show that simulated lesions to axonal pathways reproduce eye movement patterns of neurological patients with damage to these tracts.
Objective: The study sought to assess the presence of auditory N100 gating deficits in patients with schizophrenia by meta-analysis. Methods: Literature was screened for studies on patients with schizophrenia that use...
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Objective: The study sought to assess the presence of auditory N100 gating deficits in patients with schizophrenia by meta-analysis. Methods: Literature was screened for studies on patients with schizophrenia that used the paired-click paradigm and reported N100 data. Both electroencephalographic and magnetoencephalographic studies were considered. N100 gating measures as well as the N100 amplitudes to the initial and repeated stimulus were extracted and subjected to a meta-analysis. Results: The literature research revealed 29 studies, reporting either N100 gating or N100 amplitude measures in paired-click experiments. Patients with schizophrenia exhibited less N100 gating than healthy controls across studies (mean g = -0.405, SE = 0.051). However, what appeared as a gating deficit in patients was due to reduced N100 amplitudes to the initial stimulus in this group (mean g = 0.610, SE = 0.075). Patients and controls did not differ in their N100 amplitudes to the repeated stimulus (mean g = 0.042, SE = 0.066). Conclusion: There is no evidence for an auditory N100 gating deficit in schizophrenia, but for an impaired N100 response recovery. Significance: Previous findings on impaired N100 gating in schizophrenia patients reflect deficient processing of auditory salience rather than defective inhibition of repeating redundant auditory stimulation. (C) 2018 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.
In many scientific, medical, and defense applications of image/video compression, an l(infinity) error bound is required. However, pure l(infinity)-optimized image coding, colloquially known as near-lossless image cod...
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In many scientific, medical, and defense applications of image/video compression, an l(infinity) error bound is required. However, pure l(infinity)-optimized image coding, colloquially known as near-lossless image coding, is prone to structured errors such as contours and speckles if the bit rate is not sufficiently high;moreover, most of the previous l(infinity)-based image coding methods suffer from poor rate control. In contrast, the l(2) error metric aims for average fidelity and hence preserves the subtlety of smooth waveforms better than the l(infinity) error metric and it offers fine granularity in rate control, but pure l(2)-based image coding methods (e.g., JPEG 2000) cannot bound individual errors as the l(infinity)-based methods can. This paper presents a new compression approach to retain the benefits and circumvent the pitfalls of the two error metrics. A common approach of near-lossless image coding is to embed into a DPCM prediction loop a uniform scalar quantizer of residual errors. The said uniform scalar quantizer is replaced, in the proposed new approach, by a set of context-based l(2)-optimized quantizers. The optimization criterion is to minimize a weighted sum of the l(2) distortion and the entropy while maintaining a strict l(infinity) error bound. The resulting method obtains good rate-distortion performance in both l(2) and l(infinity) metrics and also increases the rate granularity. Compared with JPEG 2000, the new method not only guarantees lower l(infinity) error for all bit rates, but also it achieves higher PSNR for relatively high bit rates.
Objective: Dyspnea perception is distorted in patients with medically unexplained dyspnea. The goals of this study were 1) to replicate these results in patients with fibromyalgia and/or chronic fatigue syndrome (CFS)...
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Objective: Dyspnea perception is distorted in patients with medically unexplained dyspnea. The goals of this study were 1) to replicate these results in patients with fibromyalgia and/or chronic fatigue syndrome (CFS), and 2) to investigate predictors of distorted symptom perception within the patient group, with a focus on negative affectivity (NA), psychiatric comorbidity and somatic symptom severity. Methods: Seventy-three patients diagnosed with fibromyalgia and/or CFS and 38 healthy controls (HC) completed a rebreathing paradigm, consisting of a baseline (60 s of room air), a rebreathing phase (150 s, gradually increasing ventilation, partial pressure of CO2 in the blood, and self-reported dyspnea), and a recovery phase (150 s of room air). Dyspnea, respiratory flow and FetCO(2) levels were measured continuously. Results: Patients reported more dyspnea than HC in the recovery phase (p = 0.039), but no differences between patients and HC were found in the baseline (p = 0.07) or rebreathing phase (p = 0.17). No significant differences between patients and HC were found in physiological reactivity. Within the patient group, the effect in the recovery phase was predicted by somatic symptom severity (p = 0.046), but not by negative affectivity or by the number of psychiatric comorbidities. Conclusion: This study extended earlier findings in patients with medically unexplained dyspnea to patients with fibromyalgia and CFS. This suggests that altered symptom perception is a non-symptom-specific mechanism underlying functional somatic syndromes in general, particularly in patients with high levels of somatic symptom severity. The results are discussed in a predictive coding framework of symptom perception.
Objective: The current article set out to review all research conducted to date investigating prospective memory (PM) in autism. Method: All studies on PM in autism are first described, followed by a critical review a...
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Objective: The current article set out to review all research conducted to date investigating prospective memory (PM) in autism. Method: All studies on PM in autism are first described, followed by a critical review and discussion of experimental findings within the multiprocess framework. PM in autism is then considered through an embodied predictive-coding account of autism. Results: Overall, despite somewhat inconsistent methodologies, a general deficit in PM in autism is observed, with evidence mostly in line with the multiprocess framework. That is, for tasks that are high in cognitive and attentional demand (e.g. time-based tasks;event-based cues of non-focality or low salience) PM performance of autistic participants is impaired. Building upon previous work in predictive-coding, and the way in which expected precision modulates attention, we postulate mechanisms that underpin PM and the potential deficits seen in autism. Furthermore, a unifying predictive-coding account of autism is extended under embodied predictive-coding models, to show how a predictive-coding impairment accounts not only for characteristic autistic difficulties, but also for commonly found differences in autistic movement. Conclusions: We show how differences in perception and action, core to the development of autism, lead directly to problems seen in PM. Using this link between movement and PM, we then put forward a number of holistic, embodied interventions to support PM in autism.
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