scholarly journals Decoding of EEG signals reveals non-uniformities in the neural geometry of colour

2021 ◽  
Author(s):  
Tushar Chauhan ◽  
Ivana Jakovljev ◽  
Lindsay Thompson ◽  
Sophie Wuerger ◽  
Jasna Martinovic
Keyword(s):  
Luminance Contrast ◽  
Neural Correlates ◽  
Stimulus Onset ◽  
Neural Code ◽  
Mutual Distance ◽  
Eeg Signals ◽  
High Luminance ◽  
Unique Hues ◽  
Open Question ◽  
Colour Signals

The idea of colour opponency maintains that colour vision arises through the comparison of two chromatic mechanisms, red versus green (RG) and yellow versus blue (YB). The four unique hues, red, green, blue, and yellow, are assumed to appear at the null points of these the two chromatic systems. However, whether unique hues have a distinct signature that can be reliably discerned in neural activity is still an open question. Here we hypothesise that, if unique hues represent a tractable cortical state, they should elicit more robust activity compared to non-unique hues. We use a spatiotemporal decoding approach to reconstruct an activation space for a set of unique and intermediate hues across a range of luminance values. We show that electroencephalographic (EEG) responses carry robust information about isoluminant unique hues within a 100-300 ms window from stimulus onset. Decoding is possible in both passive and active viewing tasks, but is compromised when concurrent high luminance contrast is added to the colour signals. The efficiency of hue decoding is not entirely predicted by their mutual distance in a nominally uniform colour space. Instead, the encoding space shows pivotal non-uniformities which suggest that anisotropies in neurometric hue-spaces are likely to represent perceptual unique hues. Furthermore, the neural code for hue temporally coincides with the neural code for luminance contrast, thus explaining why potential neural correlates of unique hues have remained so elusive until now.

An Efficient Deep Learning Paradigm for Deceit Identification Test on EEG Signals

2021 ◽  
Vol 12 (3) ◽  
pp. 1-20
Author(s):  
Damodar Reddy Edla ◽  
Shubham Dodia ◽  
Annushree Bablani ◽  
Venkatanareshbabu Kuppili
Keyword(s):  
Brain Computer Interface ◽  
Wavelet Packet ◽  
Stimulus Onset ◽  
Computer Interface ◽  
Band Pass Filter ◽  
Eeg Signals ◽  
Pass Filter ◽  
Eeg Data ◽  
Identification Test ◽  
Band Pass

Brain-Computer Interface is the collaboration of the human brain and a device that controls the actions of a human using brain signals. Applications of brain-computer interface vary from the field of entertainment to medical. In this article, a novel Deceit Identification Test is proposed based on the Electroencephalogram signals to identify and analyze the human behavior. Deceit identification test is based on P300 signals, which have a positive peak from 300 ms to 1,000 ms of the stimulus onset. The aim of the experiment is to identify and classify P300 signals with good classification accuracy. For preprocessing, a band-pass filter is used to eliminate the artifacts. The feature extraction is carried out using “symlet” Wavelet Packet Transform (WPT). Deep Neural Network (DNN) with two autoencoders having 10 hidden layers each is applied as the classifier. A novel experiment is conducted for the collection of EEG data from the subjects. EEG signals of 30 subjects (15 guilty and 15 innocent) are recorded and analyzed during the experiment. BrainVision recorder and analyzer are used for recording and analyzing EEG signals. The model is trained for 90% of the dataset and tested for 10% of the dataset and accuracy of 95% is obtained.

Motivational Salience Guides Attention to Valuable and Threatening Stimuli: Evidence from Behavior and Functional Magnetic Resonance Imaging

2021 ◽  
pp. 1-21
Author(s):  
Haena Kim ◽  
Namrata Nanavaty ◽  
Humza Ahmed ◽  
Vani A. Mathur ◽  
Brian A. Anderson
Keyword(s):  
Magnetic Resonance Imaging ◽  
Attentional Control ◽  
Underlying Mechanism ◽  
Neural Correlates ◽  
Functional Magnetic Resonance ◽  
Resonance Imaging ◽  
Approach And Avoidance ◽  
Motivational Salience ◽  
Opposing Effects ◽  
Open Question

Abstract Rewarding and aversive outcomes have opposing effects on behavior, facilitating approach and avoidance, although we need to accurately anticipate each type of outcome to behave effectively. Attention is biased toward stimuli that have been learned to predict either type of outcome, and it remains an open question whether such orienting is driven by separate systems for value- and threat-based orienting or whether there exists a common underlying mechanism of attentional control driven by motivational salience. Here, we provide a direct comparison of the neural correlates of value- and threat-based attentional capture after associative learning. Across multiple measures of behavior and brain activation, our findings overwhelmingly support a motivational salience account of the control of attention. We conclude that there exists a core mechanism of experience-dependent attentional control driven by motivational salience and that prior characterizations of attention as being value driven or supporting threat monitoring need to be revisited.

Detection of colour signals in objects defined by luminance contrast

2012 ◽  
Vol 90 ◽  
pp. 0-0
Author(s):  
J HICKEY ◽  
M RODRIGUEZ-CARMONA ◽  
JL BARBUR
Keyword(s):  
Luminance Contrast ◽  
Colour Signals

scholarly journals Outline and surface disruption in animal camouflage

2008 ◽  
Vol 276 (1657) ◽  
pp. 781-786 ◽  
Author(s):  
Martin Stevens ◽  
Isabel S Winney ◽  
Abi Cantor ◽  
Julia Graham
Keyword(s):  
Body Shape ◽  
Luminance Contrast ◽  
The Body ◽  
Maximum Effect ◽  
High Contrast ◽  
High Luminance ◽  
Effective Surface ◽  
Avian Predators ◽  
Disruptive Coloration ◽  
Visual Mechanism

Camouflage is an important strategy in animals to prevent predation. This includes disruptive coloration, where high-contrast markings placed at an animal's edge break up the true body shape. Successful disruption may also involve non-marginal markings found away from the body outline that create ‘false edges’ more salient than the true body form (‘surface disruption’). However, previous work has focused on breaking up the true body outline, not on surface disruption. Furthermore, while high contrast may enhance disruption, it is untested where on the body different contrasts should be placed for maximum effect. We used artificial prey presented to wild avian predators in the field, to determine the effectiveness of surface disruption, and of different luminance contrast placed in different prey locations. Disruptive coloration was no more effective when comprising high luminance contrast per se , but its effectiveness was dramatically increased with high-contrast markings placed away from the body outline, creating effective surface disruption. A model of avian visual edge processing showed that surface disruption does not make object detection more difficult simply by creating false edges away from the true body outline, but its effect may also be based on a different visual mechanism. Our study has implications for whether animals can combine disruptive coloration with other ‘conspicuous’ signalling strategies.

Different Electrophysiological Correlates of Visual Awareness for Detection and Identification

2017 ◽  
Vol 29 (9) ◽  
pp. 1621-1631 ◽  
Author(s):  
Mika Koivisto ◽  
Simone Grassini ◽  
Niina Salminen-Vaparanta ◽  
Antti Revonsuo
Keyword(s):  
Visual Awareness ◽  
Neural Correlates ◽  
Stimulus Onset ◽  
Early Elementary ◽  
Neural Correlates Of Consciousness ◽  
Detection And Identification

Detecting the presence of an object is a different process than identifying the object as a particular object. This difference has not been taken into account in designing experiments on the neural correlates of consciousness. We compared the electrophysiological correlates of conscious detection and identification directly by measuring ERPs while participants performed either a task only requiring the conscious detection of the stimulus or a higher-level task requiring its conscious identification. Behavioral results showed that, even if the stimulus was consciously detected, it was not necessarily identified. A posterior electrophysiological signature 200–300 msec after stimulus onset was sensitive for conscious detection but not for conscious identification, which correlated with a later widespread activity. Thus, we found behavioral and neural evidence for elementary visual experiences, which are not yet enriched with higher-level knowledge. The search for the mechanisms of consciousness should focus on the early elementary phenomenal experiences to avoid the confounding effects of higher-level processes.

scholarly journals Physiological Correlates of Sensory Consciousness: Evidence for a Generalized Awareness Negativity

2021 ◽  
Author(s):  
Cole Dembski ◽  
Christof Koch ◽  
Michael Pitts
Keyword(s):  
Experimental Studies ◽  
Neural Correlates ◽  
Stimulus Onset ◽  
Convincing Evidence ◽  
Future Research ◽  
Neural Signals ◽  
Tactile Stimuli ◽  
Neurological Patients ◽  
Sensory Cortices ◽  
Sensory Consciousness

We critically review the recent literature on six EEG and MEG markers of the neural correlates of consciousness (NCC) for visual, auditory and tactile stimuli in neurotypical volunteers and neurological patients. After ruling out four of these as candidate NCC, we focus on two prominent evoked signals: an early, modality-specific negativity, termed the visual or auditory awareness negativity (VAN and AAN, respectively) and a late, modality-independent positivity termed the P3b. More than twelve diverse experimental studies found that the P3b is absent despite consciously seeing, hearing, or feeling stimuli, ruling out the P3b as a true NCC. In contrast, no convincing evidence for a dissociation between the awareness negativities and consciousness has been reported thus far. Furthermore, there is evidence for an equivalent signal in the tactile domain, which we term the somatosensory awareness negativity (SAN). These three neural signals are usually maximal on the side of the scalp contralateral to the evoking stimulus, above the associated sensory cortices. We conclude that the data from these three modalities is consistent with a generalized awareness negativity (GAN) correlated with perceptual consciousness that arises 120-200 ms following stimulus onset and originates from the underlying sensory cortices. The identification of this GAN points towards new, promising avenues for future research and raises an array of concrete questions that can be empirically investigated.

scholarly journals Growing Shapes with a Generalised Model from Neural Correlates of Visual Discrimination

2021 ◽  
pp. 68-78
Author(s):  
Pierre Cutellic
Keyword(s):  
Design Process ◽  
Visual Discrimination ◽  
Event Related Potentials ◽  
Visual Cognition ◽  
Neural Correlates ◽  
Classification Models ◽  
Eeg Signals ◽  
Related Potentials ◽  
Design Solutions ◽  
Singular Individual

AbstractThis paper focuses on the application of visual Event-Related Potentials (ERP) in better generalisations for design and architectural modelling. It makes use of previously built techniques and trained models on EEG signals of a singular individual and observes the robustness of advanced classification models to initiate the development of presentation and classification techniques for enriched visual environments by developing an iterative and generative design process of growing shapes. The pursued interest is to observe if visual ERP as correlates of visual discrimination can hold in structurally similar, but semantically different, experiments and support the discrimination of meaningful design solutions. Following bayesian terms, we will coin this endeavour a Design Belief and elaborate a method to explore and exploit such features decoded from human visual cognition.

The N2pc as an Electrophysiological Correlate of Attention in Change Blindness

2009 ◽  
Vol 23 (2) ◽  
pp. 43-51 ◽  
Author(s):  
Andrea Schankin ◽  
Dirk Hagemann ◽  
Edmund Wascher
Keyword(s):  
Change Blindness ◽  
Visual Awareness ◽  
Neural Correlates ◽  
Stimulus Onset ◽  
Attentional Processing ◽  
Electrophysiological Activity ◽  
Cortical Areas ◽  
Physically Identical ◽  
Visual Cortical ◽  
Electrophysiological Correlate

Changes between two successively presented pictures are hard to detect when their presentation is interrupted by a blank (change blindness). This task is well established for investigating the neural correlates of visual awareness. It allows the comparison of electrophysiological activity evoked by physically identical trials in which the change was detected versus trials in which the change remained unnoticed. One possible correlate of aware processing is the N2pc component, an increased negative activity, contralateral to a processed stimulus between 200–300 ms after stimulus onset. However, this component has been also assigned to the allocation of attention. In two experiments, an N2pc was observed for detected changes. This component was markedly reduced for undetected changes and even more if participants reported a change that was not present (imagined change). These results suggest that the N2pc rather reflects attentional processing of stimuli in visual cortical areas than the actual aware representation.

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