scholarly journals Top–Down Control of Alpha Phase Adjustment in Anticipation of Temporally Predictable Visual Stimuli

2018 ◽  
Vol 30 (8) ◽  
pp. 1157-1169 ◽  
Author(s):  
Rodolfo Solís-Vivanco ◽  
Ole Jensen ◽  
Mathilde Bonnefond
Keyword(s):  
Visual Processing ◽  
Visual Information ◽  
Alpha Phase ◽  
Stimulus Onset ◽  
Gamma Activity ◽  
Alpha Power ◽  
Top Down ◽  
Alpha Oscillations ◽  
Phase Adjustment ◽  
Visual Areas

Alpha oscillations (8–14 Hz) are proposed to represent an active mechanism of functional inhibition of neuronal processing. Specifically, alpha oscillations are associated with pulses of inhibition repeating every ∼100 msec. Whether alpha phase, similar to alpha power, is under top–down control remains unclear. Moreover, the sources of such putative top–down phase control are unknown. We designed a cross-modal (visual/auditory) attention study in which we used magnetoencephalography to record the brain activity from 34 healthy participants. In each trial, a somatosensory cue indicated whether to attend to either the visual or auditory domain. The timing of the stimulus onset was predictable across trials. We found that, when visual information was attended, anticipatory alpha power was reduced in visual areas, whereas the phase adjusted just before the stimulus onset. Performance in each modality was predicted by the phase of the alpha oscillations previous to stimulus onset. Alpha oscillations in the left pFC appeared to lead the adjustment of alpha phase in visual areas. Finally, alpha phase modulated stimulus-induced gamma activity. Our results confirm that alpha phase can be top–down adjusted in anticipation of predictable stimuli and improve performance. Phase adjustment of the alpha rhythm might serve as a neurophysiological resource for optimizing visual processing when temporal predictions are possible and there is considerable competition between target and distracting stimuli.

Working Memory Processes Are Mediated by Local and Long-range Synchronization of Alpha Oscillations

2013 ◽  
Vol 25 (8) ◽  
pp. 1343-1357 ◽  
Author(s):  
Maite Crespo-Garcia ◽  
Diego Pinal ◽  
Jose L. Cantero ◽  
Fernando Díaz ◽  
Montserrat Zurrón ◽  
...  
Keyword(s):  
Working Memory ◽  
Long Range ◽  
Alpha Phase ◽  
Alpha Power ◽  
Phase Synchrony ◽  
Top Down ◽  
Alpha Oscillations ◽  
Memory Processes ◽  
Time Frequency ◽  
Cortical Regions

Different cortical dynamics of alpha oscillations (8–13 Hz) have been associated with increased working memory load, which have been mostly interpreted as a neural correlate of functional inhibition. This study aims at determining whether different manifestations of load-dependent amplitude and phase dynamics in the alpha band can coexist over different cortical regions. To address this question, we increased information load by manipulating the number and spatial configuration of domino spots. Time–frequency analysis of EEG source activity revealed (i) load-independent increases of both alpha power and interregional alpha-phase synchrony within task-irrelevant, posterior cortical regions and (ii) load-dependent decreases of alpha power over areas of the left pFC and bilateral posterior parietal cortex (PPC) preceded in time by load-dependent decreases of alpha-phase synchrony between the left pFC and the left PPC. The former results support the role of alpha oscillations in inhibiting irrelevant sensorimotor processing, whereas the latter likely reflect release of parietal task-relevant areas from top–down inhibition with load increase. This interpretation found further support in a significant latency shift of 15 msec from pFC to the PPC. Together, these results suggest that amplitude and phase alpha dynamics in both local and long-range cortical networks reflect different neural mechanisms of top–down control that might be crucial in mediating the different working memory processes.

scholarly journals Top-down inhibition of irrelevant information indexed by alpha rhythms is disrupted in migraine

2021 ◽  
Author(s):  
Rémy Masson ◽  
Hesham A ElShafei ◽  
Geneviève Demarquay ◽  
Lesly Fornoni ◽  
Yohana Lévêque ◽  
...  
Keyword(s):  
Cognitive Processing ◽  
Gamma Activity ◽  
Auditory Target ◽  
Alpha Power ◽  
Top Down ◽  
Significant Group ◽  
Bottom Up ◽  
Power Increase ◽  
Visual Areas ◽  
Healthy Participants

There is growing evidence that migraine is associated with attentional abnormalities, both during and outside migraine attacks, which would impact the cognitive processing of sensory stimulation. However, these attention alterations are poorly characterized and their neurophysiological basis is still unclear. Nineteen migraineurs without aura and nineteen healthy participants were recruited to perform a task which used visually-cued auditory targets and distracting sounds to evaluate conjointly top-down and bottom-up attention mechanisms. Magnetoencephalography (MEG) signals were recorded. We investigated anticipatory alpha activity (power increase and decrease) and distractor-induced gamma activity as markers for top-down (inhibition and facilitation) and bottom-up attention, respectively. Compared to healthy participants, migraineurs presented a significantly less prominent alpha power increase in visual areas in anticipation of the auditory target, indexing a reduced inhibition of task-irrelevant visual areas. However, there was no significant group difference regarding the alpha power decrease in the relevant auditory cortices in anticipation of the target, nor regarding the distractor-induced gamma power increase in the ventral attention network. These results in the alpha band suggest that top-down inhibitory processes in the visual cortices are deficient in migraine but there is no clear evidence supporting a disruption of top-down facilitatory attentional processes. This relative inability to suppress irrelevant sensory information may be underlying the self-reported increased distractibility and contribute to sensory disturbances in migraine.

Power and Phase of Alpha Oscillations Reveal an Interaction between Spatial and Temporal Visual Attention

2017 ◽  
Vol 29 (3) ◽  
pp. 480-494 ◽  
Author(s):  
Sayeed A. D. Kizuk ◽  
Kyle E. Mathewson
Keyword(s):  
Visual Processing ◽  
Alpha Phase ◽  
Alpha Power ◽  
Alpha Band ◽  
Target Onset ◽  
Alpha Oscillations ◽  
Perceptual Performance ◽  
Neural Entrainment ◽  
Sensory Activity ◽  
Bias Attention

Oscillatory brain rhythms can bias attention via phase and amplitude changes, which modulate sensory activity, biasing information to be processed or ignored. Alpha band (7–14 Hz) oscillations lateralize with spatial attention and rhythmically inhibit visual activity and awareness through pulses of inhibition. Here we show that human observers' awareness of spatially unattended targets is dependent on both alpha power and alpha phase at target onset. Following a predictive directional cue, alpha oscillations were entrained bilaterally using repetitive visual stimuli. Subsequently, we presented either spatially cued or uncued targets at SOAs either validly or invalidly predicted in time by the entrainers. Temporal validity maximally modulated perceptual performance outside the spatial focus of attention and was associated with both increased alpha power and increased neural entrainment of phase in the hemisphere processing spatially unattended information. The results demonstrate that alpha oscillations represent a pulsating inhibition, which impedes visual processing for unattended space.

scholarly journals The Neurophysiology of Backward Visual Masking: Information Analysis

1999 ◽  
Vol 11 (3) ◽  
pp. 300-311 ◽  
Author(s):  
Edmund T. Rolls ◽  
Martin J. Tovée ◽  
Stefano Panzeri
Keyword(s):  
Visual Processing ◽  
Visual Information ◽  
Computational Models ◽  
Direct Evidence ◽  
Visual Masking ◽  
Neuronal Response ◽  
Short Soas ◽  
Stimulus Onset ◽  
Backward Masking ◽  
Neuronal Responses

Backward masking can potentially provide evidence of the time needed for visual processing, a fundamental constraint that must be incorporated into computational models of vision. Although backward masking has been extensively used psychophysically, there is little direct evidence for the effects of visual masking on neuronal responses. To investigate the effects of a backward masking paradigm on the responses of neurons in the temporal visual cortex, we have shown that the response of the neurons is interrupted by the mask. Under conditions when humans can just identify the stimulus, with stimulus onset asynchronies (SOA) of 20 msec, neurons in macaques respond to their best stimulus for approximately 30 msec. We now quantify the information that is available from the responses of single neurons under backward masking conditions when two to six faces were shown. We show that the information available is greatly decreased as the mask is brought closer to the stimulus. The decrease is more marked than the decrease in firing rate because it is the selective part of the firing that is especially attenuated by the mask, not the spontaneous firing, and also because the neuronal response is more variable at short SOAs. However, even at the shortest SOA of 20 msec, the information available is on average 0.1 bits. This compares to 0.3 bits with only the 16-msec target stimulus shown and a typical value for such neurons of 0.4 to 0.5 bits with a 500-msec stimulus. The results thus show that considerable information is available from neuronal responses even under backward masking conditions that allow the neurons to have their main response in 30 msec. This provides evidence for how rapid the processing of visual information is in a cortical area and provides a fundamental constraint for understanding how cortical information processing operates.

Top-Down Predictions Determine Perceptions

2017 ◽  
Author(s):  
Martin V. Butz ◽  
Esther F. Kutter
Keyword(s):  
Graphical Models ◽  
Information Integration ◽  
Visual Processing ◽  
Visual Information ◽  
Generative Models ◽  
Sources Of Information ◽  
Multiple Sources ◽  
Top Down ◽  
Bottom Up ◽  
The Brain

While bottom-up visual processing is important, the brain integrates this information with top-down, generative expectations from very early on in the visual processing hierarchy. Indeed, our brain should not be viewed as a classification system, but rather as a generative system, which perceives something by integrating sensory evidence with the available, learned, predictive knowledge about that thing. The involved generative models continuously produce expectations over time, across space, and from abstracted encodings to more concrete encodings. Bayesian information processing is the key to understand how information integration must work computationally – at least in approximation – also in the brain. Bayesian networks in the form of graphical models allow the modularization of information and the factorization of interactions, which can strongly improve the efficiency of generative models. The resulting generative models essentially produce state estimations in the form of probability densities, which are very well-suited to integrate multiple sources of information, including top-down and bottom-up ones. A hierarchical neural visual processing architecture illustrates this point even further. Finally, some well-known visual illusions are shown and the perceptions are explained by means of generative, information integrating, perceptual processes, which in all cases combine top-down prior knowledge and expectations about objects and environments with the available, bottom-up visual information.

Cortical Projection Topography of the Human Splenium: Hemispheric Asymmetry and Individual Differences

2010 ◽  
Vol 22 (8) ◽  
pp. 1662-1669 ◽  
Author(s):  
Mary Colvin Putnam ◽  
Megan S. Steven ◽  
Karl W. Doron ◽  
Adam C. Riggall ◽  
Michael S. Gazzaniga
Keyword(s):  
Visual Processing ◽  
Visual Information ◽  
Hemispheric Asymmetry ◽  
Right Hemisphere ◽  
Diffusion Tensor ◽  
Cortical Projection ◽  
Interhemispheric Communication ◽  
Posterior Portion ◽  
Interhemispheric Connectivity ◽  
Visual Areas

The corpus callosum is the largest white matter pathway in the human brain. The most posterior portion, known as the splenium, is critical for interhemispheric communication between visual areas. The current study employed diffusion tensor imaging to delineate the complete cortical projection topography of the human splenium. Homotopic and heterotopic connections were revealed between the splenium and the posterior visual areas, including the occipital and the posterior parietal cortices. In nearly one third of participants, there were homotopic connections between the primary visual cortices, suggesting interindividual differences in splenial connectivity. There were also more instances of connections with the right hemisphere, indicating a hemispheric asymmetry in interhemispheric connectivity within the splenium. Combined, these findings demonstrate unique aspects of human interhemispheric connectivity and provide anatomical bases for hemispheric asymmetries in visual processing and a long-described hemispheric asymmetry in speed of interhemispheric communication for visual information.

scholarly journals Attention and Temporal Expectations Modulate Power, Not Phase, of Ongoing Alpha Oscillations

2015 ◽  
Vol 27 (8) ◽  
pp. 1573-1586 ◽  
Author(s):  
Rosanne M. van Diepen ◽  
Michael X Cohen ◽  
Damiaan Denys ◽  
Ali Mazaheri
Keyword(s):  
Phase Angle ◽  
Phase Locking ◽  
Auditory Target ◽  
Alpha Power ◽  
Visual Condition ◽  
Top Down ◽  
Alpha Oscillations ◽  
Alpha Oscillation ◽  
Sensory Cortices ◽  
Phase Angles

The perception of near-threshold visual stimuli has been shown to depend in part on the phase (i.e., time in the cycle) of ongoing alpha (8–13 Hz) oscillations in the visual cortex relative to the onset of that stimulus. However, it is currently unknown whether the phase of the ongoing alpha activity can be manipulated by top–down factors such as attention or expectancy. Using three variants of a cross-modal attention paradigm with constant predictable stimulus onsets, we examined if cues signaling to attend to either the visual or the auditory domain influenced the phase of alpha oscillations in the associated sensory cortices. Importantly, intermixed in all three experiments, we included trials without a target to estimate the phase at target presentation without contamination from the early evoked responses. For these blank trials, at the time of expected target and distractor onset, we examined (1) the degree of the uniformity in phase angles across trials, (2) differences in phase angle uniformity compared with a pretarget baseline, and (3) phase angle differences between visual and auditory target conditions. Across all three experiments, we found that, although the cues induced a modulation in alpha power in occipital electrodes, neither the visual condition nor the auditory cue condition induced any significant phase-locking across trials during expected target or distractor presentation. These results suggest that, although alpha power can be modulated by top–down factors such as attention and expectation, the phase of the ongoing alpha oscillation is not under such control.

scholarly journals REPRESENTATION OF 3-D VOLUMETRIC OBJECT FROM THE PANTOMIME EFFECT AND SHADING CUES IN HUMAN BRAIN

2007 ◽  
Vol 21 (08) ◽  
pp. 1307-1322
Author(s):  
QI ZHANG ◽  
KEN MOGI
Keyword(s):  
Human Brain ◽  
Visual Processing ◽  
Visual Information ◽  
Binocular Disparity ◽  
Object Perception ◽  
Human Beings ◽  
Brain Areas ◽  
Human Ability ◽  
Visual Areas ◽  
Visual Phenomenon

Human ability to process visual information of outside world is yet far ahead of man-made systems in accuracy and speed. In particular, human beings can perceive 3-D object from various cues, such as binocular disparity and monocular shading cues. Understanding of the mechanism of human visual processing will lead to a breakthrough in creating artificial visual systems. Here, we study the human 3-D volumetric object perception that is induced by a visual phenomenon named as the pantomime effect and by the monocular shading cues. We measured human brain activities using fMRI when the subjects were observing the visual stimuli. A coordinated system of brain areas, including those in the prefrontal and parietal cortex, in addition to the occipital visual areas was found to be involved in the volumetric object perception.

scholarly journals Pre-Stimulus Alpha-Band Phase Gates Afferent Visual Cortex Responses

2021 ◽  
Author(s):  
Wei Dou ◽  
Audrey Morrow ◽  
Luca Iemi ◽  
Jason Samaha
Keyword(s):  
Visual Cortex ◽  
Visual Processing ◽  
Time Window ◽  
Event Related Potentials ◽  
Alpha Phase ◽  
Alpha Activity ◽  
Alpha Band ◽  
Visual Responses ◽  
Alpha Oscillations ◽  
Related Potentials

The neurogenesis of alpha-band (8-13 Hz) activity has been characterized across many different animal experiments. However, the functional role that alpha oscillations play in perception and behavior has largely been attributed to two contrasting hypotheses, with human evidence in favor of either (or both or neither) remaining sparse. On the one hand, alpha generators have been observed in relay sectors of the visual thalamus and are postulated to phasically inhibit afferent visual input in a feedforward manner 1-4. On the other hand, evidence also suggests that the direction of influence of alpha activity propagates backwards along the visual hierarchy, reflecting a feedback influence upon the visual cortex 5-9. The primary source of human evidence regarding the role of alpha phase in visual processing has been on perceptual reports 10-16, which could be modulated either by feedforward or feedback alpha activity. Thus, although these two hypotheses are not mutually exclusive, human evidence clearly supporting either one is lacking. Here, we present human subjects with large, high-contrast visual stimuli that elicit robust C1 event-related potentials (ERP), which peak between 70-80 milliseconds post-stimulus and are thought to reflect afferent primary visual cortex (V1) input 17-20. We find that the phase of ongoing alpha oscillations modulates the global field power (GFP) of the EEG during this first volley of stimulus processing (the C1 time-window). On the standard assumption 21-23 that this early activity reflects postsynaptic potentials being relayed to visual cortex from the thalamus, our results suggest that alpha phase gates visual responses during the first feed-forward sweep of processing.

scholarly journals Postdiction: when temporal regularity drives space perception through pre-stimulus alpha oscillations

2021 ◽  
Author(s):  
Laetitia Grabot ◽  
Christoph Kayser ◽  
Virginie van Wassenhove
Keyword(s):  
Spatial Perception ◽  
Space Perception ◽  
Slow Motion ◽  
Alpha Phase ◽  
Alpha Power ◽  
Alpha Oscillations ◽  
Brain Responses ◽  
Illusory Perception ◽  
Neural Underpinnings ◽  
Human Participants

AbstractDuring postdiction, the last stimulus of a sequence changes the perception of the preceding ones: in the rabbit illusion, a three-flash series presented regularly in time, but not in space, is – illusory - perceived as spatially regular. Such a reorganization of (spatial) perception could be driven by internal priors, e.g. favoring slow motion for the rabbit illusion. Although postdiction is a ubiquitous phenomenon, its neural underpinnings remain poorly understood. Here, we focused on the role of priors during postdiction and hypothesized that these could be reflected by alpha oscillations (8-12Hz), previously observed to correlate with idiosyncratic biases. We presented human participants with ambiguous visual stimuli that elicited the rabbit illusion on about half the trials, allowing us to contrast MEG-EEG brain responses to the same physical events causing distinct percepts. Given that a strong prior will increase the overall probability of perceiving the illusion, we used the percentage of perceived illusion as a proxy for an individual’s prior. We found that high fronto-parietal alpha power was associated with perceiving the sequence according to individual biases: participants with high susceptibility to the illusion would report the illusion, while participants with low susceptibility would report the veridical sequence. Additionally, we found that pre-stimulus alpha phase in occipital and frontal areas dissociated illusory from non-illusory trials. These results point to a dissociated relation of the power and timing of alpha band activity to illusory perception, with power reflecting prior expectations and phase influencing behavioral performance, potentially due to the modulation of sensory uncertainty.Significance StatementLate events may sometimes influence how earlier events are perceived, as if the arrow of time was reversed in the brain. This surprising phenomenon, called postdiction, is observed in the rabbit illusion, and highlights a predominant mechanism for perceptual processes. Perception builds up from the combination of prior expectations with incoming sensory evidence, which takes time. We showed that pre-stimulus neural activity, and more specifically alpha oscillations (8-12Hz), play a double role in postdiction. Fronto-parietal alpha power reflects individual prior expectation, while occipital and frontal alpha phase predicts illusory perception. Postdiction might actually be a means of compensating for the neural delays inherent in perceptual processes, so that the arrow of perceptual time matches the arrow of physical time.

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