scholarly journals Distinct Patterns of P1 and C2 VEP Potentiation and Attenuation in Visual Snow: A Case Report

2021 ◽  
Vol 12 ◽  
Author(s):  
Alison M. Harris
Keyword(s):  
Visual Processing ◽  
Stimulus Presentation ◽  
Stimulus Onset ◽  
Pattern Reversal ◽  
Current Dipole ◽  
Opposite Pattern ◽  
Cortical Responses ◽  
Pattern Onset Vep ◽  
Foveal Stimulation

Visual snow syndrome, characterized by persistent flickering dots throughout the visual field, has been hypothesized to arise from abnormal neuronal responsiveness in visual processing regions. Previous research has reported a lack of typical VEP habituation to repeated stimulus presentation in patients with visual snow. Yet these studies generally used pattern-reversal paradigms, which are suboptimal for measuring cortical responses to the onset of foveal stimulation. Instead, these responses are better indexed by the C2, a pattern-onset VEP peaking 100–120 ms after stimulus onset. In this case study, we analyzed the C2 and its adaptation profile in data previously collected from a single patient with visual snow using a “double-pulse” presentation paradigm. In controls, shorter intervals between stimulus pairs were associated with greater attenuation of the C2 VEP, with recovery from adaptation at longer stimulus onset asynchronies (SOAs). However, the visual snow patient showed the opposite pattern, with reduced C2 amplitude at longer SOAs despite distinct C2 peaks at the shortest SOAs. These results stand in contrast not only to the pattern of C2 VEP attenuation in controls, but also to a lack of adaptation previously reported for the pattern-onset P1 VEP in this patient. Exploratory source localization using equivalent current dipole fitting further suggested that P1 and C2 VEPs in the visual snow patient arose from distinct sources in extrastriate visual cortex. While preliminary, these results support differential patterns of VEP attenuation and potentiation within the same individual, potentially pointing toward multiple mechanisms of abnormal neuronal responsiveness in visual snow syndrome.

Non-Linear Interactions in Cortical Responses to Bilateral vs Unilateral Visual Field Stimulation

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 62-62
Author(s):  
S P Ahlfors ◽  
J J Foxe ◽  
R J Ilmoniemi ◽  
G V Simpson
Keyword(s):  
Visual Field ◽  
Evoked Potentials ◽  
Normal Subjects ◽  
Stimulus Onset ◽  
Current Dipole ◽  
Field Patterns ◽  
Cortical Responses ◽  
Bilateral Case ◽  
Multichannel Recordings ◽  
Onset Asynchrony

Stimuli in different parts of the visual field can be perceived as independent entities and as conjoined wholes. It is of interest to determine whether there are cortical representations of the left and right hemifields which remain as independent entities when both hemifields are stimulated simultaneously and/or whether they interact to form a conjoined representation. We examined whether cortical processing of visual stimuli depends on whether they occur in isolation in one hemifield (unilaterally) or simultaneously in both hemifields (bilaterally). Visual evoked potentials of six normal subjects were recorded from 128 scalp sites. Wedge-shaped chequerboard stimuli, extending 1 – 4 deg eccentricity, were presented to quadrants of the visual field. Stimulus duration was 250 ms; the stimulus onset asynchrony was random, 500 – 750 ms. The evoked potentials revealed multiple peaks of activity with different surface topography. Prominent deflections occurred around 80, 120 – 180, and 230 ms. The response to bilateral stimuli was compared with the sum of the responses to unilateral stimuli. On the basis of the multichannel recordings, nonlinear interactions were characterised as either (a) modulations (same generators, but different amplitude) or (b) interactions originating from different generators. Modulation occurred at 230 ms, the response being suppressed for the bilateral case. At 120 – 180 ms, the field patterns suggested that at least some of the sources of the interaction effect are different from the source of the bilateral response. Underlying generators of the evoked responses and the interaction effects were further explored with the use of an equivalent current dipole model.

scholarly journals Oscillatory Characteristics of Nociceptive Responses in the SII Cortex

2008 ◽  
Vol 35 (5) ◽  
pp. 630-637 ◽  
Author(s):  
Fu-Jung Hsiao ◽  
Wei-Ta Chen ◽  
Kwong-Kum Liao ◽  
Zin-An Wu ◽  
Low-Tone Ho ◽  
...  
Keyword(s):  
Statistical Power ◽  
Stimulus Onset ◽  
Pain Level ◽  
Thulium Laser ◽  
Current Dipole ◽  
Left Hand ◽  
Power Difference ◽  
Nociceptive Responses ◽  
Cortical Responses ◽  
Pain Stimuli

Objective:This study is aimed to explore the frequency characteristics of pain-evoked neuromagnetic responses in the secondary somatosensory (SII) cortices.Methods:Thulium-laser nociceptive stimuli to the left hand dorsum of 10 right-handed healthy adults. The pain stimuli were rated as mild, moderate, and severe levels according to subjects' reports on a 10-point visual analog scale. We analyzed their cortical responses with wavelet-based frequency analyses and equivalent current dipole (ECD) modeling.Results:For each pain level, we found an increase of theta (4-8 Hz) and alpha (8-13 Hz) power in bilateral SII areas at 180-210 ms after stimulus onset. The power was larger for the moderate than for the mild pain level (p < 0.05), but there was no statistical power difference of these oscillations between moderate and severe pain stimulus conditions (p = 0.7). Within the SII area, we did not observe particular difference in theta and alpha ECD locations between varying pain level conditions.Conclusions:The 4-13 Hz activities, peaking from 180 to 210 ms, are oscillatory correlates of SII activation in response to nociceptive stimulation, but their power may code the magnitude of pain stimuli only up to moderate level, as rated subjectively. This measure could be potentially used to evaluate SII activation in further pain studies.

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.

scholarly journals The Rapid Extraction of Gist—Early Neural Correlates of High-level Visual Processing

2012 ◽  
Vol 24 (2) ◽  
pp. 521-529 ◽  
Author(s):  
Frank Oppermann ◽  
Uwe Hassler ◽  
Jörg D. Jescheniak ◽  
Thomas Gruber
Keyword(s):  
Visual Processing ◽  
Time Course ◽  
Occipital Cortex ◽  
Stimulus Onset ◽  
Gamma Band ◽  
Oscillatory Activity ◽  
Rapid Extraction ◽  
The Right ◽  
High Level ◽  
Individual Objects

The human cognitive system is highly efficient in extracting information from our visual environment. This efficiency is based on acquired knowledge that guides our attention toward relevant events and promotes the recognition of individual objects as they appear in visual scenes. The experience-based representation of such knowledge contains not only information about the individual objects but also about relations between them, such as the typical context in which individual objects co-occur. The present EEG study aimed at exploring the availability of such relational knowledge in the time course of visual scene processing, using oscillatory evoked gamma-band responses as a neural correlate for a currently activated cortical stimulus representation. Participants decided whether two simultaneously presented objects were conceptually coherent (e.g., mouse–cheese) or not (e.g., crown–mushroom). We obtained increased evoked gamma-band responses for coherent scenes compared with incoherent scenes beginning as early as 70 msec after stimulus onset within a distributed cortical network, including the right temporal, the right frontal, and the bilateral occipital cortex. This finding provides empirical evidence for the functional importance of evoked oscillatory activity in high-level vision beyond the visual cortex and, thus, gives new insights into the functional relevance of neuronal interactions. It also indicates the very early availability of experience-based knowledge that might be regarded as a fundamental mechanism for the rapid extraction of the gist of a scene.

Context-Dependent Modulation of Early Visual Cortical Responses to Numerical and Nonnumerical Magnitudes

2021 ◽  
pp. 1-12
Author(s):  
Joonkoo Park ◽  
Sonia Godbole ◽  
Marty G. Woldorff ◽  
Elizabeth M. Brannon
Keyword(s):  
Visual Processing ◽  
Context Dependency ◽  
Numerical Magnitude ◽  
Continuous Variables ◽  
Processing Stream ◽  
Cortical Responses ◽  
Early Visual Cortex ◽  
Context Dependent ◽  
Visual Cortical ◽  
The Brain

Abstract Whether and how the brain encodes discrete numerical magnitude differently from continuous nonnumerical magnitude is hotly debated. In a previous set of studies, we orthogonally varied numerical (numerosity) and nonnumerical (size and spacing) dimensions of dot arrays and demonstrated a strong modulation of early visual evoked potentials (VEPs) by numerosity and not by nonnumerical dimensions. Although very little is known about the brain's response to systematic changes in continuous dimensions of a dot array, some authors intuit that the visual processing stream must be more sensitive to continuous magnitude information than to numerosity. To address this possibility, we measured VEPs of participants viewing dot arrays that changed exclusively in one nonnumerical magnitude dimension at a time (size or spacing) while holding numerosity constant and compared this to a condition where numerosity was changed while holding size and spacing constant. We found reliable but small neural sensitivity to exclusive changes in size and spacing; however, changing numerosity elicited a much more robust modulation of the VEPs. Together with previous work, these findings suggest that sensitivity to magnitude dimensions in early visual cortex is context dependent: The brain is moderately sensitive to changes in size and spacing when numerosity is held constant, but sensitivity to these continuous variables diminishes to a negligible level when numerosity is allowed to vary at the same time. Neurophysiological explanations for the encoding and context dependency of numerical and nonnumerical magnitudes are proposed within the framework of neuronal normalization.

Temporal-Order Judgment and Reaction Time to Stimuli of Different Rise Times

Perception ◽  
1993 ◽  
Vol 22 (8) ◽  
pp. 963-970 ◽  
Author(s):  
Piotr Jaśkowski
Keyword(s):  
Reaction Time ◽  
Simple Reaction Time ◽  
Temporal Order ◽  
Temporal Order Judgment ◽  
Stimulus Presentation ◽  
Stimulus Onset ◽  
Simple Reaction ◽  
Point Of Subjective Simultaneity ◽  
Subjective Simultaneity ◽  
The Subject

Point of subjective simultaneity and simple reaction time were compared for stimuli with different rise times. It was found that these measures behave differently. To explain the result it is suggested that in the case of temporal-order judgment the subject takes into account not only the stimulus onset but also other events connected with stimulus presentation.

scholarly journals The role of action intentionality and effector in the subjective expansion of temporal duration after saccadic eye movements

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
David Melcher ◽  
Devpriya Kumar ◽  
Narayanan Srinivasan
Keyword(s):  
Eye Movements ◽  
Visual Processing ◽  
Saccadic Eye Movements ◽  
Intentional Binding ◽  
Opposite Pattern ◽  
Motor Action ◽  
Saccade Onset ◽  
Backward Shift ◽  
The Moment

Abstract Visual perception is based on periods of stable fixation separated by saccadic eye movements. Although naive perception seems stable (in space) and continuous (in time), laboratory studies have demonstrated that events presented around the time of saccades are misperceived spatially and temporally. Saccadic chronostasis, the “stopped clock illusion”, represents one such temporal distortion in which the movement of the clock hand after the saccade is perceived as lasting longer than usual. Multiple explanations for chronostasis have been proposed including action-backdating, temporal binding of the action towards the moment of its effect (“intentional binding”) and post-saccadic temporal dilation. The current study aimed to resolve this debate by using different types of action (keypress vs saccade) and varying the intentionality of the action. We measured both perceived onset of the motor action and perceived onset of an auditory tone presented at different delays after the keypress/saccade. The results showed intentional binding for the keypress action, with perceived motor onset shifted forwards in time and the time of the tone shifted backwards. Saccades resulted in the opposite pattern, showing temporal expansion rather than compression, especially with cued saccades. The temporal illusion was modulated by intentionality of the movement. Our findings suggest that saccadic chronostasis is not solely dependent on a backward shift in perceived saccade onset, but instead reflects a temporal dilation. This percept of an effectively “longer” period at the beginning of a new fixation may reflect the pattern of suppressed, and then enhanced, visual processing around the time of saccades.

Rethinking patient–provider care through visual communication

2020 ◽  
pp. 147035722091560
Author(s):  
Stacy Elko ◽  
John A Velez ◽  
Melinda Corwin ◽  
Justin Robert Keene
Keyword(s):  
Health Care Providers ◽  
Visual Processing ◽  
Visual Communication ◽  
Visual Design ◽  
Interactive Narrative ◽  
Care Providers ◽  
Narrative Intervention ◽  
Life Issues ◽  
Visual Design Principles

The case study presented in this article developed an improved intervention for visually communicating with persons diagnosed with a communication disorder known as aphasia. The Visual Interactive Narrative Intervention (VINI) assists health-care providers in educating post-stroke persons with aphasia (PWA) about their stroke, symptoms, rehabilitation options, and quality of life issues. Visual communication is under-utilized to convey health information to PWA despite its ability to capitalize on their intact cognitive and visual processing. The current Reflections on Practice summarizes visual guidelines from previous research, discusses visual design principles to achieve these guidelines, and presents a case study of creating visual stimuli for PWA based on these considerations and initial pilot testing with PWA. The case study demonstrates the creative process, the visual design considerations, and the interdisciplinary effort (i.e. health professionals, artists, and communication scholars) necessary for visually communicating with PWA.

scholarly journals Differential Influence of Attention on Gaze and Head Movements

2009 ◽  
Vol 101 (1) ◽  
pp. 198-206 ◽  
Author(s):  
Aarlenne Z. Khan ◽  
Gunnar Blohm ◽  
Robert M. McPeek ◽  
Philippe Lefèvre
Keyword(s):  
Reaction Times ◽  
Stimulus Onset ◽  
Head Movements ◽  
Neck Muscle ◽  
Gaze Shifts ◽  
Opposite Pattern ◽  
Saccade Onset ◽  
Highly Correlated ◽  
Onset Asynchrony ◽  
Electromyographic Signals

A salient peripheral cue can capture attention, influencing subsequent responses to a target. Attentional cueing effects have been studied for head-restrained saccades; however, under natural conditions, the head contributes to gaze shifts. We asked whether attention influences head movements in combined eye–head gaze shifts and, if so, whether this influence is different for the eye and head components. Subjects made combined eye–head gaze shifts to horizontal visual targets. Prior to target onset, a behaviorally irrelevant cue was flashed at the same (congruent) or opposite (incongruent) location at various stimulus-onset asynchrony (SOA) times. We measured eye and head movements and neck muscle electromyographic signals. Reaction times for the eye and head were highly correlated; both showed significantly shorter latencies (attentional facilitation) for congruent compared with incongruent cues at the two shortest SOAs and the opposite pattern (inhibition of return) at the longer SOAs, consistent with attentional modulation of a common eye–head gaze drive. Interestingly, we also found that the head latency relative to saccade onset was significantly shorter for congruent than that for incongruent cues. This suggests an effect of attention on the head separate from that on the eyes.

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