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.

Central Visual Persistence as Measured by the Redundant Target Effect

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 259-259 ◽  
Author(s):  
C A Marzi ◽  
G Nitro ◽  
M Prior
Keyword(s):  
Evoked Potential ◽  
Normal Subjects ◽  
Stimulus Onset ◽  
Visual Persistence ◽  
Single Stimulus ◽  
Redundant Target ◽  
Redundant Target Effect ◽  
Speed Of Response ◽  
Target Effect ◽  
Onset Asynchrony

We measured the duration of central visual persistence by testing normal subjects for the redundant target effect (RTE), ie the speeding up of reaction time to redundant visual stimuli in comparison to similar single stimuli. Brief LED-generated flashes were presented to normal subjects either singly or in a pair at peripheral visual field locations (5 or 30 deg along the horizontal meridian). Stimulus pairs could appear either in the same hemifield at different locations or in opposite hemifields with a stimulus onset asynchrony (SOA) ranging between 0 and 100 ms. The subject's task was to press a key as soon as possible following the appearance of either a single stimulus or of the first stimulus in a pair. We found a robust and consistent overall RTE with double stimuli yielding faster RTs than single stimuli for both intrafield and interfield presentations. The effect decreased significantly from 0 ms to 40 ms SOA and at longer SOAs the speed of response to stimulus pairs was indistinguishable from that to a single stimulus. We believe that the longest SOA compatible with a reliable RTE (40 ms) reflects the duration of central persistence. Evoked-potential evidence gathered in our laboratory suggests that the locus of such persistence may be the extrastriate visual cortex.

Semantic Processing of Foveally and Parafoveally Presented Words in a Lexical Decision Task

1992 ◽  
Vol 45 (2) ◽  
pp. 299-322 ◽  
Author(s):  
Luis J. Fuentes ◽  
Pío Tudela
Keyword(s):  
Visual Field ◽  
Lexical Decision ◽  
Lexical Decision Task ◽  
Semantic Processing ◽  
Stimulus Onset ◽  
Decision Task ◽  
Inhibitory Effects ◽  
Target Stimulus Onset Asynchrony ◽  
Onset Asynchrony ◽  
Prime Target

Using a lexical decision task in which two primes appeared simultaneously in the visual field for 150 msec followed by a target word, two experiments examined semantic priming from attended and unattended primes as a function of both the separation between the primes in the visual field and the prime-target stimulus-onset asynchrony (SOA). In the first experiment significant priming effects were found for both the attended and unattended prime words, though the effect was much greater for the attended words. In addition, and also for both attention conditions, priming showed a tendency to increase with increasing eccentricity (2.3°, 3.3°, and 4.3°) between the prime words in the visual field at the long (550 and 850 msec) but not at the short (250 msec) prime-target SOA. In the second experiment the prime stimuli were either two words (W-W) or one word and five Xs (W-X). We manipulated the degree of eccentricity (2° and 3.6°) between the prime stimuli and used a prime-target SOA of 850 msec. Again significant priming was found for both the attended and unattended words but only the W-W condition showed a decrement in priming as a function of the separation between the primes; this decrement came to produce negative priming for the unattended word at the narrow (2°) separation. These results are discussed in relation to the semantic processing of parafoveal words and the inhibitory effects of focused attention.

Parallel but Temporally Displaced Visual Half-Field Metacontrast Functions

1974 ◽  
Vol 26 (2) ◽  
pp. 258-265 ◽  
Author(s):  
Walter F. McKeever ◽  
Max Suberi
Keyword(s):  
Visual Field ◽  
Stimulus Onset Asynchrony ◽  
Left Visual Field ◽  
Right Hemisphere ◽  
Stimulus Onset ◽  
Right Visual Field ◽  
Field Function ◽  
Processing Delay ◽  
The Right ◽  
Onset Asynchrony

Using a classic letter-ring metacontrast paradigm, left and right visual field meta-contrast functions were separately determined. The parallel U-shaped recognition functions for both half-fields were found to interact differentially with stimulus onset asynchrony, the left visual field function being displaced by 13 ms toward longer test stimulus-masking stimulus separations. This result was consistent with the hypothesis of longer processing time requirements for verbal stimuli delivered to the right than to the left hemisphere. This indicates that the neural locus (loci) responsible for left visual field verbal processing delay is (are) capable of mediating metacontrast phenomena. It was tentatively concluded that a relative processing delay within the right hemisphere underlies the differing visual half-field metacontrast interaction with stimulus onset asynchrony.

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.

Visual Integration during Saccadic and Pursuit Eye Movements: The Importance of Spatial Framework

1993 ◽  
Vol 77 (3_suppl) ◽  
pp. 1219-1234
Author(s):  
Hiroshi Watanabe ◽  
Naoto Suzuki
Keyword(s):  
Eye Movements ◽  
Visual Field ◽  
Stimulus Onset Asynchrony ◽  
Saccadic Eye Movements ◽  
Stimulus Onset ◽  
Visual Persistence ◽  
Visual Integration ◽  
Pursuit Eye Movements ◽  
Onset Asynchrony ◽  
Accuracy Rates

Three experiments were conducted to clarify the function of spatiotopic and retinotopic visual persistence during pursuit and saccadic eye movements. Exps. 1 and 2 both showed spatiotopic visual integration for both types of eye movements, although shorter stimulus onset asynchrony (SOA) was set in Exp. 2. Exp. 3 was conducted with special attention to the absence of target stimuli when masking stimuli were presented. Although duration of target stimuli and stimulus onset asynchrony in Exp. 3 were longer than those in the first two experiments, analysis contrastively showed retinotopic visual integration during saccades and very low accuracy rates under all conditions during pursuit eye movements. The above indicates that the basis for the functional switching between spatiotopic and retinotopic visual integration may have been the existence of a visual framework for visual integration or the synchronous existence of target and masking stimuli in the visual field, not the duration of target stimuli and stimulus onset asynchrony. Such integration of the reference point may possibly be processed through a higher mechanism and not at the retinal level.

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.

scholarly journals Integrated electrophysiological evaluation in early normal-tension glaucoma

2016 ◽  
Vol 1 (2) ◽  
pp. 79-88
Author(s):  
Dario Messenio ◽  
Giuseppe Marano ◽  
Elia Biganzoli
Keyword(s):  
Optic Nerve ◽  
Visual Field ◽  
Evoked Potentials ◽  
Visual Evoked Potentials ◽  
Optic Nerve Head ◽  
Pattern Electroretinogram ◽  
Normal Subjects ◽  
Visual Field Defects ◽  
Control Group ◽  
Visual Evoked

Purpose: To evaluate the variations of intraocular pressure (IOP), morphometric optic nerve head characteristic, perimetric indices and electrophysiological parameters (pattern electroretinogram and visual evoked potentials) before and after topical IOP lowering in patients with early normal-tension glaucoma.Methods: we evaluated 38 eyes of 20 patients with IOP < 21 mmHg, initial glaucomatous optic neuropathy (valued with HRT: retinal nerve fiber layer thickness (RNFL) and linear cup/disk ratio (linear C/D ratio)), minimal visual field defects (Octopus 101: G2 program), best correct visual acuity more than 15/20 and pathological electrophysiological parameters (valued with pattern electroretinogram (PERG) and visual evoked potentials (VEPs)), free of systemic or other ocular diseases. All parameters were evaluated at the beginning of the study (T0) and after 12 months of therapy (T12). A randomized normal control group (27 eyes of 14 subjects) with apparent larger disc cupping underwent all exams at initial of study (T0) and after 12 months (T12).Results: Among electrophysiological parameters, at the beginning of the study NTG P100 VEPs latency is slightly increased and P100 amplitude is reduced compared to normal subjects. There are not significant variations after 12 months. P50 PERG latency in NTG is quite similar respect normal and do not modify after therapy. P50N95 complex PERG amplitude in NTG is reduced compared to normal subjects and slightly increases after 12 months (1.8 vs 1.5 ; 2.4 vs 1.9 micronvolts, with different checkboard spatial frequency). Cortical retinal time (CRT) is slightly delayed in NTG and does not modify. Among visual field indices, MD and CLV is slightly higher in NTG and do not significantly modify after therapy. Among morphometric optic nerve head characteristics, linear C/D and RNFL thickness are quite similar in NTG and do not modify. IOP is quite similar between NTG and control group and modifies in NTG after therapy.Conclusion: In a viewpoint of an integrated diagnostic, electrophysiological tests (VEPs and PERG) could provide a more sensitive measure of retinal ganglion cell integrity and help to distinguish between early normal-pressure glaucoma patients with no or minimal visual field alterations and normal subjects with apparent larger disc cupping.

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