Amplitude of the transient visual evoked potential (tVEP) as a function of achromatic and chromatic contrast: Contribution of different visual pathways

2008 ◽  
Vol 25 (3) ◽  
pp. 317-325 ◽  
Author(s):  
GIVAGO S. SOUZA ◽  
BRUNO D. GOMES ◽  
ELIZA MARIA C.B. LACERDA ◽  
CÉZAR A. SAITO ◽  
MANOEL DA SILVA FILHO ◽  
...  
Keyword(s):  
Contrast Sensitivity ◽  
Visual Pathways ◽  
Pattern Reversal ◽  
High Contrast ◽  
Chromatic Contrast ◽  
Low Contrast ◽  
Presentation Modes ◽  
Pattern Reversal Stimulation ◽  
Contrast Range ◽  
Visual Evoked

We investigated how the stimulation mode influences transient visual evoked potentials (tVEP) amplitude as a function of contrast of achromatic and isoluminant chromatic gratings. The chromatic stimulation probed only responses to the red-green axis. Visual stimuli were monocularly presented in a 5° diameter circle, achromatic and chromatic horizontal gratings, 1 Hz pattern reversal stimulation, and achromatic and chromatic gratings, 300 ms onset per 700 ms offset stimulation. For the achromatic pattern reversal stimulation, a double slope function describes how the P100 amplitude varied as a function of log contrast which had a limb at low-to-medium contrasts and another limb at high contrasts. For the achromatic onset/offset stimulation, C2 amplitude saturated at the highest contrast tested and a single straight line described how it changed along most of the contrast range. Both presentation modes for chromatic gratings resulted in amplitude versus log contrast relations which were well described by single straight lines along most of the contrast range. The results may be interpreted as if at 2 cpd, achromatic pattern reversal stimulation evoked the activity of at least two visual pathways with high and low contrast sensitivity, respectively, while achromatic onset/offset stimulation favored the activity of a pathway with high contrast sensitivity. The neural activity in the M pathway is the best candidate to be the high contrast mechanism detected with pattern reversal and pattern onset/offset VEPs. The activity of color opponent pathways such as the P and K pathways either combined or in isolation seems to be responsible for VEPs obtained with isoluminant chromatic gratings at both presentation modes. When the amplitudes of chromatic VEPs were plotted in the same contrast scale as used for achromatic VEPs, chromatic contrast thresholds had similar values to those of the achromatic mechanism with high contrast sensitivity.

Primary Presenile Dementia: The Use of the Visual Evoked Potential as a Diagnostic Indicator

1985 ◽  
Vol 147 (5) ◽  
pp. 532-539 ◽  
Author(s):  
Graham F. A. Harding ◽  
Christine E. Wright ◽  
Arnold Orwin
Keyword(s):  
Visual Evoked Potential ◽  
Evoked Potential ◽  
Cortical Atrophy ◽  
Control Group ◽  
Pattern Reversal ◽  
Presenile Dementia ◽  
The Difference ◽  
Pattern Reversal Stimulation ◽  
Diagnostic Indicator ◽  
Visual Evoked

The use of the flash and pattern reversal visual evoked potential (VEP) in the diagnosis of primary presenile dementia was investigated. The results from 20 patients with primary presenile dementia were compared with those from a control group of normals of equivalent age and from a control group of 20 patients with cortical atrophy but no dementia. Presenile dementia caused a slowing of the major positive (P2) component of the VEP to flash stimulation. However, the VEP to pattern reversal stimulation (P100) was of normal latency. The difference between these two latencies characterises this unusual combination of results and is found to be a more specific diagnostic indicator of primary presenile dementia than the EEG or CT scan.

scholarly journals Cortical Contrast Processing in Retinitis Pigmentosa: Evidence of PVEPs Spatial Functions

2020 ◽  
Vol 10 (4) ◽  
pp. 1010-1019
Author(s):  
Rafael Mancebo-Azor ◽  
José Antonio Sáez-Moreno ◽  
José Manuel Rodríguez-Ferrer
Keyword(s):  
Retinitis Pigmentosa ◽  
Evoked Potentials ◽  
Visual Evoked Potentials ◽  
Normal Subjects ◽  
Pattern Reversal ◽  
Check Size ◽  
Low Contrast ◽  
Control Subjects ◽  
The Right ◽  
Visual Evoked

Objective: To study the effect of check width size of the stimuli on the amplitude and latency of the P100 component of visual evoked potentials recorded in patients with retinitis pigmentosa (RP). Methods: Pattern reversal visual evoked potentials (PVEPs) were recorded in 16 RP patients and 20 visually normal subjects. Pattern reversal stimuli with five different check widths and 100% of contrast were projected in the right eye of both patients and control subjects. PVEPs induced by stimuli with 78%, 16%, and 6% of contrast were also recorded in 10 of the control subjects. Results: In RP patients, the amplitude of P100 was smaller than controls in all check sized used and the peak P100 amplitude was obtained with a larger check width than in controls. P100 was also delayed in RP patients in all check sizes studied. The P100 amplitude- and latency-check size functions of RP patients were like those found in control subjects with low contrast stimuli of 16% and 6%. Conclusion: The PVEPs spatial functions of RP patients show quantitative and qualitative changes, suggesting disease induced alteration in the neural processing of stimulus contrast.

Chromatic properties of neurons in macaque MT

1994 ◽  
Vol 11 (3) ◽  
pp. 455-466 ◽  
Author(s):  
Karl R. Gegenfurtner ◽  
Daniel C. Kiper ◽  
Jack M. H. Beusmans ◽  
Matteo Carandini ◽  
Qasim Zaidi ◽  
...  
Keyword(s):  
Contrast Sensitivity ◽  
Behavioral Contrast ◽  
Color Space ◽  
Contrast Threshold ◽  
High Contrast ◽  
Chromatic Contrast ◽  
Mt Neurons ◽  
Null Plane ◽  
Chromatic Properties ◽  
Almost All

AbstractWe have studied the responses of MT neurons to moving gratings, spatially modulated in luminance and chromaticity. Most MT neurons responded briskly and with high contrast sensitivity to targets whose luminance was modulated, with or without added chromatic contrast. When luminance modulation was removed and only chromatic stimulation was used, the responses of all MT neurons were attenuated. Most were completely unresponsive to stimulation with targets whose modulation fell within a “null” plane in color space; these null planes varied from neuron to neuron, but all lay close to the plane of constant photometric luminance. For about a third of the neurons, there was no color direction in which responses were completely abolished; almost all of these neurons had a definite minimum response for chromatic modulation near the isoluminant plane. MT neurons that responded to isoluminant targets did so inconsistently and with poor contrast sensitivity, so that only intensely modulated targets were effective. Whereas the best thresholds of MT neurons for luminance targets are close to behavioral contrast threshold, the thresholds for isoluminant targets lie considerably above behavioral contrast threshold. Therefore, although some MT neurons do give responses to isoluminant targets, they are unlikely to be the source of the chromatic motion signals revealed behaviorally.

Contrast Sensitivity as a Predictor of Complex Target Detection

1987 ◽  
Vol 31 (11) ◽  
pp. 1194-1197 ◽  
Author(s):  
David Shinar ◽  
Ehud Gilead
Keyword(s):  
Visual Acuity ◽  
Contrast Sensitivity ◽  
Target Detection ◽  
Undergraduate Students ◽  
Mountainous Terrain ◽  
High Contrast ◽  
Detection Time ◽  
Human Form ◽  
Low Contrast ◽  
Complex Target

A class of undergraduate students were screened for their visual acuity and contrast sensitivity on Ginsburg's charts. The subjects obtaining the highest and lowest contrast sensitivity scores were further tested on their complex target detection time. The complex targets consisted of a tank or a human form against a background of a mountainous terrain. The main finding was that target detection time for the high contrast sensitivity subjects was less than half of that of the low contrast sensitivity subjects. Differences in visual acuity between the two groups did not explain the differences in reaction time.

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