Human VEP contrast modulation sensitivity: separation of magno- and parvocellular components

Investigation of the bio-stimulation of children's reading interest by chromatic pattern visual evoked potential

PURPOSE

The characteristics of children's reading interest, stimulated by the visual evoked potentials of colour graphics in children's picture books, were tested to explore their normal reference value. The characteristics of chromatic pattern visual evoked potential (CP-VEP) can be harnessed by our methodology and may be applied to the visual screening of children in clinical ophthalmology.

METHODS

The PR-650 spectral colour metre can strictly control factors, such as brightness and colour retention, based on colour contrast. This is performed in order to reduce the brightness contrast method. In our paper, we set up three kinds of visual stimulation conditions and performed CP-VEP inspections of the eye, based on 64 cases (128 eyes) of normal children (32 males and 32 females). Using CP-VEP detection, the latency and amplitude of the P100 wave were recorded and the waveforms of each group, under different spectral modes were compared. Art therapy combined with children's colour physiology and psychology will be more skilfully practiced in clinical practice.

RESULTS

There was no significant difference in the amplitude and peak time of visual evoked potential (VEP) waveforms between the left and right eyes of the children using the three stimuli, indicating that the visual function and visual conduction pathway of children can vary. There was no significant difference in the latency and amplitude of the NPN complex wave. Note that the P1 wave of the right and left eyes of normal children is not statistically different (P > 0.05). We also found that there is insignificant difference in the visual impact of the colours for both male and female children in terms of reading interest, and red is a more stimulating colour for both sexes.

CONCLUSION

Our study can provide normal reference value and methodological reference for clinical visual acuity detection in children. Combined with the visual characteristics of children, this paper selects the visual impact created by the colour of picture books and combines it with medical treatment. Make the whole test cover the scope of ophthalmology clinical more comprehensive.

Evaluation of optic neuropathy in multiple sclerosis using low-contrast visual evoked potentials

BACKGROUND

Contrast acuity (identification of low-contrast letters on a white background) is frequently reduced in patients with demyelinating optic neuropathy associated with multiple sclerosis (MS), even when high-contrast (Snellen) visual acuity is normal. Since visual evoked potentials (VEPs) induced with high-contrast pattern-reversal stimuli are typically increased in latency in demyelinating optic neuropathy, we asked if VEPs induced with low-contrast stimuli would be more prolonged and thus helpful in identifying demyelinating optic neuropathy in MS.

METHODS

We studied 15 patients with clinically definite MS and 15 age-matched normal controls. All subjects underwent a neuro-ophthalmologic assessment, including measurement of high-contrast visual acuity and low-contrast acuities with 25%, 10%, 5%, 2.5%, and 1.25% contrast Sloan charts. In patients with MS, peripapillary retinal nerve fiber layer (RNFL) thickness was determined using optical coherence tomography. Monocular VEPs were induced using pattern-reversal checkerboard stimuli with 100% and 10% contrast between checks, at 5 spatial frequencies (8-130 minutes of arc).

RESULTS

VEP latencies were significantly increased in response to low- compared with high-contrast stimuli in both groups. VEP latencies were significantly greater in patients with MS than controls for both high- and low-contrast stimuli. VEP latencies correlated with high- and low-contrast visual acuities and RNFL thickness. VEPs were less likely to be induced with low- than with high-contrast stimuli in eyes with severe residual visual loss.

CONCLUSIONS

Visual evoked potentials obtained in patients with multiple sclerosis using low-contrast stimuli are increased in latency or absent when compared with those obtained using high-contrast stimuli and, thus, may prove to be helpful in identifying demyelinating optic neuropathy.

Pattern visual evoked potentials in malingering

OBJECTIVES

We previously developed a new method for estimating objective visual acuity by means of pattern visual evoked potentials (PVEP). In this study, this method was applied to the diagnosis of malingering.

MATERIALS AND METHODS

Six patients ranging in age from 40 to 54 years (mean 47 years) with suspected malingering were evaluated by means of the visual evoked potential test, optokinetic nystagmus (OKN) inhibition test, and the visual field test. In the PVEP study, the stimulus consisted of black and white checkerboards (39', 26', 15', and 9') with a visual angle of 8 degrees, contrast level of 15%, and a frequency of 0.7 Hz. One hundred PVEP responses were averaged per session.

RESULTS

Routine ophthalmic examinations were normal in all patients. Five patients had a tubularly constricted visual field, and the remaining patient had a normal visual field. The objective visual acuities of the six patients estimated from PVEP were better than their subjective visual acuities estimated with Landolt rings.

CONCLUSIONS

Among a variety of psychophysical and electrophysiologic ancillary tests, we consider our PVEP method a useful method for objectively determining visual acuity in a patient with signs of ocular malingering.

The effect of spatial frequency on chromatic and achromatic steady-state visual evoked potentials

OBJECTIVE

Little is known about the physiological properties of the major components of steady-state visual evoked potentials (VEPs). Based on the hypothesis that isoluminant color and high contrast pattern differentially activate the parvo- and magnocellular pathways, we studied difference in spatial frequency function between chromatic and achromatic VEPs to sinusoidal gratings.

METHODS

Steady-state VEPs to isoluminant chromatic (red-green) and high contrast (90%) achromatic (black-white) sinusoidal gratings with nine spatial frequencies (0.5 to 8.0 cycles/degrees (cpd)) at 4 Hz (8 reversals/s) were recorded in 13 normal subjects. VEPs were Fourier analyzed to obtain phase and amplitude of the second (2F) and fourth (4F) harmonic responses.

RESULTS

The 2F amplitude of chromatic VEPs decreased above 4.0 cpd in a low-pass function while that of achromatic VEPs showed a band-pass function with a peak at 4.0 cpd. The 4F amplitude of chromatic VEPs was not affected significantly by spatial frequency whereas that of achromatic VEPs exhibited a high-pass function. The phases of 2F and 4F showed a non-monotonic function of spatial frequency in both chromatic and achromatic stimuli with peaks at middle spatial frequencies.

CONCLUSION

Chromatic and achromatic visual stimuli differently affected 2F and 4F components, which thus suggests that 2F and 4F components are generated from different neuronal subgroups largely in the parvocellular pathway.

Effects of pattern, spatial frequency, number, and rate of stimulus presentation on the accuracy of detection

Brief trains of pulsed stimuli were used to assess whether magnocellular or parvocellular visual pathways could be differentiated perceptually. Trains of either one to four sine-wave, square-wave, or checkerboard gratings were presented at three temporal and two spatial frequencies to six observers. The task of the observer was to report the perceived number of stimuli (gratings) in a train. The difference between actual number and perceived number of gratings was recorded as an error score. It was found that neither the pattern nor the spatial frequency of the gratings significantly affected perceptual accuracy. On the other hand, the number of gratings in a train and the interstimulus interval between gratings produced significant differences. Perceptual accuracy was greater when lower numbers of gratings in a train were presented with longer interstimulus intervals. The observers typically reported fewer stimuli than were presented. The source of the discrepancy is discussed in terms of a light adaptive process initiated in the retina.

Chemosensory event-related potentials in response to trigeminal and olfactory stimulation in idiopathic Parkinson's disease

Decrease of olfactory function in patients with Parkinson's disease (PD) has been reported by several authors. The current study investigated olfaction in PD patients using olfactory event-related potentials (OERPs) as an electrophysiologic correlate of olfactory function in combination with psychophysical testing. A specific focus was the influence of antiparkinsonian drugs. We investigated PD patients treated with antiparkinsonian drugs (n = 13) and PD patients who received no pharmacologic treatment (n = 18). They were compared to age- and sex-matched control subjects (n = 38). To obtain OERPs, stimulants were chosen to stimulate specifically the olfactory nerve (2.1 ppm vanillin, 0.8 ppm H2S). In addition, chemosomatosensory event-related potentials were recorded after trigeminal stimulation with 52% v/v CO2. Moreover, the subjects' ability to identify and to discriminate odorants was tested by means of a "squeeze bottle" technique. The study yielded the following major results: (1) Odor identification was impaired in PD patients. It was not influenced by treatment with antiparkinsonian drugs. (2) The OERP latencies were prolonged in both PD patients taking and not taking antiparkinsonian drugs; however, this effect was more pronounced in PD patients taking antiparkinsonian drugs. (3) The intranasal chemosensory trigeminal system seemingly was neither affected by the neuronal degeneration seen in PD nor by treatment with antiparkinsonian drugs.

M and P components of the VEP and their visual field distribution

To study components related to parallel processing of information across the visual field, multi-focal pattern reversal visual evoked potentials (VEPs) were recorded using binary m-sequences. Contrast, chromatic, spatial and temporal characteristics of the stimuli were varied in order to favor contributions from either M or P pathways. Responses were decomposed into two additive components whose behavior was consistent with that of M and P mechanisms. The results suggest that contributions to the VEP from the M pathway precede those from the P pathway, and that the ratio of P/M contributions decreases with eccentricity.

The effects of luminance and chromatic background flicker on the human visual evoked potential

Previous studies report that background luminance flicker, which is asynchronous with signal averaging, reduces the amplitude and increases the latency of the pattern-onset visual evoked potential (VEP). This effect has been attributed to saturation of the magnocellular (m-) pathway by the flicker stimulus. In the current study, we evaluate this hypothesis and further characterize this effect. We found that flicker had similar effects on the pattern-onset and pattern-reversal VEP, suggesting that the reversal and onset responses have similar generators. Chromatic flicker decreased latency of the chromatic VEP whereas luminance flicker increased peak latency to luminance targets. This result indicates that luminance flicker saturates a rapidly conducting m-pathway whereas chromatic flicker saturates a more slowly conducting parvocellular (p-) pathway. Finally, evoked potentials to chromatic and luminance stimuli were recorded from 34 electrodes over the scalp in the presence of static and asynchronously modulated backgrounds. An equivalent dipole model was used to assess occipital, parietal, and temporal lobe components of the surface response topography. Results showed that chromatic flicker reduced activity to a greater extent in the ventral visual pathway whereas luminance flicker reduced activity to a greater extent in the dorsal visual pathway to parietal lobe. We conclude that the VEP to isoluminant color and luminance stimuli contains both m- and p-pathway components. Asynchronous flicker can be used to selectively reduce the contribution of these pathways to the surface recorded VEP. Our results provide evidence of parallel pathways in the human visual system, with a dorsal luminance channel projecting predominantly to the posterior parietal lobe and a ventral color channel projecting predominantly to inferior temporal lobe.

Human VEPs to isoluminant chromatic and achromatic sinusoidal gratings: separation of parvocellular components

To extract the responses specific to the parvocellular system (color vision and form perception) in humans, visual evoked potentials (VEPs) in response to the onset of isoluminant chromatic (red-green) and achromatic (black-white) sinusoidal gratings were recorded in 15 young adults. Chromatic stimulation evoked a characteristic negative wave (N1) with peak latencies around 120 msec. The amplitude resembled an inverse U-shaped function against the spatial frequency with a peak at 2 c/deg. In contrast, VEPs to achromatic gratings showed different spatial frequency characteristics with a peak at 5.3 c/deg. With variations in the luminous intensity ratio between the red and green gratings, N1 was seen to respond maximally to isoluminant stimulation. These results indicate that the combined use of isoluminant chromatic and achromatic patterns could stimulate the parvocellular system selectively in humans.

Visual evoked potentials generator model derived from different spatial frequency stimuli of visual field regions and magnetic resonance imaging coordinates of V1, V2, V3 areas in man

Visual evoked potentials (VEPs) to pattern reversal vertical bar stimuli were recorded from 24 scalp derivations (including zygomatic and inion) referenced to digitally linked earlobes in 50 controls. 1, 2 and 4 cpd patterns were presented as full field (FF) stimuli, on Upper Hemifields (UHF) and Lower Hemifields (LHF), upper and lower quadrants and with the occlusion of central and peripheral UHF and LHF. VEPs to octant stimuli were also recorded with 2 cpd patterns. N1, P1 and N2 components were recorded from posterior and inion derivations with FF stimuli, from posterior derivations with LHF stimuli, only from inion leads with UHF stimuli, from derivations ipsilateral to stimuli with quadrants and octants, and consistently from midline derivations only with lower quadrants. Polarity inverted sequences (iN1-iP1-iN2) were recorded from the other scalp derivations, with similar latency and spatial frequency sensitivity as N1-P1-N2. Single Equivalent Dipole (ED) calculations were performed on N1 and P1 recorded in the different stimulus conditions. Our findings contradict previous hypotheses on VEP generators and contradict the predictions of VEPs polarity and distribution based on the "cruciform model" of VEPs generators. In order to explain the distribution of VEPs to upper and lower half fields and to quadrant and octants, we propose a model based on the position of the medial and occipito-polar surface of visual cortex in man.

Parvocellular and magnocellular contributions to visual evoked potentials in humans: stimulation with chromatic and achromatic gratings and apparent motion

Psychophysical evidence suggests that two major parallel pathways, the parvocellular (P) and the magnocellular (M) pathways, exist in humans. We herein report that responses specific to the P and M systems can be recorded in human visual evoked potentials (VEPs) by using the appropriate stimuli. The onset of isoluminant chromatic (red-green) and high contrast achromatic sinusoidal gratings were used for stimulating the P-system. A chromatic stimulation evoked a characteristic negative wave (N1) with peak latencies around 120 msec. The amplitude showed an inverse U-shaped function as a function of spatial frequency with a peak at 2 c/deg. In contrast, VEPs to achromatic (black-white) gratings showed different spatial frequency characteristics with a peak at 5.3 c/deg. By varying the luminous intensity ratio between the red and green gratings, N1 was found to reach a maximum during isoluminant stimulation. An apparent motion display was used for stimulating the M-system. The speed of alternation (i.e., the interstimulus interval (ISI)) was varied to record both the transient and steady-state VEPs. Transient VEPs showed triphasic waves with the major positive peak (P1) at around 120 ms. Steady-state VEPs were quasi-sinusoidal waveforms, depending on the ISI, and were quite stable across all subjects. There was a also high correlation between the motion threshold and the VEP amplitude. The above observations indicate that characteristic potentials may distinguish between these two parallel visual systems in humans. Thus, the combined use of isoluminant color and high contrast achromatic gratings and an apparent motion display is considered to be useful for evaluating both systems electrophysiologically.

Source model and scalp topography of pattern reversal visual evoked potentials to altitudinal stimuli suggest that infoldings of calcarine fissure are not part of VEP generators

Visual evoked potentials (VEPs) to pattern reversal vertical bar stimuli were recorded from 19 scalp, 2 zygomatic and 3 inion derivations referenced to digitally linked earlobes in 50 controls. 1, 2 and 4 cycles per degree (cpd) patterns were presented as full field (FF) stimuli, on upper and lower hemifields (UHF-LHF), upper and lower quadrants and with the occlusion of central and peripheral UHF and LHF. VEPs to octant stimuli were also recorded with 2 cpd patterns. N1, P1 and N2 components were recorded from posterior and inion derivations with FF stimuli, from posterior derivations with LHF stimuli, only from inion leads with UHF stimuli, from derivations ipsilateral to stimuli with quadrants and octants, and from midline derivations only with lower quadrants. Polarity inverted sequences (iP1-iN1-iP2) were recorded from the other scalp derivations, with similar latency and spatial frequency sensitivity as N1-P1-N2. The orientation of Equivalent Dipoles (ED) was orthogonal with surface coordinates of mesial and occipito-polar calcarine cortex, measured on Magnetic Resonance Imaging. A model of VEP generators is proposed, suggesting that the VEP sequence is elicited only in mesial and occipito-polar surfaces of calcarine cortex.

Visual thresholds to low-contrast pattern displacement, color contrast, and luminance contrast stimuli in Parkinson's disease

We used the computerized Moorfield Vision System to demonstrate specific increases in various perceptual visual thresholds in idiopathic Parkinson's syndrome. Fifteen patients were compared to 13 age-matched normals. Motion detection was impaired maximally (2 p < 0.01 and better in two-tailed t test) at luminance contrasts of 3-7%. Stimulus was an achromatic vertical 4 cycles/degrees sine wave grating subtending 3 degrees x 2 degrees, centered 5 degrees in the nasal field and oscillating at 5 Hz. In addition, stationary color and luminance contrast thresholds were tested with flashed display of 5 degrees x 6 degrees random letters, which were presented for 200 ms (color) and 50 ms (achromatic). Color discrimination was impaired in the tritan axis only (2 p < 0.05 in two-tailed t test). All achromatic stimuli--luminance increments, decrements, and phase reversing stimuli--were equally well seen by patients and controls. We conclude that the dopaminergic deficit of retinal amacrine cells in Parkinson patients can be monitored by combined low-contrast and motion (displacement) stimuli. Future studies will determine if moving colored targets are more effective in discriminating patients from controls than are the achromatic gratings used in this work.

An overview of the uses and abuses of electrodiagnosis in ophthalmology

When to use electrodiagnostic procedures and clinical psychophysical procedures, and when not to. The importance of analysing unexplained loss of vision is emphasised.