The sequential processing of visual motion in the human electroretinogram and visual evoked potential

Mechanisms of motion vision in the human have been studied extensively by psychophysical methods but less frequently by electrophysiological techniques. It is the purpose of the present investigation to study electrical potentials of the eye (electroretinogram, ERG) and of the brain (visual evoked potential, VEP) in response to moving regular square-wave stripe patterns spanning a wide range of contrasts, spatial frequencies, and speeds. The results show that ERG amplitudes increase linearly with contrast while VEPs, in agreement with the literature, show an amplitude saturation at low contrast. Furthermore, retinal responses oscillate with the fundamental temporal stimulus frequency of the moving pattern while brain responses do not. In both the retina and the brain, the response amplitudes are tuned to certain speeds which is in agreement with the nonlinear correlation-type motion detector. Along the ascending slopes (which means increasing amplitudes) of the tuning functions, the ERG curves overlap at all spatial frequencies if plotted as a function of temporal stimulation frequency. The ascending slopes of the tuning functions of the VEP overlap if plotted as a function of speed. The descending slopes (which means decreasing amplitudes) of the tuning functions show little (ERG) or no (VEP) overlap and the waveforms at high speeds approach pattern-offset-onset responses. These observations suggest that in the retina motion processing along the ascending slopes of the tuning curves takes place by coding the temporal stimulation frequency which depends on the spatial frequency of the moving pattern. In the brain, however, motion processing is by speed independent of spatial frequency. Simple calculations show that the VEP information is decoded from the ERG signal into a speed signal.

Interactions of spectral, spatial, and temporal mechanisms in the human pattern visual evoked potential

The human pattern onset-offset visual evoked potential (VEP) was studied with different colours and spatial frequencies presented on a steady homogeneous intensive yellow background. Under this condition a broad, late negative wave (N2) dominated by the blue-sensitive mechanism and a sharper earlier positive wave (P1) dominated by the red-green-sensitive mechanism can be observed. With a 460 nm pattern N2 shows a strong amplitude tuning at low-medium spatial frequencies. With 550 nm an early negative component (N1) is added showing an amplitude tuning at high spatial frequencies. Different spatial resolutions of the two colour mechanisms are thus indicated. With pattern-reversal stimuli the 550 nm stimulus shows a higher temporal resolution than the 460 nm stimulus.

[Blue-sensitive mechanisms in pattern ERG and VEP]

Pattern onset-offset ERGs and VEPs in response to square-wave stripe patterns of different wavelengths and spatial frequencies under chromatic yellow adaptation (two-channel Maxwellian view) were studied in three subjects. One channel provided a steady homogeneous adapting field of 570 nm, while the other channel, containing the patterns, was superimposed on the adapting field (33 degrees). The spectral sensitivity curve of the ERG had a prominent peak in the blue (460 nm) and a shoulder in the red and green (above 500 nm). For wavelengths below 500 nm the shape of the psychophysically determined sensitivity curve to the onset and offset of the pattern was in close agreement with the electroretinal sensitivity curves determined for a low-amplitude criterion. With almost all wavelengths there were two components in the same VEP response at the same time: a slow negative wave with maximum sensitivity at 460 nm and an earlier fast positive component with maximum sensitivity in the red-green region. When the spatial frequency of a 460 nm test pattern was varied under yellow adaptation the onset response in the ERG showed only very slight spatial tuning. In the onset response of the VEP, however, the slow component showed prominent spatial tuning (around 2 c/deg) under the same conditions.

Spatial and chromatic interactions in the human pattern electroretinogram

The spectral sensitivity and the spatial selectivity was studied both psychophysically and electroretinographically using the pattern onset-offset paradigm. All measurements were made under intensive yellow adaptation. The spectral sensitivity functions of both measures were in close agreement. They showed a peak at 460 nm (blue-sensitive mechanism) and a shoulder around 550 nm (red-green-sensitive mechanism). The luminance curves of the pattern onset ERG obtained with long wavelengths had a steeper slope and reached larger amplitudes than those obtained with short wavelengths. In addition the response-peak times were longer with short wavelengths. When the spatial frequency of the pattern was varied the 460 nm-onset responses showed very little or no spatial tuning and long peak times (around 60 msec). This was ascribed to the contribution from only one type of ganglion cell, namely the blue-yellow opponent receptive fields lacking a center-surround organization. The 550 nm-onset responses showed a clear spatial tuning (4 c/deg) and an increase in peak time (40-50 msec) with increasing spatial frequency (0.26-9.2 c/deg). This was ascribed to different types of receptive fields having a center-surround structure.

The different contributions of local luminance decreases and increases to the pattern electroretinogram (PERG)

The typical pattern-onset-offset stimulus (stimulus A) consisting of local luminance increases and decreases was broken down into stimuli presenting only local luminance increases (stimulus B) or only local luminance decreases (stimulus C). With stimulus B the onset ERGs are luminance responses. With stimulus C the onset ERGs are pattern-related responses showing a spatial band-pass function. With stimulus A the response is a linear addition of responses to stimuli B and C. The simultaneously recorded VEP is a pattern-related response with all three stimuli (A-C).

Differences between pattern onset and pattern reversal retinal responses

The pattern-evoked electroretinogram was recorded to pattern onset-offset and pattern reversal stimuli in two color-normal subjects with either luminance contrast of black-red (600 nm) and black-green (526 nm) square-wave stripe patterns or color contrast red-green patterns. The size of the onset response shows a spatial tuning with luminance contrast patterns and only a simple low-pass filter function with color contrast patterns. The peak latency of the response to luminance contrast increases with increasing spatial frequency but stays constant with color contrast patterns. The size of the reversal responses, however, shows only a low-pass filter function under both contrast conditions. The peak latency to luminance contrast shows a slight increase and to color contrast it remains constant with increasing spatial frequency. The differences noted under the various stimulus conditions must take into account the possible effects of different luminance modulation depths of onset and reversal stimuli, the modulation transfer function of the eye, and the activity of luminance-antagonistic and color-antagonistic receptive fields.

Electrical responses of the human eye to changes in saturation of the stimulating light

Previous studies on color vision using the electroretinogram or the evoked potential have concentrated only on brightness and hue but not on the saturation of color. In the present investigation patterns of alternate stripes of a highly saturated color and a totally desaturated color (= white) of equal brightness were presented in the pattern-reversal mode. It can be demonstrated that the reading obtained is in agreement with psychophysical saturation scale data of earlier investigators.

The pattern ERG in response to colored stimuli

The pattern-evoked electroretinogram (PERG) was studied in response to square-wave stripe patterns contrasting either between dark and colored stripes ("red-black" or "green-black" luminance contrast pattern) or between the two colors (red-green chromatic contrast pattern). All lights were matched in photopic luminance. A two-channel Maxwellian view system was used to present the stimuli in the onset-offset mode. When no pattern was present a mixture of both colors was seen. Different spatial frequencies were studied and the amplitudes of the onset response were evaluated. When the two luminance contrast patterns were presented, the responses showed a spatial selectivity. However the combination of the two colors (red-green contrast) resulted in a monotonic decrease of the response with spatial frequency. The spatially selective behavior of the response to luminance contrast patterns could be associated with the on-off center-surround organization of retinal receptive fields. The behavior of the response to chromatic-contrast patterns, on the other hand, could be explained by the action of color-opponent center-surround receptive fields as described in the primate.

Changes in spatial selectivity of pattern-ERG components with stimulus contrast

Electrical mass responses of the visual system to stripe patterns of varying fineness (spatial frequency) can show either an amplitude maximum at a medium spatial frequency, a behavior termed "spatial selectivity," or a monotonic decrease in amplitude with increasing spatial frequency. The former behavior is probably mediated by neurons having a center-surround receptive field structure and the latter by neurons lacking this antagonism. The pattern-evoked human electroretinogram was studied in this report using different spatial frequencies and pattern contrasts. The positive component of the response showed a spatial selectivity only at low contrast but was not spatially selective at the highest contrast. The negative component showed a spatial selectivity at all contrast levels. The data indicate that if pattern-related responses activated by antagonistic receptive fields are to be studied, low contrast values should be employed and attention should be paid to the negative component of the response.

Spatial contrast transfer functions of the pattern-evoked electroretinogram

Pattern ERGs in response to pattern-reversal stimuli varying in spatial frequency (range: 0.2-9.03 cycles/deg) and contrast (range: 0.03-0.93) were recorded from two normal male subjects. At most spatial frequencies the response amplitude increased linearly up to the highest contrast without saturation. From the amplitude-versus-contrast plots spatial contrast-transfer functions were derived for different levels of contrast. The sensitivity of the reversal response showed a spatial selectivity around 4 cycles/deg, which was more pronounced at low, rather than at high, contrast values. Good agreement with the psychophysical contrast-sensitivity curve was found. The procedure described permits a quantitative analysis of the sensitivity of the retina to spatial contrast stimuli and could be helpful in the diagnosis of diseases of the eye and the optic nerve.

[Carrier state in X-linked ocular albinism: a proof of the validity of Lyon's hypothesis in man]

The finding of an irregular patchy fundus pigmentation in the mother of a boy with ocular albinism was interpreted as Lyon's effect on the fundus, i.e., the mosaic-like effect caused by a pathologic X-chromosome in the female carrier. It was thus possible to diagnose the more frequent X-linked form in this family.

Effect of stimulus intensity and contrast on the pattern ERG

Stripe patterns of varying spatial frequency were presented in the onset-offset mode. At a high contrast the amplitude of the onset response showed a spatial selectivity which occurred with a high intensity at a higher spatial frequency than with a low intensity. The offset response showed only a monotonic decrease in amplitude at both intensities. Contrast sensitivity functions were derived at different levels of contrast. The spatial selectivity of the onset response occurred at a contrast spatial frequency and was more pronounced with low contrasts. The amplitude of the offset response was spatially selective only at low contrasts; with increasing contrast a gradual shift to a non-selective behavior was noted.

Information coding in the visual system: a new hypothesis

Experiments on subjective color sensations using a special signal generator and a standard TV monitor (black and white) led to a new hypothesis on information coding in the visual system. According to this hypothesis a trigger signal is required which restores the phase correlation of the pulse-coded spiking of the neurons transmitting visual information from the eye to the brain. The "shift effect" ("periphery effect"), either artificially induced or initiated by microsaccades, might act as the postulated trigger.

[Changes in the outer plexiform layer of the rabbit retina after long-term application of vincristine]

Rabbits which had been intravenously injected with Vincristine for six weeks showed changes in the outer plexiform layer of the retina after one year, which suggests the destruction of receptor cells, bipolar ganglion cells, and horizontal cells. Compensated cell damage accompanied by loss of microtubuli in the cytoplasma, autolytic vacuoles, granular material deposits, and membrane changes of the ribbon complex were frequently observed. A comparison between axons and dendrites showed a predominance of damaged dendritis over axons. Because short-term studies have not produced the same results, different regeneration capacities, which might have their origin in the endoplasmatic reticulum, are discussed.

[The influence of vigilance on DC response in human visual evoked potential (author's transl)]

Visual evoked cortical potentials elicited by long-lasting stimuli of red light were examined in eight subjects under different conditions of vigilance. The DC components of the evoked potentials were compared with the delta and theta activity (0-7.5 Hz) of the EEG by means of frequency power spectra. The results are: 1) A proportional relationship exists between the amplitude of the negative DC component of the evoked potential and the theta and delta activity in the EEG. 2) Under conditions of low vigilance the negative DC potential does not return immediately to the baseline after the off-effect. Instead it may reach a second peak. 3) Under conditions of high vigilance, the DC potential may reverse its polarity. Its return to the baseline following the off-effect is immediate. 4) No dependence of the cortical DC potential on the intensity of the light stimulus could be demonstrated. 5) Since the negative potential outlasts the visual stimulus and could be recorded at the occiput and the vertex, it may be regarded as a nonspecific arousal reaction. Furthermore, since the positive DC potential can only be recorded at the occiput, it is regarded as a specific stimulus-correlated response.

[Retinographic alterations in different forms of congenital cataracta (author's transl)]

In a follow-up study of patients suffering from congenital cataract, particular attention was paid to the electroretinogram. Besides hereditary lens opacifications and rubella embryopathy, galactosaemia and spontaneous idiopathic hypoglycemia occurring in children and infants were examined. The question, how much biochemical factors can influence the ERG, is becoming more important.

[Hydroxychinoline- and zinc-treated acrodermatitis enteropathica and electroretinographic findings (author's transl)]

A meanwhile 13 years old boy had to be treated by hydroxychinolines for a severe acrodermatitis enteropathica since his 1st year of life. At the age of 5 years he showed visual deterioration by atrophia optici. Dose reduction and application of different halogen substitutions were tried. Finally, it was daily oral zinc application and continuous control of the serum zinc level which made disappear all cutaneous and mucous symptoms. At an unchanged ophthalmoscopic status, there occurred a slight raise of vision, an enlargement of peripheric campus and a normalization of the electroretinographic potentials.

[The D.C. response in the human electroretinogram under different degrees of wakefulness (author's transl)]

A report is given on the D.C. component of the human ERG following stimulation with red light of varying intensities and under different conditions of vigilance. The degree of the subject's wakefulness can be followed by looking at certain frequency components of the power spectrum of the occipital EEG. 1. The ERG remains uninfluenced by the degree of the subject's vigilance. 2. Red light is especially suited for eliciting separately photopic an scotopic responses in the on-effect of the ERG, possibly in the off-effect also. The D.C. potential is regarded as a component of the scotopic b-wave. The photopic x-wave can be recorded with very low stimulus intensities and stays clearly separated from the D.C. component.

[A histological and electron microscopic study of the rabbit retina after application of vincristin (author's transl)]

Temporary electrophysiological damage to the rabbit eye proportional to dosis and application time was observed after application of Vincristin (Lilly). Cell destruction in all retinal layers was observed upon histological and electron microscopic examination of the animals. The outer segments of the receptor cells showed chiefly diffuse damage, and the pigment epithelial cells showed a high incidence of reorganization. Follow-up examination one year later showed this damage to be partially reparable, especially when very high doses had not been applied. Regeneration of the outer segments was observed. Destruction through pyknosis of the nucleus and cytoplasmal destruction was observed in a small number of receptor cells, bipolar ganglion cells, and ganglion cells. This also explained the absence of lasting functional abnormalities in the ERG and EVP.

[Alport-syndrom with participation of the cornea and alterations of ERG (author's transl)]

A description of a 26-year-old patient who had hearing difficulties, progressive nephropathy, and conus of the lens in both eyes is given. The ERG was below normal and the EOG remained normal. About the same time the nephropathy affliction occurred, a ringed abscess appeared in the left eye. Afterwards it healed with a scar, but half a year later the same affliction appeared in the right eye.