Rainer Rix

Luminance-contrast evoked responses and color-contrast evoked responses in the human electroretinogram

Pattern electroretinograms to onset-offset stimuli were studied in response to luminance-contrast (e.g. red-black or green-black) and color-contrast (e.g. red-green) stripe patterns of equal luminance. Onset responses to color-contrast patterns show no spatial selectivity and a constant peak latency at all spatial frequencies, a behavior different from that of luminance-contrast evoked responses (spatial selectivity and increasing peak latency with spatial frequency). These results are tentatively related to the physiology of tonic and phasic primate retinal ganglion cells and to the spatially selective and non-selective human contrast sensitivity to respectively luminance-contrast and color-contrast gratings.

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 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.

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.

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.

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.

The pattern ERG in response to colored stimuli

The pattern-evoked electroretinogram (PERG) was studied in response to squarewave 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.

Veränderungen in der äußeren plexiformen Schicht der Kaninchenretina nach langer Gabe von Vincristin

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 dendrites 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. Kaninchen, welche über 6 Wochen Vincristin intravenös erhalten hatten, zeigten nach einem Jahr unter anderem Veränderungen in der äußeren plexiformen Schicht der Retina, die auf einen Untergang von Rezeptorzellen, bipolaren Ganglienzellen und Horizontalzellen schließen lassen. Häufig waren kompensierte Zellschäden zu beobachten, die im Cytoplasma mit Verlust von Miktrotubuli, Autolysevakuolen, Ablagerung granulären Materials und Membranveränderungen am Ribbonkomplex einhergingen. Bei einem Vergleich von Axonen und Dendriten fällt ein Überwiegen der geschädigten Dendriten auf. Da nach kurzen Gaben von Vincristin bislang vergleichbare Beobachtungen nicht mitgeteilt wurden, stellt sich ein unterschiedliches Regenerationsvermögen zur Erörterung, das im endoplasmatischen Retikulum begründet sein könnte.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 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).

Die Gleichspannungsantwort im Elektroretinogramm des Menschen während unterschiedlicher Wachheitsgrade

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 subjects 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 subjects 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. The ERG remains uninfluenced by the degree of the subjects vigilance. 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. Es wird über die Gleichspannungskomponente im ERG des Menschen bei Reizung mit Rotlicht verschiedener Intensitäten und unter Bedingungen eines wechselnden Wachheitsgrades berichtet. Ein Maß für letzteren vermitteln bestimmte Frequenzanteile im Leistungsspektrum des Occipital-EEG. 1. Das ERG bleibt von der Vigilanzlage der Versuchsperson unbeeinflußt. 2. Rotes Reizlicht erweist sich in besonderer Weise dazu geeignet, photopische und skotopische Antworten im on-Effekt, möglicherweise auch im offEffekt, getrennt auszulösen. Der Gleichspannungsanteil ist als Teilkomponente der skotopischen b-Welle anzusehen. Die photopische x-Welle läßt sich bis zu niedrigen Reizstärken zurückverfolgen und bleibt vom Gleichspannungspotential deutlich getrennt. Das ERG bleibt von der Vigilanzlage der Versuchsperson unbeeinflußt. Rotes Reizlicht erweist sich in besonderer Weise dazu geeignet, photopische und skotopische Antworten im on-Effekt, möglicherweise auch im offEffekt, getrennt auszulösen. Der Gleichspannungsanteil ist als Teilkomponente der skotopischen b-Welle anzusehen. Die photopische x-Welle läßt sich bis zu niedrigen Reizstärken zurückverfolgen und bleibt vom Gleichspannungspotential deutlich getrennt.