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PubMed1989

Spatial summation and visual adaptation in the inner part of the frog retina.

The spatial summation of the proximal negative response (PNR) of frog retina was analyzed during different states of adaptation induced by repetitive light stimulation with either 15 sec or 1 min interstimulus interval. The spatial summation area of the PNR was found to be wider during relatively more dark adapted conditions compared to relatively more light adapted ones. This finding indicates that lateral mechanisms in the inner network of the retina seem to be activated by adapting stimuli. Secondly, the results suggest that the activity of the amacrines, as reflected by the PNR, may initiate the series of neuronal events which underlie the oscillatory potentials (OPs) of the electroretinogram (ERG).

Adaptation, Ocular↗

PubMed1994

Filter goggles imitating dark adaptation for measurement of visual readaptation after flash exposure.

The effect of red pass goggles (cut off wavelength = 650 nm) imitating dark adaptation on measurement of visual readaptation after flash exposure was investigated in humans. The results showed that there is no statistically significant difference between visual readaptation time measured with ordinary dark adaptation and that with goggles for adaptation. No statistically significant difference was found between females and males. It is suggested that red pass goggles can be practicably used to simulate dark adaptation in measuring visual readaptation time. Visual readaptation time was measured as the interval between the triggering of a green flash and the reappearance of optokinetic nystagmus. Optokinetic nystagmus was induced by a moving vertical grating and recorded by DC EOG.

Adaptation, Ocular↗

PubMed1970

Rod-cone independence for sensitizing interaction in the human retina.

1. Illumination of a retinal area adjoining a tested area can cause either desensitization or sensitization through lateral interaction, depending on whether the distance separating the illuminated and tested areas is small or large. This interaction occurs both in the rod and the cone mechanisms of the retina when each is tested separately by selection of appropriate adapting and testing stimuli.2. In the mixed rod/cone region of the near periphery of the human retina the spatial parameters of interaction within the rod and cone systems were different when mapped out by using only one kind of adapting stimulus and sampling the excitatory state of the rod and cone systems by different probing stimuli.3. Sensitizing interaction signals generated by the rod system are incapable of causing sensitization of the cone system.

Adaptation, Ocular↗

PubMed1971

The independence of the temporal integration properties of individual chromatic mechanisms in the human eye.

1. Since it has been shown by Stiles that the adaptive states of the primary chromatic (pi) mechanisms of the human eye vary independently and since recent theories of visual function have postulated an intimate relation between sensitivity and the temporal characteristics of the retinal response, it is asked whether the temporal integration properties of the eye depend upon the state of adaptation of the retina as a whole or vary independently for each of the chromatic mechanisms.2. It is found that the critical duration, or limit of time-intensity reciprocity, for the detection of monochromatic increments presented on monochromatic background fields depends only upon the adaptive state of the individual pi mechanism mediating the detection. Our results support the hypothesis that each chromatic mechanism has its own automatic gain control.3. At both dark-adapted and asymptotic levels the critical durations for the short wave-length mechanisms appear to be greater than those for pi(4) and pi(5).4. When 500 nm test flashes are presented on 600 nm adaptation fields, critical durations increase at high background intensities. This anomaly adds further support to the hypothesis that the critical durations of different chromatic mechanisms vary independently, since 500 nm flashes are probably detected by pi(1), rather than by pi(4), when presented on long wave-length adaptation fields of high energy.5. Our findings provide partial support for the suggestion that the Fechner-Benham subjective colours are due to differences in the time constants of the different colour mechanisms.6. It is concluded that the critical duration is principally determined at a very distal stage in the visual system before interactions occur between chromatic mechanisms.

Adaptation, Ocular↗

PubMed1981

Receptive fields of frog retinal ganglion cells: response formation and light-dark-adaptation.

1. The excitatory and inhibitory receptive field mechanisms of retinal ganglion cells were studied by extracellular recording from the eyecup of Rana temporaria in order to elucidate the nature of adaptational changes in the functioning of the receptive field. 2. The responses to large stimuli were always strongly depressed relative to responses evoked by smaller spots. This was true even in the fully dark-adapted state and at the very lowest stimuli intensities. 3. Threshold measurements confirmed earlier findings, usually revealing the surround only in light-adapted states. However, in more than 10% of fully dark-adapted cells thresholds to large stimuli were significantly elevated. 4. The central summation area of the receptive field was found to shrink with light-adaptation. There was a gradual decrease in diameters, amounting to some 20-30%, from the dark-adapted, rod-determined receptive fields to the cone-determined ones. 5. Adaptation by bleaching and adaptation by backgrounds changed the effects of the surround in different ways. After a rhodopsin bleach the transition from a light-adapted to a dark-adapted situation was seen as an abrupt drop of large-stimulus thresholds at some time during adaptation. Steady backgrounds produced no such dramatic changes, but the increment threshold lines were somewhat steeper with test spots stimulated the surround than with smaller spots. 6. Although the discharge patterns generally show the strength of the surround influence, they underwent no qualitative change at the time of the drop of large-stimulus thresholds after a bleach. 7. It is suggested that the drop does not reflect a sudden reorganization of the receptive field, but is the consequence of the different ways the response to large stimuli are formed in different ranges of stimulus intensity (pre-inhibitory at high intensities, post-inhibitory at low intensities), and of gradual changes in signal dynamics.

Action Potentials↗

PubMed1990

Background and bleaching adaptation in luminosity type horizontal cells in the isolated turtle retina.

1. The effects of background illumination and bleached photopigment on luminosity type horizontal cells were studied in the isolated turtle retina. 2. Background illumination, which produced less than 60% bleaching, hyperpolarized and desensitized the horizontal cells to a degree which depended upon the background intensity. The desensitization of horizontal cells by these backgrounds is described by a Weber-Fechner type relationship. This desensitization primarily reflects the activation of a 'gain reduction' mechanism and cannot be accounted for by 'response compression'. 3. Following the termination of these backgrounds, horizontal cell sensitivity partially recovered but did not return to the pre-background, dark-adapted level. This desensitization was attributed to the presence of bleached photoproducts which were produced by the background exposure. 4. Application of very bright backgrounds caused the horizontal cells to initially hyperpolarize, and then to gradually depolarize towards the dark-adapted level along an exponential time course which appeared to reflect the decreased quantal catching associated with very high levels of photopigment bleaching. 5. From the time constant of the exponential decay of horizontal cell potential during the bright background illumination, the photosensitivity to bleaching of the cone photopigment was determined to be 4.5 x 10(7) effective quanta (633 nm) microns-2. 6. After termination of bright backgrounds which bleached more than 99% of the cone photopigment, the horizontal cell sensitivity increased linearly with time and after 25 min reached a level which was about 15% of the pre-background sensitivity. 7. Bleached photopigment reduces light sensitivity via at least two different mechanisms. For moderate degrees of bleaching (less than 95%), the presence of bleached photoproducts plays the major role in sensitivity control, producing a desensitization which is logarithmically related to the fraction of bleached pigment. During extensive bleaching (greater than 99%), the contribution of reduced quantal catching to sensitivity control becomes apparent and produces an additional loss in sensitivity which is linearly related to the fraction of unbleached pigment present.

Adaptation, Ocular↗

PubMed2002

The scotopic threshold response of the dark-adapted electroretinogram of the mouse.

The most sensitive response in the dark-adapted electroretinogram (ERG), the scotopic threshold response (STR) which originates from the proximal retina, has been identified in several mammals including humans, but previously not in the mouse. The current study established the presence and assessed the nature of the mouse STR. ERGs were recorded from adult wild-type C57/BL6 mice anaesthetized with ketamine (70 mg kg(-1)) and xylazine (7 mg kg(-1)). Recordings were between DTL fibres placed under contact lenses on the two eyes. Monocular test stimuli were brief flashes (lambda(max) 462 nm; -6.1 to +1.8 log scotopic Troland seconds(sc td s)) under fully dark-adapted conditions and in the presence of steady adapting backgrounds (-3.2 to -1.7 log sc td). For the weakest test stimuli, ERGs consisted of a slow negative potential maximal approximately 200 ms after the flash, with a small positive potential preceding it. The negative wave resembled the STR of other species. As intensity was increased, the negative potential saturated but the positive potential (maximal approximately 110 ms) continued to grow as the b-wave. For stimuli that saturated the b-wave, the a-wave emerged. For stimulus strengths up to those at which the a-wave emerged, ERG amplitudes measured at fixed times after the flash (110 and 200 ms) were fitted with a model assuming an initially linear rise of response amplitude with intensity, followed by saturation of five components of declining sensitivity: a negative STR (nSTR), a positive STR (pSTR), a positive scotopic response (pSR), PII (the bipolar cell component) and PIII (the photoreceptor component). The nSTR and pSTR were approximately 3 times more sensitive than the pSR, which was approximately 7 times more sensitive than PII. The sensitive positive components dominated the b-wave up to > 5 % of its saturated amplitude. Pharmacological agents that suppress proximal retinal activity (e.g. GABA) minimized the pSTR, nSTR and pSR, essentially isolating PII which rose linearly with intensity before showing hyperbolic saturation. The nSTR, pSTR and pSR were desensitized by weaker backgrounds than those desensitizing PII. In conclusion, ERG components of proximal retinal origin that are more sensitive to test flashes and adapting backgrounds than PII provide the 'threshold' negative and positive (b-wave) responses of the mouse dark-adapted ERG. These results support the use of the mouse ERG in studies of proximal retinal function.

Adaptation, Ocular↗

PubMed1962

Retinal receptor potentials and their linear relationship to light intensity.

After treatment of the isolated retina of a fish (Centropomus) with ammonia (NH(3)), the electrical responses to light are confined to the receptor layer. These receptor responses are fast in light adaptation and very slow in dark adaptation. The light-adapted responses have thresholds 3 to 4 logarithmic units of light intensity higher than the dark- adapted ones. Both kinds of responses are linearly related to light intensity up to the appearance of saturation. Interactions between receptors and adjacent glia cells appear to be involved in adaptation.

Adaptation, Ocular↗

PubMed1971

Light adaptation in the rat retina: evidence for two receptor mechanisms.

Light adapting the rat retina with transient white flashes too dim to bleach a substantial amount of visual pigment produces a change in electroretinogram spectral sensitivity and an increase in flicker fusion frequency. Increment threshold curves obtained with a long wavelength adapting stimulus and a short wavelength test stimulus show rod saturation.

Adaptation, Ocular↗

PubMed1984

Rod-cone interaction in flicker perimetry.

We have assessed the influence of the rod system on cone flicker sensitivity during flicker perimetry. For temporal frequencies above 18 Hz extrafoveal cone-mediated flicker thresholds for a white test stimulus are as much as 1.5 log units lower when measured against a large background light that saturates the rods than when measured in darkness. Following a Ganzfeld bleach extrafoveal cone flicker thresholds are at their minimum once the cones have recovered their sensitivity, but then thresholds rise as the rods begin to recover from the bleach. Our results indicate that the flicker sensitivity of the extrafoveal cone system at high temporal frequencies is influenced by the rods surrounding the flickering test stimulus. The rods reduce flicker sensitivity maximally in the dark adapted state, and their suppressive influence is minimised only by strong rod bleaches or by large backgrounds that saturate the rod system.

Adaptation, Ocular↗

PubMed1998

20-Hz flicker stimulus can isolate the cone function in rat retina.

Cone electroretinograms (ERGs) are typically isolated in humans by flicker stimuli against rod-desensitizing adapting fields. To investigate the manner in which adapting-field luminance affects the cone ERGs, we recorded ERGs in normal albino Sprague-Dawley rats with flicker stimuli presented against adapting fields that ranged in luminance from to 1.75 log cd/m2. A flicker rate of 20 Hz was used to isolate the cone ERGs under all adaptation conditions. We found the amplitudes of cone ERGs to increase with increasing adapting-field luminance. These response characteristics are similar to human ERGs using 30-Hz flicker stimuli, which suggests that flicker stimuli are a useful technique to isolate the cone function in rats.

Adaptation, Ocular↗

PubMed1978