PubMed · 4213077
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H E Kolder. 1974. Electro-oculography.. https://doi.org/10.1159/000307117
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In cephalopods, the complex rhodopsin-retinochrome system serves to regenerate metarhodopsin and metaretinochrome after illumination. In the dark, a soluble protein, retinal-binding protein (RALBP), shuttles 11-cis retinal released from metaretinochrome located in the photoreceptor inner segments to metarhodopsin present in the rhabdoms. While in the rhabdoms, RALBP delivers 11-cis retinal to regenerate rhodopsin and in turn binds the all-trans isomer released by metarhodopsin. RALBP then returns all-trans retinal to the inner segments to restore retinochrome. The conventional interpretation of retinoid cycling is contradicted by immunocytochemical studies showing that, in addition to rhodopsin, retinochrome is present in the rhabdomal compartment, making possible the direct exchange of chromophores between the metapigments with the potential exclusion of RALBP. By using immunofluorescence and laser scanning confocal microscopy, we have precisely located opsin, aporetinochrome, and RALBP in light-/dark-adapted octopus retinas. We found differences in the distribution of all three proteins throughout the retina. Most significantly, comparison of cross sections though light- and dark-adapted rhabdoms showed a dramatic shift in position of the proteins. In the dark, opsin and retinochrome colocalized at the base of the rhabdomal microvilli. In the light, opsin redistributed along the length of the microvillar membranes, and retinochrome retreated to a location that is perhaps extracellular. RALBP was present in the core cytoplasm of the photoreceptor outer segments in the dark, and RALBP moved to the periphery in the light. Because of the colocalization of opsin and retinochrome in the dark, we believe that the two metapigments participate directly in chromophore exchange. RALBP may serve to transport additional chromophore from the inner segments to the rhabdoms and may not be immediately involved in the exchange process.
Visual sensitivity is controlled by at least two distinct types of adaptation: light adaptation adjusts sensitivity to the mean luminance and colour in the stimulus, and contrast adaptation adjusts sensitivity to the variations in luminance and colour. Light adaptation is thought to be important in maintaining the perceived colour of objects despite changes in illumination ('colour constancy'), compensating for the mean changes in the light reflected from scenes under different illuminants. But for naturalistic colour signals, we show here that changes in an illuminant can also alter colour contrasts in images (how colours are distributed around the mean) enough to alter the state of contrast adaptation. Thus perceived colour under different illuminants may also be noticeably influenced by contrast adaptation.
Time series of the durations each eye was dominant during binocular rivalry were obtained psychophysically. The oscillations showed an adaptation effect with mean and standard deviations of rivalry dominance durations increasing as a square root function of time over the course of a trial. The data were corrected for this non-stationarity. Dominance durations had a log-normal probability distribution and the autocorrelation function revealed no short term correlations in the time series. In an attempt to distinguish whether the variability of durations was due to a deterministic, low-dimensional chaotic attractor or to a stochastic process, the data were subjected to two tests. The first was calculation of correlation dimensions and the second was nonlinear forecasting of the time series. Both tests included comparisons with randomized 'surrogate data' as controls. In neither case was there a large difference between test results for actual data and surrogate data. We conclude that chaos is not a major factor underlying variability in binocular rivalry.