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Sönke Johnsen - One of the best experts on this subject based on the ideXlab platform.
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a chiton uses aragonite lenses to form images
Current Biology, 2011Co-Authors: Daniel I Speiser, Douglas J. Eernisse, Sönke JohnsenAbstract:Summary Hundreds of ocelli are embedded in the dorsal shell plates of certain chitons [1]. These ocelli each contain a pigment layer, retina, and lens [2], but it is unknown whether they provide chitons with Spatial Vision [3]. It is also unclear whether chiton lenses are made from proteins, like nearly all biological lenses, or from some other material [4]. Electron probe X-ray microanalysis and X-ray diffraction revealed that the chiton Acanthopleura granulata has the first aragonite lenses ever discovered. We found that these lenses allow A. granulata 's ocelli to function as small camera eyes with an angular resolution of about 9°–12°. Animals responded to the sudden appearance of black, overhead circles with an angular size of 9°, but not to equivalent, uniform decreases in the downwelling irradiance. Our behavioral estimates of angular resolution were consistent with estimates derived from focal length and receptor spacing within the A. granulata eye. Behavioral trials further indicated that A. granulata 's eyes provide the same angular resolution in both air and water. We propose that one of the two refractive indices of the birefringent chiton lens places a focused image on the retina in air, whereas the other does so in water.
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a chiton uses aragonite lenses to form images
Current Biology, 2011Co-Authors: Daniel I Speiser, Douglas J. Eernisse, Sönke JohnsenAbstract:Summary Hundreds of ocelli are embedded in the dorsal shell plates of certain chitons [1]. These ocelli each contain a pigment layer, retina, and lens [2], but it is unknown whether they provide chitons with Spatial Vision [3]. It is also unclear whether chiton lenses are made from proteins, like nearly all biological lenses, or from some other material [4]. Electron probe X-ray microanalysis and X-ray diffraction revealed that the chiton Acanthopleura granulata has the first aragonite lenses ever discovered. We found that these lenses allow A. granulata 's ocelli to function as small camera eyes with an angular resolution of about 9°–12°. Animals responded to the sudden appearance of black, overhead circles with an angular size of 9°, but not to equivalent, uniform decreases in the downwelling irradiance. Our behavioral estimates of angular resolution were consistent with estimates derived from focal length and receptor spacing within the A. granulata eye. Behavioral trials further indicated that A. granulata 's eyes provide the same angular resolution in both air and water. We propose that one of the two refractive indices of the birefringent chiton lens places a focused image on the retina in air, whereas the other does so in water.
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Spatial Vision in the purple sea urchin strongylocentrotus purpuratus echinoidea
The Journal of Experimental Biology, 2010Co-Authors: D Yerramilli, Sönke JohnsenAbstract:SUMMARY Recent evidence that echinoids of the genus Echinometra have moderate visual acuity that appears to be mediated by their spines screening off-axis light suggests that the urchin Strongylocentrotus purpuratus , with its higher spine density, may have even more acute Spatial Vision. We analyzed the movements of 39 specimens of S. purpuratus after they were placed in the center of a featureless tank containing a round, black target that had an angular diameter of 6.5 deg. or 10 deg. (solid angles of 0.01 sr and 0.024 sr, respectively). An average orientation vector for each urchin was determined by testing the animal four times, with the target placed successively at bearings of 0 deg., 90 deg., 180 deg. and 270 deg. (relative to magnetic east). The urchins showed no significant unimodal or axial orientation relative to any non-target feature of the environment or relative to the changing position of the 6.5 deg. target. However, the urchins were strongly axially oriented relative to the changing position of the 10 deg. target (mean axis from –1 to 179 deg.; 95% confidence interval ± 12 deg.; P P −10 ; Monte Carlo simulation), showing that each urchin, whether it moved towards or away from the target, did so with high consistency. These results strongly suggest that S. purpuratus detected the 10 deg. target, responding either by approaching it or fleeing it. Given that the urchins did not appear to respond to the 6.5 deg. target, it is likely that the 10 deg. target was close to the minimum detectable size for this species. Interestingly, measurements of the spine density of the regions of the test that faced horizontally predicted a similar visual resolution (8.3±0.5 deg. for the interambulacrum and 11±0.54 deg. for the ambulacrum). The function of this relatively low, but functional, acuity – on par with that of the chambered Nautilus and the horseshoe crab – is unclear but, given the bimodal response, is likely to be related to both shelter seeking and predator avoidance.
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Spatial Vision in the echinoid genus echinometra
The Journal of Experimental Biology, 2004Co-Authors: Erin Blevins, Sönke JohnsenAbstract:SUMMARY Although eyes are generally considered necessary for image resolution, a diffuse photoreceptive system with directional sensitivity may also have this ability. Two species of the echinoid genus Echinometra were tested for Spatial Vision by examining their ability to locate and move towards targets of different sizes. The echinoids were significantly oriented ( P <0.0001) towards a target with an angular width of 33° (0.3 sr) but were not oriented to targets with angular widths of 26° and 16°. This ability is probably due to the blocking of off-angle light by the spines, which have approximately the correct spacing for the observed resolution. Spatial Vision is advantageous for echinoids of this genus because they leave and return to small dark shelters. This first demonstration of Spatial Vision in an echinoderm sheds further light on the complex optical structures and photobehaviors found in this phylum.
Dennis M Levi - One of the best experts on this subject based on the ideXlab platform.
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reduced sampling efficiency causes degraded vernier hyperacuity with normal aging vernier acuity in position noise
Scientific Reports, 2012Co-Authors: Dennis M Levi, Roger W Li, Brian Brown, Marion H Edwards, Sandy W ChatAbstract:Vernier acuity, a form of visual hyperacuity, is amongst the most precise forms of Spatial Vision. Under optimal conditions Vernier thresholds are much finer than the inter-photoreceptor distance. Achievement of such high precision is based substantially on cortical computations, most likely in the primary visual cortex. Using stimuli with added positional noise, we show that Vernier processing is reduced with advancing age across a wide range of noise levels. Using an ideal observer model, we are able to characterize the mechanisms underlying age-related loss, and show that the reduction in Vernier acuity can be mainly attributed to the reduction in efficiency of sampling, with no significant change in the level of internal position noise, or Spatial distortion, in the visual system.
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detecting disorder in Spatial Vision
Vision Research, 2000Co-Authors: Dennis M Levi, Stanley A Klein, Vineeta Sharma, Lisa NguyenAbstract:In normal foveal Vision, visual space is accurately mapped from retina to cortex. However, the normal periphery, and the central field of strabismic amblyopes have elevated position discrimination thresholds, which have often been ascribed to increased ‘intrinsic’ Spatial disorder. In the present study we evaluated the sensitivity of the human visual system (both normal and amblyopic) to Spatial disorder, and asked whether there is increased ‘intrinsic’ topographical disorder in the amblyopic visual system. Specifically, we measured thresholds for detecting disorder (two-dimensional Gaussian position perturbations) either in a horizontal string of N equally spaced samples (Gabor patches), or in a ring of equally spaced samples over a wide range of feature separations. We also estimated both the ‘equivalent intrinsic Spatial disorder’ and sampling efficiency using an equivalent noise approach. Our results suggest that both thresholds for detecting disorder, and equivalent intrinsic disorder depend strongly on separation, and are modestly increased in strabismic amblyopes. Strabismic amblyopes also show markedly reduced sampling efficiency. However, neither amblyopic nor peripheral Vision performs like ideal or human observers with added separation-independent positional noise. Rather, the strong separation dependence suggests that the ‘equivalent intrinsic disorder’ may not reflect topographic disorder at all, but rather may reflect an abnormality in the amblyopes’ Weber relationship. © 2000 Elsevier Science Ltd. All rights reserved.
Hans Strasburger - One of the best experts on this subject based on the ideXlab platform.
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a generalized cortical magnification rule predicts low contrast letter recognition in the visual field
Journal of Vision, 2010Co-Authors: Hans StrasburgerAbstract:Harvey L O Jr (1997). Efficient estimation of sensory thresholds with ML-PEST. Spatial Vision 11(1), 121-128. Strasburger H (1997). R_Contrast: Rapid measurement of recognition contrast thresholds. Spatial Vision 10, 495-498. Strasburger H (2001). Converting between measures of slope of the psychometric function. Perception & Psychophysics 63, 1348-1355. Strasburger H (2001). Invariance of the psychometric function for letter recognition across the visual field. Perception & Psychophysics 63, 1356-1376. Strasburger H & Rentschler I (1996). Contrast-dependent dissociation of visual recognition and detection fields. European Journal of Neuroscience 8, 1787-1791. Strasburger H, Rentschler I & Harvey L O Jr (1994). Cortical magnification theory fails to predict visual recognition. European Journal of Neuroscience 6, 1583-1588. Strasburger H (2002). Indirektes Sehen. Formerkennung im zentralen und peripheren Gesichtsfeld. Hogrefe: Gottingen, Bern, Toronto, Seattle. A generalized cortical magnification rule predicts low-contrast letter recognition in the visual field Hans Strasburger Generation Research Program, Human Studies Center, University of Munchen strasburger@uni-muenchen.de —— www.hans.strasburger.de .
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assessing Spatial Vision automated measurement of the contrast sensitivity function in the hooded rat
Journal of Neuroscience Methods, 2000Co-Authors: Jason Keller, Hans Strasburger, Daniel T Cerutti, Bernhard A SabelAbstract:Abstract The contrast-sensitivity function (CSF) provides a concise and thorough description of an organism’s Spatial Vision; it is widely used to describe Vision in animals and humans, to track developmental changes in Vision, and to compare Vision among different species. Despite the predominance of rats in neuroscience research, their Vision is not thoroughly studied due to the complexity of psychophysical measurement and a generally held notion that rat Vision is poor. We therefore designed an economical and rapid method to assess the hooded rat’s CSF, using a computer monitor to display stimuli and an infrared touch screen to record responses. A six-alternative forced-choice task presented trials in which a sine-wave grating (S+), varying in Spatial frequency and contrast, was displayed at different locations along with five gray stimuli (S−). Nose pokes to the S+ but not the S− produced water reinforcers. Contrasts were tested at each Spatial frequency with a simple adaptive procedure until stimulus detection fell below chance. Psychometric functions were obtained by maximum-likelihood fitting of a logistic function to the raw data, obtaining the threshold as the function’s point of inflection. As in previous studies with rats, CSFs showed an inverse-U shape with peak sensitivity at 0.12 cyc/deg and acuity just under 1 cyc/deg. The results indicate the present computer-controlled behavioral testing device is a precise and efficient instrument to assess Spatial visual function in rats.
Laure Pisella - One of the best experts on this subject based on the ideXlab platform.
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An ‘automatic pilot’ for the hand in human posterior parietal cortex: toward reinterpreting optic ataxia
Nature Neuroscience, 2000Co-Authors: Laure Pisella, G Gréa, C. Tilikete, A. Vighetto, D Desmurget, G. Rode, D. Boisson, Y. Rossetti, H. GréaAbstract:We designed a protocol distinguishing between automatic and intentional motor reactions to changes in target location triggered at movement onset. In response to target jumps, but not to a similar change cued by a color switch, normal subjects often could not avoid automatically correcting fast aiming movements. This suggests that an 'automatic pilot' relying on Spatial Vision drives fast corrective arm movements that can escape intentional control. In a patient with a bilateral posterior parietal cortex (PPC) lesion, motor corrections could only be slow and deliberate. We propose that 'on-line' control is the most specific function of the PPC and that optic ataxia could result from a disruption of automatic hand guidance.
Lauren Sumnerrooney - One of the best experts on this subject based on the ideXlab platform.
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extraocular Vision in a brittle star is mediated by chromatophore movement in response to ambient light
Current Biology, 2020Co-Authors: Lauren Sumnerrooney, John D Kirwan, Elijah K Lowe, Esther UllrichluterAbstract:Summary Almost all animals can sense light, but only those with Spatial Vision can “see.” Conventionally, this was restricted to animals possessing discrete visual organs (eyes), but extraocular Vision could facilitate Vision without eyes. Echinoderms form the focus of extraocular Vision research [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ], and the brittle star Ophiocoma wendtii, which exhibits light-responsive color change and shelter seeking, became a key species of interest [ 4 , 8 , 9 ]. Both O. wendtii and an apparently light-indifferent congeneric, O. pumila, possess an extensive network of r-opsin-reactive cells, but its function remains unclear [ 4 ]. We show that, although both species are strongly light averse, O. wendtii orients to stimuli necessitating Spatial Vision for detection, but O. pumila does not. However, O. wendtii’s response disappears when chromatophores are contracted within the skeleton. Combining immunohistochemistry, histology, and synchrotron microtomography, we reconstructed models of photoreceptors in situ and extracted estimated angular apertures for O. wendtii and O. pumila. Angular sensitivity estimates, derived from these models, support the hypothesis that chromatophores constitute a screening mechanism in O. wendtii, providing sufficient resolving power to detect the stimuli. RNA sequencing (RNA-seq) identified opsin candidates in both species, including multiple r-opsins and transduction pathway constituents, congruent with immunohistochemistry and studies of other echinoderms [ 10 , 11 ]. Finally, we note that differing body postures between the two species during experiments may reflect aspect of signal integration. This represents one of the most detailed mechanisms for extraocular Vision yet proposed and draws interesting parallels with the only other confirmed extraocular visual system, that of some sea urchins, which also possess chromatophores [ 1 ].
