查看更多>>摘要：Peripheral worsening in shape discrimination (SD) can be compensated by size-scaling of peripheral stimuli. However, such scaling results in production of large stimuli that occupy a vast range of eccentricities. We used six proportionally decreasing spatial scales to address this pragmatic limitation and to explore how shape discrimination varies with radius in the nasal visual field. Five participants with normal vision discriminated circles and radial frequency (RF) patterns presented nasally to the fixation point at 5 degrees, 10 degrees, 15 degrees and 20 degrees. Stimuli were scaled with the nasal cortical magnification factor (nCMF) from a central stimulus in six spatial scales, which varied from 0.125 to 1, where 1 corresponded to 1.2 degrees radius. Thresholds expressed in Weber fractions remained constant at eccentricities up to 20 degrees regardless of the spatial scale. Weber fractions for the smaller spatial scales (0.125-0.5) were higher and more variable than for the larger spatial scales (0.75-1), yet still constant across periphery. The results provide evidence that peripheral shape discrimination is constrained by low-level properties, such as eccentricity, and can be predicted by the cortical magnification theory. However, above the peripheral modulation resolution limits, RF shape discrimination is based on the proportion between the modulation amplitude and the radius for larger scales (0.75-1), and demonstrates peripheral scale invariance for these stimuli. For eccentric shape discrimination tests, stimuli with low spatial frequency, high contrast, and radii corresponding to SS 0.75-0.875 should be used to ensure constant Weber fractions, small variability, and peripheral stimuli that are not excessively magnified.
查看更多>>摘要：Peripheral worsening in shape discrimination (SD) can be compensated by size-scaling of peripheral stimuli. However, such scaling results in production of large stimuli that occupy a vast range of eccentricities. We used six proportionally decreasing spatial scales to address this pragmatic limitation and to explore how shape discrimination varies with radius in the nasal visual field. Five participants with normal vision discriminated circles and radial frequency (RF) patterns presented nasally to the fixation point at 5 degrees, 10 degrees, 15 degrees and 20 degrees. Stimuli were scaled with the nasal cortical magnification factor (nCMF) from a central stimulus in six spatial scales, which varied from 0.125 to 1, where 1 corresponded to 1.2 degrees radius. Thresholds expressed in Weber fractions remained constant at eccentricities up to 20 degrees regardless of the spatial scale. Weber fractions for the smaller spatial scales (0.125-0.5) were higher and more variable than for the larger spatial scales (0.75-1), yet still constant across periphery. The results provide evidence that peripheral shape discrimination is constrained by low-level properties, such as eccentricity, and can be predicted by the cortical magnification theory. However, above the peripheral modulation resolution limits, RF shape discrimination is based on the proportion between the modulation amplitude and the radius for larger scales (0.75-1), and demonstrates peripheral scale invariance for these stimuli. For eccentric shape discrimination tests, stimuli with low spatial frequency, high contrast, and radii corresponding to SS 0.75-0.875 should be used to ensure constant Weber fractions, small variability, and peripheral stimuli that are not excessively magnified.
Pant, MukundZele, Andrew J.Feigl, BeatrixAdhikari, Prakash...
13页
查看更多>>摘要：Following photopigment bleaching, the rhodopsin and cone-opsins show a characteristic exponential regenera-tion in the dark with a photocycle dependent on the retinal pigment epithelium. Melanopsin pigment regener-ation in animal models requires different pathways to rods and cones. To quantify melanopsin-mediated light adaptation in humans, we first estimated its photopigment regeneration kinetics through the photo-bleach re-covery of the intrinsic melanopsin pupil light response (PLR). An intense broadband light (similar to 120,000 Td) bleached 43% of melanopsin compared to 86% of the cone-opsins. Recovery from a 43% bleach was 3.4X slower for the melanopsin than cone-opsin. Post-bleach melanopsin regeneration followed an exponential growth with a 2.5 min time-constant (tau) that required 11.2 min for complete recovery; the half-bleaching level (Ip) was similar to 4.47 log melanopic Td (16.10 log melanopsin effective photons.cm(-2).s(-1); 8.25 log photoisomerisations.photo-receptor(-1).s(-1)). The effect on the cone-directed PLR of the level of the melanopsin excitation during continuous light adaptation was then determined. We observed that cone-directed pupil constriction amplitudes increased by similar to 10% when adapting lights had a higher melanopic excitation but the same mean photometric luminance. Our findings suggest that melanopsin light adaptation enhances cone signalling along the non-visual retina-brain axis. Parameters tau and Ip will allow estimation of the level of melanopsin bleaching in any light units; the data have implications for quantifying the relative contributions of putative melanopsin pathways to regulate the post-bleach photopigment regeneration and adaptation.
Pant, MukundZele, Andrew J.Feigl, BeatrixAdhikari, Prakash...
13页
查看更多>>摘要：Following photopigment bleaching, the rhodopsin and cone-opsins show a characteristic exponential regenera-tion in the dark with a photocycle dependent on the retinal pigment epithelium. Melanopsin pigment regener-ation in animal models requires different pathways to rods and cones. To quantify melanopsin-mediated light adaptation in humans, we first estimated its photopigment regeneration kinetics through the photo-bleach re-covery of the intrinsic melanopsin pupil light response (PLR). An intense broadband light (similar to 120,000 Td) bleached 43% of melanopsin compared to 86% of the cone-opsins. Recovery from a 43% bleach was 3.4X slower for the melanopsin than cone-opsin. Post-bleach melanopsin regeneration followed an exponential growth with a 2.5 min time-constant (tau) that required 11.2 min for complete recovery; the half-bleaching level (Ip) was similar to 4.47 log melanopic Td (16.10 log melanopsin effective photons.cm(-2).s(-1); 8.25 log photoisomerisations.photo-receptor(-1).s(-1)). The effect on the cone-directed PLR of the level of the melanopsin excitation during continuous light adaptation was then determined. We observed that cone-directed pupil constriction amplitudes increased by similar to 10% when adapting lights had a higher melanopic excitation but the same mean photometric luminance. Our findings suggest that melanopsin light adaptation enhances cone signalling along the non-visual retina-brain axis. Parameters tau and Ip will allow estimation of the level of melanopsin bleaching in any light units; the data have implications for quantifying the relative contributions of putative melanopsin pathways to regulate the post-bleach photopigment regeneration and adaptation.
查看更多>>摘要：The effects of contrast adaptation and contrast area summation (spatial integration) were investigated using a contrast discrimination task. The task consisted of a target of variable size, and a pedestal with a fixed base contrast. Discrimination performance was examined for a condition in which the pedestal size was fixed, equal to the largest target size, and for a condition in which the pedestal size matched the target size and thus varied with it. Repeated performance of the task produced rapid within-session improvements for both conditions. For stimuli with a matching size of target and pedestal, the performance improved only for the larger targets, indicating the development of spatial integration, which was initially absent for these stimuli. However, the improvements were mostly temporary, and were not fully retained between subsequent daily sessions. The temporary nature of the sensitivity gains implies that they resulted, at least in part, from rapid adaptation to the stimulus contrast. We suggest that adaptation decorrelates and thus reduces the spatial noise generated by a high-contrast pedestal, leading to improved spatial integration (area summation) and better contrast sensitivity. A decorrelation model successfully predicted our experimental results.
查看更多>>摘要：The effects of contrast adaptation and contrast area summation (spatial integration) were investigated using a contrast discrimination task. The task consisted of a target of variable size, and a pedestal with a fixed base contrast. Discrimination performance was examined for a condition in which the pedestal size was fixed, equal to the largest target size, and for a condition in which the pedestal size matched the target size and thus varied with it. Repeated performance of the task produced rapid within-session improvements for both conditions. For stimuli with a matching size of target and pedestal, the performance improved only for the larger targets, indicating the development of spatial integration, which was initially absent for these stimuli. However, the improvements were mostly temporary, and were not fully retained between subsequent daily sessions. The temporary nature of the sensitivity gains implies that they resulted, at least in part, from rapid adaptation to the stimulus contrast. We suggest that adaptation decorrelates and thus reduces the spatial noise generated by a high-contrast pedestal, leading to improved spatial integration (area summation) and better contrast sensitivity. A decorrelation model successfully predicted our experimental results.
查看更多>>摘要：People can perceive 3D information from contour drawings and some types of configurations of contours in such drawings are important for 3D perception. We know that our visual system is sensitive to these configurations. Koshmanova & Sawada (2019, Vision Research, 154, 97-104) showed that the sensitivity is higher to a parallel configuration of contours than to a perpendicular configuration of contours. In this study, two psychophysical experiments were conducted that compared the sensitivity to a parallel configuration to two different configurations. In Experiment 1, orientation thresholds were measured with parallel and converging configurations composed of three contours. In Experiment 2, orientation thresholds of configurations composed of two contours were measured with parallel, collinear, and perpendicular configurations. The results of Experiment 1 showed that the visual system is more sensitive to parallel configurations than to converging configurations. The results of Experiment 2 showed that the sensitivity to the parallel configuration is analogous to the sensitivity to the collinear configuration, and it is higher than the sensitivity to the perpendicular configuration. The role that the parallel configuration plays in the 3D perception of contour-drawings is discussed.
查看更多>>摘要：People can perceive 3D information from contour drawings and some types of configurations of contours in such drawings are important for 3D perception. We know that our visual system is sensitive to these configurations. Koshmanova & Sawada (2019, Vision Research, 154, 97-104) showed that the sensitivity is higher to a parallel configuration of contours than to a perpendicular configuration of contours. In this study, two psychophysical experiments were conducted that compared the sensitivity to a parallel configuration to two different configurations. In Experiment 1, orientation thresholds were measured with parallel and converging configurations composed of three contours. In Experiment 2, orientation thresholds of configurations composed of two contours were measured with parallel, collinear, and perpendicular configurations. The results of Experiment 1 showed that the visual system is more sensitive to parallel configurations than to converging configurations. The results of Experiment 2 showed that the sensitivity to the parallel configuration is analogous to the sensitivity to the collinear configuration, and it is higher than the sensitivity to the perpendicular configuration. The role that the parallel configuration plays in the 3D perception of contour-drawings is discussed.
Allen, Rachael S.Motz, Cara T.Singh, AnayeshaHutson, Lauren...
12页
查看更多>>摘要：Blast-induced traumatic brain injury is the signature injury of modern military conflicts. To more fully understand the effects of blast exposure, we placed rats in different holder configurations, exposed them to blast overpressure, and assessed the degree of eye and brain injury. Anesthetized Long-Evans rats received blast exposures directed at the head (63 kPa, 195 dB-SPL) in either an "open holder" (head and neck exposed; n = 7), or an "enclosed holder" (window for blast exposure to eye; n = 15) and were compared to non-blast exposed (control) rats (n = 22). Outcomes included optomotor response (OMR), electroretinography (ERG), and spectral domain optical coherence tomography (SD-OCT) at 2, 4, and 6 months post-blast, and cognitive function (Y-maze) at 3 months. Spatial frequency and contrast sensitivity were reduced in ipsilateral blast-exposed eyes in both holders (p < 0.01), while contralateral eyes showed greater deficits with the enclosed holder (p < 0.05). Thinner retinas (p < 0.001) and reduced ERG a- and b- wave amplitudes (p < 0.05) were observed for both ipsilateral and contralateral eyes with the enclosed, but not the open, holder. Rats in the open holder showed cognitive deficits compared to rats in the enclosed holder (p < 0.05). Overall, the animal holder configuration used in blast exposure studies can significantly affect outcomes. Enclosed holders may cause secondary damage to the contralateral eye by concussive injury or blast wave reflection off the holder wall. Open holders may damage the brain via rapid head movement (contrecoup injury). These results highlight additional factors to be considered when evaluating patients with blast exposure or developing models of blast injury.
Motz, Cara T.Singh, AnayeshaFeola, AndrewHutson, Lauren...
12页
查看更多>>摘要：Blast-induced traumatic brain injury is the signature injury of modern military conflicts. To more fully understand the effects of blast exposure, we placed rats in different holder configurations, exposed them to blast overpressure, and assessed the degree of eye and brain injury. Anesthetized Long-Evans rats received blast exposures directed at the head (63 kPa, 195 dB-SPL) in either an "open holder" (head and neck exposed; n = 7), or an "enclosed holder" (window for blast exposure to eye; n = 15) and were compared to non-blast exposed (control) rats (n = 22). Outcomes included optomotor response (OMR), electroretinography (ERG), and spectral domain optical coherence tomography (SD-OCT) at 2, 4, and 6 months post-blast, and cognitive function (Y-maze) at 3 months. Spatial frequency and contrast sensitivity were reduced in ipsilateral blast-exposed eyes in both holders (p < 0.01), while contralateral eyes showed greater deficits with the enclosed holder (p < 0.05). Thinner retinas (p < 0.001) and reduced ERG a- and b- wave amplitudes (p < 0.05) were observed for both ipsilateral and contralateral eyes with the enclosed, but not the open, holder. Rats in the open holder showed cognitive deficits compared to rats in the enclosed holder (p < 0.05). Overall, the animal holder configuration used in blast exposure studies can significantly affect outcomes. Enclosed holders may cause secondary damage to the contralateral eye by concussive injury or blast wave reflection off the holder wall. Open holders may damage the brain via rapid head movement (contrecoup injury). These results highlight additional factors to be considered when evaluating patients with blast exposure or developing models of blast injury.
NSTL
Elsevier