154 research outputs found
Despite impaired binocular function, binocular disparity integration across the visual field is spared in normal aging and glaucoma
No full textPurpose: to examine how binocularly asymmetric glaucomatous visual field damage affects binocular disparity processing across the visual field.Methods: we recruited 18 patients with primary open-angle glaucoma, 16 age-matched controls, and 13 young controls. Participants underwent standard clinical assessments of binocular visual acuity, binocular contrast sensitivity, stereoacuity, and perimetry. We employed a previously validated psychophysical procedure to measure how sensitivity to binocular disparity varied across spatial frequencies and visual field sectors (i.e., with full-field stimuli spanning the central 21° of the visual field and with stimuli restricted to annular regions spanning 0°–3°, 3°–9°, or 9°–21°). We employed measurements with annular stimuli to model different possible scenarios regarding how disparity information is combined across visual field sectors. We adjudicated between potential mechanisms by comparing model predictions to the patterns observed with full-field stimuli.Results: perimetry confirmed that patients with glaucoma exhibited binocularly asymmetric visual field damage (P < 0.001). Across participant groups, foveal regions preferentially processed disparities at finer spatial scales, whereas periphery regions were tuned for coarser scales (P < 0.001). Disparity sensitivity also decreased from fovea to periphery (P < 0.001) and across participant groups (Ps < 0.01). Finally, similar to controls, patients with glaucoma exhibited near-optimal disparity integration, specifically at low spatial frequencies (P < 0.001). Conclusions: contrary to the conventional view that glaucoma spares central vision, we find that glaucomatous damage causes a widespread loss of disparity sensitivity across both foveal and peripheral regions. Despite these losses, cortical integration mechanisms appear to be well preserved, suggesting that patients with glaucoma make the best possible use of their remaining binocular function.</p
Nanoscale spin-state ordering in LaCoO3 epitaxial thin films
No full textThe nature of magnetic ordering in LaCoO3 epitaxial thin films has been the subject of considerable debate. We present direct observations of the spin-state modulation of Co ions in LaCoO3 epitaxial thin films on an atomic scale using aberration-corrected scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS), and ab initio calculations based on density functional theory (DFT) calculations. The results of an atomic-resolution STEM/EELS study indicate that the superstructure is not associated with oxygen vacancies; rather, it is associated with a higher spin state of Co3+ ions and their ordering. DFT calculations successfully reproduced the modulation of lattice spacing with the introduction of spin ordering. This result identifies the origins of intrinsic phenomena in strained LaCoO3 and provides fundamental clues for understanding ferromagnetism in Co-based oxides.129301sciescopu
MNREAD Baseline Data for Normal Vision Across the Lifespan
No full textContains MNREAD estimates for 654 participants with normal vision (age range 8-81). The four MNREAD estimates are : Maximum Reading Speed, Reading Accessibility Index, Critical Print Size, Reading Acuity.The continuous-text reading-acuity test MNREAD is designed to measure the reading performance of people with normal and low vision. This test is used to estimate maximum reading speed (MRS), critical print size (CPS), reading acuity (RA), and the reading accessibility index (ACC).
The present data contains MNREAD data from 645 normally sighted participants ranging in age from 8 to 81 years. The data were collected in several studies conducted by different testers and at different sites in our research program, enabling evaluation of robustness of the test.
The data allows to: 1) study the age dependence of reading performance for normally sighted individuals; 2) provide baseline data for MNREAD testing.Research supported by NIH grant EY002934Calabrèse, Aurélie; Cheong, Allen M. Y.; Cheung, Sing-Hang; He, Yingchen; Kwon, MiYoung; Mansfield, J. Stephen; Subramanian, Ahalya; Yu, Deyue; Legge, Gordon E.. (2017). MNREAD Baseline Data for Normal Vision Across the Lifespan. Retrieved from the University Digital Conservancy, https://doi.org/10.13020/D6Q08Z
Spatial-frequency bandwidth requirements for pattern vision.
No full textUniversity of Minnesota Ph.D. dissertation. July 2010. Major: Psychology. Advisor: Gordon E. Legge. 1 computer file (PDF); xiii, 125 pages, appendices A-J. Ill. (some col.)Visual resolution is an important factor which affects human pattern recognition. Dealing with degraded visual resolution is relevant to both normally sighted and visually impaired individuals. This thesis describes three studies that address human pattern recognition under conditions of low resolution and its linkage to real life visual activities such as reading.
Deficiencies of pattern recognition in peripheral vision might result in higher bandwidth requirements, and may contribute to the functional problems of people with central-field loss. In the first study (Chapter 2), we asked whether there are differences in spatial-frequency requirements between central and peripheral vision for pattern recognition. Critical bandwidths (i.e., the minimum low-pass filter bandwidth yielding 80% recognition accuracy) were measured for letter and face recognition. We found that critical bandwidths increased from central to peripheral vision for both letter and face recognition, demonstrating that peripheral vision requires higher bandwidth for pattern recognition than central vision.
In the second study (Chapter 3), we asked how letter recognition is possible with severe reduction in the spatial resolution of letters. We addressed the question by testing the hypothesis that when spatial resolution is severely limited, the visual system relies increasingly on contrast coding for letter recognition. The size of the gap between contrast thresholds for detecting and recognizing letters was used as a marker for the extent of reliance for contrast coding. We found that as spatial resolution for rendering letters decreases, the system relies more on contrast differences.
Letters are the fundamental building blocks of text. Besides single letter recognition, it has been proposed that the visual span, the number of letters that can be recognized without moving the eyes, imposes a limitation on reading speed. In the third study (Chapter 4), we investigated whether the bandwidth requirement for reading speed can be accounted for by the bandwidth requirement for letter recognition. We found that bandwidth limitations on reading performance appear to be closely associated with bandwidth limitations on the visual span, and also to a bandwidth limitation on letter recognition.
Together, these three studies provide us with a better understanding of spatial-frequency requirements for pattern vision.Kwon, MiYoung. (2010). Spatial-frequency bandwidth requirements for pattern vision.. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/94982
Correlative study between the local atomic and electronic structures of amorphous carbon materials via 4D-STEM and STEM-EELS
No full text© 2022 Author(s).Amorphous materials have been used in a range of electronic and photonic applications, and the need for quantitative analytical techniques on their local structural information is growing. We present a comprehensive analysis of the atomic and electronic structures of an amorphous material, amorphous carbon (a-C), with scanning transmission electron microscopy (STEM)-derived techniques, four-dimensional STEM (4D-STEM), and STEM-electron energy loss spectroscopy (STEM-EELS). Each diffraction pattern of an a-C layer stack acquired via 4D-STEM is transformed into a reduced density function (RDF) and a radial variance profile (RVP) to retrieve the information on the atomic structures. Importantly, a machine-learning approach (preferably cluster analysis) separates distinct features in the EELS and RDF datasets; it also describes the spatial distributions of these features in the scanned regions. Consequently, we showed that the differences in the sp2/sp3 ratio and the involvement of additional elements led to changes in the bond length. Furthermore, we identified the dominant types of medium-range ordering structures (diamond-like or graphite-like nano-crystals) by correlations among the EELS, RDF, and RVP data. The information obtained via STEM-EELS and 4D-STEM can be strongly correlated, leading to the comprehensive characterization of the a-C layer stack for a nanometer-scale area. This process can be used to investigate any amorphous material, thereby yielding comprehensive information regarding the origins of notable properties.N
Effects of paramagnetic fluctuations on the thermochemistry of MnO (100) surfaces in the oxygen evolution reaction
No full textWe investigated the effects of paramagnetic (PM) fluctuations on the
thermochemistry of the MnO(100) surface in the oxygen evolution reaction (OER)
using the "noncollinear magnetic sampling method \textit{plus} "
(NCMSM). Various physical properties, such as the electronic structure,
free energy, and charge occupation, of the MnO (100) surface in the PM state
with several OER intermediates, were reckoned and compared to those in the
antiferromagnetic (AFM) state. We found that PM fluctuation enhances charge
transfer from a surface Mn ion to each of the intermediates and strengthens the
chemical bond between them, while not altering the overall features, such as
the rate determining step and resting state, in reaction pathways. The enhanced
charge transfer can be attributed to the delocalized nature of valence bands
observed in the PM surface. In addition, it was observed that chemical-bond
enhancement depends on the intermediates, resulting in significant deviations
in reaction energy barriers. Our study suggests that PM fluctuations play a
significant role in the thermochemistry of chemical reactions occurring on
correlated oxide surfaces.Comment: Maintext: 15 pages, 3 figures 2 tables; SI: 3 pages, 2 figure
Spin-orbit coupling driven orbital-selective doping effect in Sr2Ru1-xIrxO4
No full textOrbital-selective phenomena in mutliorbital systems have received much attention due to their uniqueness as well as possible connections to other phenomena. As orbital-selectiveness is mostly related to the crystal structure, finding a new control parameter other than structure would be of significant importance. Here we report discovery of an orbital-selective doping effect in Sr2Ru1-xIrxO4 (SRIO). Our systematic electronic structure study of SRIO reveals an anomalous orbital-selective doping effect and concomitant Lifshitz transitions (LTs) in the gamma band. With the help of a tight-binding calculation, we find that the orbital-selective doping effect is due to variation in the spin-orbit coupling (SOC) strength. Our findings not only elucidate the mechanism of LTs in the gamma band in SRIO but may also open new avenues for novel SOC-controlled orbital-selective phenomena.11Nsciescopu
Understanding luminescence properties of grain boundaries in GaN thin films and their atomistic origin
No full textWe report our findings on the optical properties of grain boundaries in GaN films grown on graphene layers and discuss their atomistic origin. We combine electron backscatter diffraction with cathodoluminescence to directly correlate the structural defects with their optical properties, enabling the high-precision local luminescence measurement of the grain boundaries in GaN films. To further understand the atomistic origin of the luminescence properties, we carefully probed atomic core structures of the grain boundaries by exploiting aberration-corrected scanning transmission electron microscopy. The atomic core structures of grain boundaries show different ordering behaviors compared with those observed previously in threading dislocations. Energetics of the grain boundary core structures and their correlation with electronic structures were studied by first principles calculation. Published by AIP Publishing
Three-dimensional binocular eye–hand coordination in normal vision and with simulated visual impairment
No full textSensorimotor coupling in healthy humans is demonstrated by the higher accuracy of visually tracking intrinsically—rather than extrinsically—generated hand movements in the fronto-parallel plane. It is unknown whether this coupling also facilitates vergence eye movements for tracking objects in depth, or can overcome symmetric or asymmetric binocular visual impairments. Human observers were therefore asked to track with their gaze a target moving horizontally or in depth. The movement of the target was either directly controlled by the observer’s hand or followed hand movements executed by the observer in a previous trial. Visual impairments were simulated by blurring stimuli independently in each eye. Accuracy was higher for self-generated movements in all conditions, demonstrating that motor signals are employed by the oculomotor system to improve the accuracy of vergence as well as horizontal eye movements. Asymmetric monocular blur affected horizontal tracking less than symmetric binocular blur, but impaired tracking in depth as much as binocular blur. There was a critical blur level up to which pursuit and vergence eye movements maintained tracking accuracy independent of blur level. Hand–eye coordination may therefore help compensate for functional deficits associated with eye disease and may be employed to augment visual impairment rehabilitation.</p
Association between glaucoma and at–fault motor vehicle collision involvement among older drivers
No full textObjective\ud
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To examine the association between glaucoma and motor vehicle collision (MVC) involvement among older drivers, including the role of visual field impairment that may underlie any association found.\ud
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Design\ud
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A retrospective population-based study\ud
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Participants\ud
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A sample of 2,000 licensed drivers aged 70 years and older who reside in north central Alabama.\ud
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Methods\ud
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At-fault MVC involvement for five years prior to enrollment was obtained from state records. Three aspects of visual function were measured: habitual binocular distance visual acuity, binocular contrast sensitivity and the binocular driving visual field constructed from combining the monocular visual fields of each eye. Poisson regression was used to calculate crude and adjusted rate ratios (RR) and 95% confidence intervals (CI).\ud
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Main Outcomes Measures\ud
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At-fault MVC involvement for five years prior to enrollment. \ud
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Results\ud
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Drivers with glaucoma (n = 206) had a 1.65 (95% confidence interval [CI] 1.20-2.28, p = 0.002) times higher MVC rate compared to those without glaucoma after adjusting for age, gender and mental status. Among those with glaucoma, drivers with severe visual field loss had higher MVC rates (RR = 2.11, 95% CI 1.09-4.09, p = 0.027), whereas no significant association was found among those with impaired visual acuity and contrast sensitivity. When the visual field was sub-divided into six regions (upper, lower, left, and right visual fields; horizontal and vertical meridians), we found that impairment in the left, upper or lower visual field was associated with higher MVC rates, and an impaired left visual field showed the highest RR (RR = 3.16, p = 0.001) compared to other regions. However, no significant association was found in deficits in the right side or along the horizontal or vertical meridian.\ud
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Conclusions\ud
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A population-based study suggests that older drivers with glaucoma are more likely to have a history of at-fault MVC involvement than those without glaucoma. Impairment in the driving visual field in drivers with glaucoma appears to have an independent association with at-fault MVC involvement, whereas visual acuity and contrast sensitivity impairments do not
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