AbstractWe examined how simulated visual field defects influence performance on a heading task to gain insight into the origins of the poorer performance seen in subjects with real visual field defects. We simulated tunnel vision and a central scotoma during ego-translation. Real-time gaze position was used to generate the appropriate optic flow pattern on the screen. The subjects’ task was to direct their gaze at the continuously changing direction of heading. Limiting the peripheral view, as in tunnel vision, or introducing a central scotoma, as in macular degeneration, affected both the accuracy with which subjects could estimate heading direction as well as the time it took them to do this. Under natural circumstances, optic flow patterns can change both smoothly, such as during pursuit of an object, and more abruptly, such as when making saccades. Therefore, we examined performance during both of these types of change. While accuracy was the same under these conditions, processing time was differentially affected. When limiting peripheral view, the influence of the field defect on processing time was larger when the heading changed abruptly than when it changed smoothly. The reverse was the case for simulated central scotomas. The influence of the defect on processing time was largest when the heading changed smoothly. Our results further point out that the calculations underlying heading detection can be performed very quickly, with processing time strongly dependent upon the speed of the simulated translation and the size of the stimulated visual area.
People with homonymous hemianopia (HH) benefit from applying compensatory scanning behaviour that limits the consequences of HH in a specific task. The aim of the study is to (i) review the current literature on task-specific scanning behaviour that improves performance and (ii) identify differences between this performance-enhancing scanning behaviour and scanning behaviour that is spontaneously adopted or acquired through training. The databases PsycInfo, Medline, and Web of Science were searched for articles on scanning behaviour in people with HH. The final sample contained 60 articles, reporting on three main tasks, i.e., search (N = 17), reading (N = 16) and mobility (N = 14), and other tasks (N = 18). Five articles reported on two different tasks. Specific scanning behaviour related to task performance in search, reading, and mobility tasks. In search and reading tasks, spontaneous adaptations differed from this performance-enhancing scanning behaviour. Training could induce adaptations in scanning behaviour, enhancing performance in these two tasks. For mobility tasks, limited to no information was found on spontaneous and training-induced adaptations to scanning behaviour. Performance-enhancing scanning behaviour is mainly task-specific. Spontaneous development of such scanning behaviour is rare. Luckily, current compensatory scanning training programs can induce such scanning behaviour, which confirms that providing scanning training is important.IMPLICATIONS FOR REHABILITATIONScanning behaviour that improves performance in people with homonymous hemianopia (HH) is task-specific.Most people with HH do not spontaneously adopt scanning behaviour that improves performance.Compensatory scanning training can induce performance-enhancing scanning behaviour. Scanning behaviour that improves performance in people with homonymous hemianopia (HH) is task-specific. Most people with HH do not spontaneously adopt scanning behaviour that improves performance. Compensatory scanning training can induce performance-enhancing scanning behaviour.
Abstract Purpose To investigate alteration of apparent fiber density (AFD), a novel diffusion MRI (dMRI) measure of white matter degeneration, in the optic nerves (ONs) of glaucoma patients. Furthermore, we aimed to study the correlation between AFD of glaucomatous ONs and peripapillary retinal never fiber layer (pRNFL) thickness and visual field mean deviation (VFMD), in order to assess the viability of AFD as a possible alternative measure for diagnosing and monitoring glaucoma. Methods Cross‐sectional study of 15 glaucoma patients and 15 healthy participants. Subjects underwent dMRI scans while being asked to close their eyes and keep eye motion to a minimum. An average population template was produced from the dMRI scans of all the subjects, and probabilistic tractography was then used to track the ONs in template space. Average track AFD was calculated for a single randomly selected ON for each subject. pRNFL thickness and VFMD measurements were acquired using optical coherence tomography and standard automated perimetry, respectively. Average AFD of glaucomatous and normal ONs were compared using ANCOVA, correcting for age as a nuisance covariate, and the correlation between average AFD of glaucomatous ONs and their corresponding pRNFL thickness and VFMD was tested using Spearman’s rank correlation test. Results Glaucomatous ONs showed a significantly lower AFD compared to healthy ONs (0.123 ± 0.034 versus 0.212 ± 0.027 a.u., respectively; p < 0.01). Average AFD of glaucomatous ONs showed a strong positive correlation with average pRNFL thickness (r = 0.863, p < 0.01) and VFMD (r = 0.850, p < 0.01). Conclusions The ONs of glaucoma patients exhibit a significant loss of AFD, which correlates strongly with both pRNFL thinning and visual field loss. Therefore, measuring ON AFD in glaucoma patients could potentially be an alternative to other established clinical measures, which could prove to be beneficial to patients who are not ideal candidates for certain clinical tests.
The authors regret that their published article is missing the following information from its funding section: The study received additional support from the "Algemene Nederlandse Vereniging ter Voorkoming van Blindheid" (www.anvvb.nl; Uitzicht grant UZ2017-27). The authors would like to apologise for any inconvenience caused. Investigating changes in axonal density and morphology of glaucomatous optic nerves using fixel-based analysisEuropean Journal of RadiologyVol. 133PreviewTo characterize neurodegeneration of glaucomatous optic nerves (ONs) in terms of changes in axonal density and morphology using fixel-based analysis (FBA), a novel framework for analyzing diffusion-weighted MRI (DWI). Furthermore, we aimed to explore the potential of FBA measures as biomarkers of glaucomatous ON degeneration. Full-Text PDF Open Access
Abstract Background and Hypothesis Approximately one-third of patients with a psychotic disorder experience visual hallucinations (VH). While new, more targeted treatment options are warranted, the pathophysiology of VH remains largely unknown. Previous studies hypothesized that VH result from impaired functioning of the vision-related networks and impaired interaction between those networks, including a possible functional disconnection between the primary visual cortex (V1) and higher-order visual processing regions. Testing these hypotheses requires sufficient data on brain activation during actual VH, but such data are extremely scarce. Study Design We therefore recruited seven participants with a psychotic disorder who were scanned in a 3 T fMRI scanner while indicating the occurrence of VH by pressing a button. Following the scan session, we interviewed participants about the VH experienced during scanning. We then used the fMRI scans to identify regions with increased or decreased activity during VH periods versus baseline (no VH). Study Results In six participants, V1 was not activated during VH, and in one participant V1 showed decreased activation. All participants reported complex VH such as human-like beings, objects and/or animals, during which higher-order visual areas and regions belonging to the vision-related networks on attention and memory were activated. Discussion These results indicate that VH are associated with diffuse involvement of the vision-related networks, with the exception of V1. We therefore propose a model for the pathophysiology of psychotic VH in which a dissociation of higher-order visual processing areas from V1 biases conscious perception away from reality and towards internally generated percepts.
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