Frans W. Cornelissen

Purpose: Acquired brain injury (ABI) may cause homonymous visual field (VF) defects. Standard automated perimetry (SAP) is the gold standard for VF assessment, but it can be challenging in ABI. Continuous visual stimulus tracking (SONDA; Standardised Oculomotor and Neurological Disorders Assessment) simplifies the perimetric task to following a moving stimulus on a screen. We investigated whether tracking performance (agreement between gaze and stimulus position) measured with a SONDA‐based eye movement perimetry technique (SONDA‐EMP) (1) can detect visual function loss in patients with homonymous VF defects, (2) can quantify visual function loss (in terms of SAP Mean Sensitivity [MS]) and (3) shows a learning effect. Methods: Tracking performance was evaluated in 16 cases with unilateral ABI (median [IQR] age 66 [62–68] years; SAP MS 19 [15–21] dB; 8/8 with left‐/right‐sided VF defect) and compared to previously collected data of 36 controls (age 70 [67–72] years). All participants monocularly tracked a moving stimulus (Goldmann size III) at three Weber contrasts (40%, 160% and 640%), while their eye movements were recorded. Results: ABI significantly decreased tracking performance ( p < 0.0001) compared to controls at all contrasts, independently of VF defect side ( p = 0.53). Performance improved from 40% to 160% contrast ( p < 0.0001), but not from 160% to 640% ( p = 0.53). SAP MS correlated moderately to strongly with tracking performance ( r = 0.46 [ p = 0.07], 0.73 [ p = 0.01], 0.67 [ p = 0.004], for 40%, 160% and 640% contrast, respectively). Retesting showed no significant learning effect. Conclusion: SONDA‐EMP can detect visual function loss from ABI. The reduction in tracking performance depends on the amount of VF loss.

Purpose: Standard automated perimetry (SAP) is the gold standard for functional assessment in glaucoma. SAP can be too demanding for some groups of patients. Continuous visual stimulus tracking (SONDA: Standardized Oculomotor and Neurological Disorders Assessment) simplifies the perimetric task to following a moving stimulus on a screen. In this study we evaluated the screening performance of SONDA-based eye movement perimetry (SONDA-EMP) in glaucoma. To explore generalizability, we evaluated an experimental setup (SONDA-Eyelink) and a clinic-ready version (SONDA-Neon). Methods: SONDA-Eyelink and SONDA-Neon measurements were performed in 100 cases with glaucoma (36, 36, and 28 with early, moderate, and severe glaucoma, respectively) and 100 age-similar controls. Participants monocularly tracked a moving stimulus (Goldmann size III) at 40% contrast (both setups) and 160% (SONDA-Eyelink). Eye movements were continuously recorded. Outcome was the agreement between gaze and stimulus position. We used previously collected glaucoma case-control data to build a continuous ‘glaucoma screening score’. This score was used for an ROC-analysis applied to the current, independently collected dataset. We predefined good screening performance as: at 95% specificity, a sensitivity of at least 50%, 90%, and 100% for early, moderate, and severe glaucoma, respectively. Results: At 95% specificity, the sensitivity of SONDA-Eyelink was 58, 94, and 100% at 40% contrast and 56, 97, and 100% at 160% contrast for early, moderate, and severe glaucoma, respectively. Sensitivity was 53, 94, and 100% for SONDA-Neon. Conclusions: SONDA-EMP is a novel, fast, and intuitive method to screen for visual function loss in glaucoma.

Individuals with homonymous hemianopia (HH) may benefit from adopting compensatory crossing and scanning strategies to successfully cross streets. In this study, we explored the effect of HH on street crossing outcomes, crossing behavior and scanning behavior in a virtual environment. Individuals with real HH (N = 18), unimpaired vision (N = 18), and simulated HH (N = 18) crossed a virtual street displayed through a head-mounted display. Virtual cars approached from both directions, traveling at a speed of either 30 or 50 km/h. Participants' crossing and scanning behaviors were recorded and analyzed across groups and the two car speeds. Although individuals with real and simulated HH took more time to cross compared to individuals with unimpaired vision depending on the car speed, the number of collisions and time-to-contact after crossings did not differ between groups. We observed no differences in the selection of car gaps, crossing initiation, and scanning behavior between groups. Our findings suggest that individuals with real and simulated HH align their crossing behavior to their visuomotor capabilities by using varying compensatory strategies. HH did not alter scanning behavior before crossing a virtual street. Despite its current shortcomings, virtual reality holds promise for street crossing research and rehabilitation.

Visual crowding refers to the difficulty in recognizing objects in the periphery when surrounded by clutter. Traditional trial-based paradigms, while effective in measuring spatial aspects of crowding, do not capture the temporal dynamics involved. In this study, we assessed the feasibility of a continuous psychophysics paradigm that measures both the spatial extent and temporal processes of visual crowding. Eight participants continuously tracked the orientation of a rotating Landolt C while the distance between the target and a ring-shaped flanker varied systematically over time. Participants set a reference stimulus to match the orientation of the target. The paradigm included “jump-points,” where the orientation of the target suddenly shifted, allowing us to measure the recovery rate of participants’ tracking errors following these disruptions. Tracking accuracy was compared between flanked and isolated conditions. Additionally, participants’ report errors were used to assess both the crowding extent and the temporal recovery rate from the jumps, with the crowding extent results compared with those obtained from a conventional trial-based version of the paradigm. The recovery rate was calculated by fitting an exponential decay function to participants’ report errors after the jumps. The results showed that the crowding extent measured using the continuous paradigm was consistent with that obtained using trial-based methods and aligned with Bouma's rule. Moreover, flankers decreased both tracking accuracy and recovery rate following the jumps. These results demonstrate that our continuous psychophysics paradigm is useful for measuring the spatiotemporal aspects of crowding.

Introduction: Virtual reality environments presented through head mounted displays (HMDs) hold promise for training or studying mobility activities, such as cycling, walking, and street crossing. Yet, the limited field of view (FoV) of HMDs may influence scanning behaviour, reducing the translatability of findings to real-life situations. This study aims to (i) investigate how a reduced FoV influences scanning behaviour during mobility activities, and (ii) whether these alterations in scanning vary across these activities. Method: Sixteen participants performed a real-life walking, cycling and street crossing activity twice; once with and once without a reduced FoV. A mobile eye-tracker with a built in gyroscope recorded scanning behaviour. Scanning behaviour was evaluated in terms of saccadic frequency and amplitude, horizontal head movement frequency and amplitude, and the horizontal and vertical eye position. Results: The participants performed more horizontal head movements with larger amplitudes during the reduced FoV compared to the normal FoV. Additionally, they distributed their horizontal eye position more towards the central regions and less towards their peripheral regions. Overall, the range of both horizontal and vertical eye position decreased. The impact of the reduced FoV on horizontal head movement amplitude, horizontal eye position, and vertical eye position varied across activities. Conclusion: Generally, individuals seem to compensate for a reduced FoV by making more horizontal head movements with large amplitudes, while reducing the eye position distribution. Consequently, caution is advised when translating outcomes on scanning behaviour observed in HMDs to those expected in real-life situations.

PURPOSE: Primary open angle glaucoma (POAG, hereafter referred to as glaucoma) is a neuro-ophthalmic disease characterized by progressive degeneration of the retinal ganglion cells and nerve fibers. However, the exact pathogenesis of this disease remains unresolved, notably including its effect on the neural circuits of the visual pathway and cortex. METHODS: We used both resting state (RS) and stimulus-driven functional MRI and applied a novel analysis technique (Bayesian Connective Field Modelling) to investigate the intra-cortical functional connective organization of the early visual cortex of patients with POAG. Analogous to population receptive field modelling for stimulus-driven activity, our connective field approach models how the activity in one cortical area (e.g. V2) can be explained based on that of another (e.g. V1). RESULTS: We compared the CF parameters obtained for the early visual cortical areas in glaucoma to those of control participants. Our results show that in both RS and stimulus-driven conditions, CF sizes in early visual areas are smaller in glaucoma compared to control participants. To assess if these differences could be related to the ocular damage altering the visual input to the visual cortex, the control participants also observed the visual stimuli with a simulated scotoma (SS), designed to match the visual sensitivity of a participant affected by glaucoma as assessed using standard automated perimetry (SAP). In this condition, no differences in CF size were observed. Moreover, we found that CF size did not correlate with glaucoma severity, as assessed using both SAP and optical coherence tomography (OCT). CONCLUSION: The observed differences in CF metrics may be the result of local reorganization or neurodegeneration of the early visual cortex that must have developed already at an early disease stage.

Objective: We present a novel framework for the detection and continuous evaluation of 3D motion perception by deploying a virtual reality environment with built-in eye tracking. Methods: We created a biologically-motivated virtual scene that involved a ball moving in a restricted Gaussian random walk against a background of 1/f noise. Sixteen visually healthy participants were asked to follow the moving ball while their eye movements were monitored binocularly using the eye tracker. We calculated the convergence positions of their gaze in 3D using their fronto-parallel coordinates and linear least-squares optimization. Subsequently, to quantify 3D pursuit performance, we employed a first-order linear kernel analysis known as the Eye Movement Correlogram technique to separately analyze the horizontal, vertical and depth components of the eye movements. Finally, we checked the robustness of our method by adding systematic and variable noise to the gaze directions and re-evaluating 3D pursuit performance. Results: We found that the pursuit performance in the motion-through depth component was reduced significantly compared to that for fronto-parallel motion components. We found that our technique was robust in evaluating 3D motion perception, even when systematic and variable noise was added to the gaze directions. Conclusion: The proposed framework enables the assessment of 3D Motion perception by evaluating continuous pursuit performance through eye-tracking. Significance: Our framework paves the way for a rapid, standardized and intuitive assessment of 3D motion perception in patients with various eye disorders.

Psychosis is frequently associated with the occurrence of visual hallucinations (VH), but their etiology remains largely unknown. While patients with psychosis show deficits on various behavioral visual and attentional tasks, previous studies have not specifically related these deficits to the presence of VH. This suggests that tasks used in these studies do not target the visual-cognitive neural mechanisms that mediate VH, which in turn limits the development of effective therapies. We therefore designed a study to target these mechanisms directly. In this case control study we asked patients with psychosis who had previously experienced VH to indicate when they recognized objects that were gradually emerging from dynamic visual noise, while scanning their brains using functional Magnetic Resonance Imaging. In a previous study, this recognition task was used to identify the neural basis of VH in patients with Parkinson’s Disease. Based on this earlier work, we decided to test the following hypothesis: when compared to psychosis patients not experiencing VH and age-matched healthy controls, psychosis patients with VH show reduced occipital activity and frontal activity around the moment of recognition (known as pop-out). For all groups, neuroimaging revealed increased activity in all examined visual areas around pop-out. However, psychosis patients with VH showed reduced occipital responsiveness, especially in the inferior part of the bilateral lateral occipital complex, a region known to play a key role in object recognition. We did not observe altered frontal or prefrontal activity before pop-out in this group. A possible explanation is that the relatively sustained activation of the visual memory-related angular gyri around pop-out may have compensated for the impaired early visual processing in psychosis patients with VH. We discuss our results in terms of current theories of visual hallucinations, such as predictive coding and contextual modulation. Our study is the first to show that visual processing deficits contribute to the occurrence of VH in psychosis. These findings could be used to develop tests to identify the visual-cognitive mechanisms that mediate VH in this group.

Background: more than one-third of patients with psychosis experience visual hallucinations, but the underlying pathomechanism remains largely unknown. Although schizophrenia is related to altered brain functional connectivity, it is unknown how this could predispose patients to experience visual hallucinations. Previous work suggested that this predisposition is caused by alterations in vision-related networks, including the Visual Network, possibly with a specific focus on the Ventral Attention Network ¹ . This network responds to salient stimuli from the Visual Network and operates as a switch between the internally-focused Default Mode Network and the outside-world-focused Dorsal Attention Network. Methods: in this case control study we investigated the role of these networks in three groups: 14 participants with a psychotic disorder and visual hallucinations, 15 participants with a psychotic disorder without visual hallucinations, and 16 healthy controls. All patients underwent resting state functional Magnetic Resonance Imaging after which we determined the intra- and inter-network functional connectivity of these networks in all participants. We also used fast Eigenvector Centrality Mapping to determine the most central regions, i.e. the most functionally communicating regions, within these networks. Results: compared to healthy controls, patients with visual hallucinations had lower functional connectivity, both intra-network and inter-network, in all vision-related networks. This decrease was most prominent for the Ventral Attention Network and the Dorsal Attention Network for intra-network functional connectivity. Moreover, Eigenvector Centrality Mapping showed a severe decrease in functional communication within the Visual Network in the right intracalcarine sulcus, with a simultaneous increase in functional communication in the lateral part of the left middle occipital gyrus, a region involved in object recognition. The results of patients without hallucinations were generally in between patients with visual hallucinations and healthy controls. Discussion: our study shows that widespread dysconnectivity of predominantly vision-related functional networks may predispose patients with psychosis to generate visual hallucinations. These results are in line with previous models of hallucinations in psychosis which suggested that the processing deficits in the Visual Network may cause or exacerbate inadequate co-functioning and switching between the Default Mode Network and the Dorsal Attentional Network, possibly due to impaired Ventral Attention Network functioning. In combination with impaired attending of visual signals by the Dorsal Attentional Network, this may lead to inappropriate saliency processing and wrongly attributing an external origin to internally generated events and, consequently, to visual hallucinations. The often complex nature of psychotic visual hallucinations may be explained by the more central role of object processing regions.