We examined collision warning systems with different modalities and timing thresholds, assessing their impact on responses to pedestrian hazards by drivers with impaired contrast sensitivity (ICS).
...Seventeen ICS (70-84 y, median CS 1.35 log units) and 17 normal vision (NV: 68-73 y, median CS 1.95) participants completed 6 city drives in a simulator with 3 bimodal warnings: visual-auditory, visual-directional-tactile, and visual-non-directional-tactile. Each modality had one drive with early and one with late warnings, triggered at 3.5 s and 2 s time-to-collision, respectively.
ICS participants triggered more early (43 vs 37 %) and late warnings (12 vs 6 %) than NV participants and had more collisions (3 vs 0 %). Early warnings reduced time to fixate hazards (late 1.9 vs early 1.2 s, p < 0.001), brake response times (2.8 vs 1.8 s, p < 0.001) and collision rates (1.2 vs 0.02 %). With late warnings, ICS participants took 0.7 s longer to brake than NV (p < 0.001) and had an 11 % collision rate (vs 0.7 % with early warnings). Non-directional-tactile warnings yielded the lowest collision rates for ICS participants (4 vs auditory 12 vs directional-tactile 15.2 %) in late warning scenarios. All ICS participants preferred early warnings.
While early warnings improved hazard responses and reduced collisions for ICS participants, late warnings did not, resulting in high collision rates. In contrast, both early and late warnings were helpful for NV drivers. Non-directional-tactile warnings were the most effective in reducing collisions. The findings provide insights relevant to the development of hazard warnings tailored for drivers with impaired vision.
Driving is an important rehabilitation goal for patients with homonymous field defects (HFDs); however, whether or not people with HFDs should be permitted to drive is not clear. Over the last ...15-years, there has been a marked increase in the number of studies evaluating the effects of HFDs on driving performance. This review of the literature provides a much-needed summary for practitioners and researchers, addressing the following topics: regulations pertaining to driving with HFDs, self-reported driving difficulties, pass rates in on-road tests, the effects of HFDs on lane position and steering stability, the effects of HFDs on scanning and detection of potential hazards, screening for potential fitness to drive, evaluating practical fitness to drive and the efficacy of interventions to improve driving of persons with HFDs. Although there is clear evidence from on-road studies that some people with HFDs may be rated as safe to drive, others are reported to have significant deficits in skills important for safe driving, including taking a lane position too close to one side of the travel lane, unstable steering and inadequate viewing (scanning) behaviour. Driving simulator studies have provided strong evidence of a wide range in compensatory scanning abilities and detection performance, despite similar amounts of visual field loss. Conventional measurements of visual field extent (in which eye movements are not permitted) do not measure such compensatory abilities and are not predictive of on-road driving performance. Thus, there is a need to develop better tests to screen people with HFDs for visual fitness to drive. We are not yet at a point where we can predict which HFD patient is likely to be a safe driver. Therefore, it seems only fair to provide an opportunity for individualised assessments of practical fitness to drive either on the road and/or in a driving simulator.
Individuals with homonymous hemianopia (HH) are permitted to drive in some jurisdictions. They could compensate for their hemifield vision loss by scanning toward the blind side. However, some ...drivers with HH do not scan adequately well to the blind side when approaching an intersection, resulting in delayed responses to hazards.
To evaluate whether auditory reminder cues promoted proactive scanning on approach to intersections.
This cross-sectional, single-visit driving simulator study was conducted from October 2018 to May 2019 at a vision rehabilitation research laboratory. A volunteer sample of individuals with HH without visual neglect are included in this analysis. This post hoc analysis was completed in July and August 2020.
Participants completed drives with and without scanning reminder cues (a single tone from a speaker on the blind side). Scanning was quantified by the percentage of intersections at which an early large scan was made (a scan with a head movement of at least 20° made before 30 m from the intersection). Responses to motorcycle hazards at intersections were quantified by the time to the first fixation and the time to the horn-press response.
Sixteen individuals were recruited and completed the study. Two were subsequently excluded from analyses. Thus, data from 14 participants (median IQR age, 54 36-66 years; 13 men 93%) were included. Stroke was the primary cause of the HH (10 participants 71%). Six (43%) had right-sided HH. Participants were more likely to make an early large scan to the blind side in drives with vs without cues (65% vs 45%; difference, 20% 95% CI, 5%-37%; P < .001). When participants made an early large scan to the blind side, they were faster to make their first fixation on blind-side motorcycles (mean SD, 1.77 1.34 vs 3.88 1.17 seconds; difference, -2.11 95% CI, -2.46 to -1.75 seconds; P < .001) and faster to press the horn (mean SD, 2.54 1.19 vs 4.54 1.37 seconds; difference, -2.00 95% CI, -2.38 to -1.62 seconds; P < .001) than when they did not make an early scan.
This post hoc analysis suggests that auditory reminder cues may promote proactive scanning, which may be associated with faster responses to hazards. This hypothesis should be considered in future prospective studies.
There is a major lack of randomized controlled clinical trials evaluating the efficacy of prismatic treatments for hemianopia. Evidence for their effectiveness is mostly based on anecdotal case ...reports and open-label evaluations without a control condition.
To evaluate the efficacy of real relative to sham peripheral prism glasses for patients with complete homonymous hemianopia.
Double-masked, randomized crossover trial at 13 study sites, including the Peli laboratory at Schepens Eye Research Institute, 11 vision rehabilitation clinics in the United States, and 1 in the United Kingdom. Patients were 18 years or older with complete homonymous hemianopia for at least 3 months and without visual neglect or significant cognitive decline.
Patients were allocated by minimization into 2 groups. One group received real (57-prism diopter) oblique and sham (<5-prism diopter) horizontal prisms; the other received real horizontal and sham oblique, in counterbalanced order. Each crossover period was 4 weeks.
The primary outcome was the overall difference, across the 2 periods of the crossover, between the proportion of participants who wanted to continue with (said yes to) real prisms and the proportion who said yes to sham prisms. The secondary outcome was the difference in perceived mobility improvement between real and sham prisms.
Of 73 patients randomized, 61 completed the crossover. A significantly higher proportion said yes to real than sham prisms (64% vs 36%; odds ratio, 5.3; 95% CI, 1.8-21.0). Participants who continued wear after 6 months reported greater improvement in mobility with real than sham prisms at crossover end (P = .002); participants who discontinued wear reported no difference.
Real peripheral prism glasses were more helpful for obstacle avoidance when walking than sham glasses, with no differences between the horizontal and oblique designs. Peripheral prism glasses provide a simple and inexpensive mobility rehabilitation intervention for hemianopia.
clinicaltrials.gov Identifier: NCT00494676.
Assisted and autonomous driving technologies may be a new paradigm shift for the driving rehabilitation field to enable less restricted driving, increase driving confidence, and maintain driving ...safety for drivers with vision impairment.
This study aimed to document how a driver with vision impairment uses assistance and automation systems in a Tesla car based on real-world experiences of using these technologies.
A 53-year-old man with Stargardt disease and 20/182 visual acuity self-explored the use of driver assistance technologies, which resulted in purchasing a Tesla Model Y with the full self-driving package in 2020. Two semistructured interviews were administered to quantify the driver's driving habits, adaptive strategies, use of the assisted and semiautonomous driving features in the Tesla car, and use of his bioptic telescope.
When driving a Tesla car, the patient developed new driving strategies by codriving with different assisted and semiautonomous functions (e.g., Traffic-Aware Cruise Control, Traffic Light and Stop Sign Control, Autopilot) in different road environments. He shifted his main task from active driving to supervising the car automation systems in most driving situations. He also integrated a new use of his bioptic telescope to support him with monitoring the road environment before granting permission to the automated systems for car maneuver changes. The patient reported that driving confidence greatly increased and that he is able to drive more often and in situations that he would otherwise avoid because of difficulties related to his vision.
This clinical report demonstrates how assisted and semiautonomous driving systems in a Tesla car were used to support daily driving by a driver with vision impairment. Codriving with these systems allows him to confidently drive more often and to avoid less situations than he used to.
It is currently still unknown why some drivers with visual field loss can compensate well for their visual impairment while others adopt ineffective strategies. This paper contributes to the ...methodological investigation of the associated top-down mechanisms and aims at validating a theoretical model on the requirements for successful compensation among drivers with homonymous visual field loss.
A driving simulator study was conducted with eight participants with homonymous visual field loss and eight participants with normal vision. Participants drove through an urban surrounding and experienced a baseline scenario and scenarios with visual precursors indicating increased likelihoods of crossing hazards. Novel measures for the assessment of the mental model of their visual abilities, the mental model of the driving scene and the perceived attention demand were developed and used to investigate the top-down mechanisms behind attention allocation and hazard avoidance.
Participants with an overestimation of their visual field size tended to prioritize their seeing side over their blind side both in subjective and objective measures. The mental model of the driving scene showed close relations to the subjective and actual attention allocation. While participants with homonymous visual field loss were less anticipatory in their usage of the visual precursors and showed poorer performances compared to participants with normal vision, the results indicate a stronger reliance on top-down mechanism for drivers with visual impairments. A subjective focus on the seeing side or on near peripheries more frequently led to bad performances in terms of collisions with crossing cyclists.
The study yielded promising indicators for the potential of novel measures to elucidate top-down mechanisms in drivers with homonymous visual field loss. Furthermore, the results largely support the model of requirements for successful compensatory scanning. The findings highlight the importance of individualized interventions and driver assistance systems tailored to address these mechanisms.
Objective
We conducted a driving simulator study to investigate scanning and hazard detection before entering an intersection.
Background
Insufficient scanning has been suggested as a factor ...contributing to intersection crashes. However, little is known about the relative importance of the head and eye movement components of that scanning in peripheral hazard detection.
Methods
Eleven older (mean 67 years) and 18 younger (mean 27 years) current drivers drove in a simulator while their head and eye movements were tracked. They completed two city drives (42 intersections per drive) with motorcycle hazards appearing at 16 four-way intersections per drive.
Results
Older subjects missed more hazards (10.2% vs. 5.2%). Failing to make a scan with a substantial head movement was the primary reason for missed hazards. When hazards were detected, older drivers had longer RTs (2.6s vs. 2.3s), but drove more slowly; thus, safe response rates did not differ between the two groups (older 83%; younger 82%). Safe responses were associated with larger (28.8° vs. 20.6°) and more numerous (9.4 vs. 6.6) gaze scans. Scans containing a head movement were stronger predictors of safe responses than scans containing only eye movements.
Conclusion
Our results highlight the importance of making large scans with a substantial head movement before entering an intersection. Eye-only scans played little role in detection and safe responses to peripheral hazards.
Application
Driver training programs should address the importance of making large scans with a substantial head movement before entering an intersection.
There is scant rigorous evidence about the real-world mobility benefit of electronic mobility aids.
To evaluate the effect of a collision warning device on the number of contacts experienced by blind ...and visually impaired people in their daily mobility.
In this double-masked randomized clinical trial, participants used a collision warning device during their daily mobility over a period of 4 weeks. A volunteer sample of 31 independently mobile individuals with severe visual impairments, including total blindness and peripheral visual field restrictions, who used a long cane or guide dog as their habitual mobility aid completed the study. The study was conducted from January 2018 to December 2019.
The device automatically detected collision hazards using a chest-mounted video camera. It randomly switched between 2 modes: active mode (intervention condition), where it provided alerts for detected collision threats via 2 vibrotactile wristbands, and silent mode (control condition), where the device still detected collisions but did not provide any warnings to the user. Scene videos along with the collision warning information were recorded by the device. Potential collisions detected by the device were reviewed and scored, including contacts with the hazards, by 2 independent reviewers. Participants and reviewers were masked to the device operation mode.
Rate of contacts per 100 hazards per hour, compared between the 2 device modes within each participant. Modified intention-to-treat analysis was used.
Of the 31 included participants, 18 (58%) were male, and the median (range) age was 61 (25-73) years. A total of 19 participants (61%) had a visual acuity (VA) of light perception or worse, and 28 (90%) reported a long cane as their habitual mobility aid. The median (interquartile range) number of contacts was lower in the active mode compared with silent mode (9.3 6.6-14.9 vs 13.8 6.9-24.3; difference, 4.5; 95% CI, 1.5-10.7; P < .001). Controlling for demographic characteristics, presence of VA better than light perception, and fall history, the rate of contacts significantly reduced in the active mode compared with the silent mode (β = 0.63; 95% CI, 0.54-0.73; P < .001).
In this study involving 31 visually impaired participants, the collision warnings were associated with a reduced rate of contacts with obstacles in daily mobility, indicating the potential of the device to augment habitual mobility aids.
ClinicalTrials.gov Identifier: NCT03057496.
We conducted a driving simulator study to investigate the effects of monitoring intersection cross traffic on gaze behaviors and responses to pedestrians by drivers with hemianopic field loss (HFL).
...Sixteen HFL and sixteen normal vision (NV) participants completed two drives in an urban environment. At 30 intersections, a pedestrian ran across the road when the participant entered the intersection, requiring a braking response to avoid a collision. Intersections with these pedestrian events had either (1) no cross traffic, (2) one approaching car from the side opposite the pedestrian location, or (3) two approaching cars, one from each side at the same time.
Overall, HFL drivers made more (
< 0.001) and larger (
= 0.016) blind- than seeing-side scans and looked at the majority (>80%) of cross-traffic on both the blind and seeing sides. They made more numerous and larger gaze scans (
< 0.001) when they fixated cars on both sides (compared to one or no cars) and had lower rates of unsafe responses to blind- but not seeing-side pedestrians (interaction,
= 0.037). They were more likely to demonstrate compensatory blind-side fixation behaviors (faster time to fixate and longer fixation durations) when there was no car on the seeing side. Fixation behaviors and unsafe response rates were most similar to those of NV drivers when cars were fixated on both sides.
For HFL participants, making more scans, larger scans and safer responses to pedestrians crossing from the blind side were associated with looking at cross traffic from both directions. Thus, cross traffic might serve as a reminder to scan and provide a reference point to guide blind-side scanning of drivers with HFL. Proactively checking for cross-traffic cars from both sides could be an important safety practice for drivers with HFL.
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