Aaron J. Mandel

Driving With Hemianopia, I: Detection Performance in a Driving Simulator

PURPOSE This study was designed to examine the effect of homonymous hemianopia (HH) on detection of pedestrian figures in multiple realistic and hazardous situations within the controlled environment of a driving simulator. METHODS Twelve people with complete HH and without visual neglect or cognitive decline and 12 matched (age, sex, and years of driving experience) normally sighted (NV) drivers participated. They drove predetermined city and rural highway routes (total, 120 minutes) during which pedestrian figures appeared at random intervals along the roadway (R-Peds; n = 144) and at intersections (I-Peds; n = 10). Detection rates and response times were derived from participant horn presses. RESULTS Drivers with HH exhibited significantly (P < 0.001) lower R-Ped detection rates on the blind side than did NV drivers (range, 6%-100%). Detection of I-Peds on the blind side was also poor (8%-55%). Age and blind-side detection rates correlated negatively (Spearman r = -0.71, P = 0.009). Although blind-side response times of drivers with HH were significantly (P < 0.001) longer than those of NV drivers, most were within a commonly used 2.5-second guideline. CONCLUSIONS Most participants with HH had blind-side detection rates that seem incompatible with safe driving; however, the relationship of our simulator detection performance measures to on-road performance has yet to be established. In determining fitness to drive for people with HH, the results underscore the importance of individualized assessments including evaluations of blind-side hazard detection.

Driving with Hemianopia, II: Lane Position and Steering in a Driving Simulator

PURPOSE The hypothesis that drivers with homonymous hemianopia (HH) would take a lane position that increased the safety margin on their blind side was tested with a driving simulator. METHODS Twelve participants with HH (six right HH and six left; nine men; mean age, 50 years; range 31-72), and 12 matched current drivers with normal vision (NV) each completed approximately 120 minutes of simulator driving. Lane position and steering stability were evaluated for specific road segment types (straight segments, curves, and turns) in city and rural undivided highway driving. RESULTS The drivers with right HH held a lane position significantly (P = 0.001) to the left of NV drivers on the straight road segments and to a lesser extent on the curves. The drivers with left HH had a lane position similar to that of the NV drivers on straights and curves, but followed a significantly (P = 0.005) more rightward path on the left turns. CONCLUSIONS The results support the hypothesis that drivers with HH take a lane position that increases the safety margin on their blind side; however, absolute lane position varies as the steering maneuver and location of the risk from oncoming traffic change with road segment type.

Driving with hemianopia: IV. Head scanning and detection at intersections in a simulator.

PURPOSE Using a driving simulator, we examined the effects of homonymous hemianopia (HH) on head scanning behaviors at intersections and evaluated the role of inadequate head scanning in detection failures. METHODS Fourteen people with complete HH and without cognitive decline or visual neglect and 12 normally sighted (NV) current drivers participated. They drove in an urban environment following predetermined routes, which included multiple intersections. Head scanning behaviors were quantified at T-intersections (n = 32) with a stop or yield sign. Participants also performed a pedestrian detection task. The relationship between head scanning and detection was examined at 10 intersections. RESULTS For HH drivers, the first scan was more likely to be toward the blind than the seeing hemifield. They also made a greater proportion of head scans overall to the blind side than did the NV drivers to the corresponding side (P = 0.003). However, head scan magnitudes of HH drivers were smaller than those of the NV group (P < 0.001). Drivers with HH had impaired detection of blind-side pedestrians due either to not scanning in the direction of the pedestrian or to an insufficient scan magnitude (left HH detected only 46% and right HH 8% at the extreme left and right of the intersection, respectively). CONCLUSIONS Drivers with HH demonstrated compensatory head scan patterns, but not scan magnitudes. Inadequate scanning resulted in blind-side detection failures, which might place HH drivers at increased risk for collisions at intersections. Scanning training tailored to specific problem areas identified in this study might be beneficial.

Design for Simulator Performance Evaluations of Driving with Vision Impairments and Visual Aids

Driving simulator technology provides a safe method for evaluating the impact of vision loss on different components of the driving task and the potential efficacy of visual aids intended to compensate for a particular type of vision loss. Most previous investigations have used general driving scenarios. It is proposed here that scenarios with different task requirements be designed specifically to address the condition under investigation. As an example, the design of driving scenarios and tasks that are specific for the evaluation of one type of visual field loss, homonymous hemianopia, is described. Results of pilot studies show that even with a small sample size, the design is sufficiently sensitive to differentiate individuals with hemianopic visual field loss from control drivers. These results suggest that careful design of test situations, measurements, and analyses provides a strong basis for investigations of driving performance of individuals with specific types of vision impairment and could be used to evaluate the efficacy of low-vision driving aids.

Making virtual reality "more real" and the perception of potential collisions

Updated) Purpose: To see if making the experience in virtual reality closer to the “real world” experience (e.g. actually walking, rather than standing or sitting, in a walking simulator) affects task performance. Improved experience of “presence” might make performance in the virtual reality similar to real-world performance, whereas poor presence or an incorrect rendition might impair performance. Methods: We measured perception of a potential collision with stationary obstacles using four experimental situations to compare: standing or walking; walking with or without participant speed control; and correct or incorrect viewpoint. Participants stood or walked on a treadmill 75cm in front of a 95-degree-wide screen that displayed a “shopping mall” corridor with textured floor and shop fronts. Adult-man-size obstacles appeared for 1 second and participants indicated whether they would collide if they continued on the same path. Data for 14 participants were analyzed to find the participant’s perceived safe passing distance and decision quality. Results: When standing, participants had a slightly smaller perceived safe passing distance (p=0.07) and made better decisions (p=0.01) than when walking. Walking with and without participant speed control provided equivalent performance. The incorrect viewpoint biased the results to one side (p=0.08). Conclusions: Our attempts to increase realism did not alter perception of potential collisions. Our with-participant-speedcontrol walking condition required that the participant exert effort to propel the treadmill (i.e. not motorized), which might reduce task performance compared to a feedback-controlled motorized system. An incorrect viewpoint (rendition) caused a bias so obstacle side should be considered in data analysis. Other issues that might affect the experience of presence, including head-tracking and binocular view (stereo cue of flat screen), are under investigation. Supported in part by NIH grant EY12890