Vehicle handling skills of drivers with hemianopia: a simulator assessment

Although prior studies suggested that hemianopia may have adverse effects on vehicle handling, little attention has been paid to how these effects might vary with the type of road segment and the side of the vision loss. We conducted a simulator-based study to systematically investigate the effect of hemianopia on vehicle-handling (steering and lateral-lane position) for specific road segments (straights, curves and turns). In this paper we report results for individual drivers to illustrate our ability to develop measures of vehicle-control skills that probe performance of drivers with hemianopia and normal vision for specific road segments. Analyzing any driving measure across the whole drive is likely to hide important information and may result in false interpretation. Our examples illustrate that lateral lane offset varied with road segment type, and that drivers with right-sided and left-sided field loss exhibited different lane position biases, which also varied with segment type. Hemianopia may adversely affect a driver's ability to control the steering of a vehicle, and hence may impact lane positioning skills. When driving in a simulator, drivers with hemianopia were reported to make more lane boundary crossings and had greater variability in lane position than normally-sighted drivers. 4 However, in that study, only 5 minutes of driving was evaluated and performance was scored across the entire drive without differentiating the various types of roadway geometries (straights, curves, or turns). Furthermore, the small sample (n = 6) included drivers with hemianopia and quadrantanopia, with and without hemi-spatial neglect, making it difficult to isolate the effects of the visual field loss from the effects of hemi-spatial neglect. In a recent on-road study, driving examiners frequently commented on the unstable steering of hemianopic drivers, but quantitative measures of steering stability were not reported. 5 In another recent on-road study, drivers with hemianopia who were rated unsafe to drive had problems with lane positioning and steadiness of steering (scored on 3-point scales by raters in the back seat). 6 Although these studies provide evidence that hemianopia has adverse effects on steering and lane positioning skills, none addressed whether the effects varied with the type of roadway segment. Drivers with hemianopia might have greater difficulty on specific types of road geometries and these effects may be masked when studied across an entire drive. Therefore, in this study, we evaluated steering and lateral lane position of drivers with hemianopia and case-matched normally-sighted control drivers for specific road segments (straights, curves and turns). In addition, we examined whether there were any lateralized differences in lane position between participants with right and left hemianopia. As some aspects of the data analyses are still being developed, here we report only results for individual drivers to illustrate how the analyses address our research questions.