Visual Search Training and Obstacle Avoidance in Adults with Visual Impairments

Abstract: This study assessed the effect of visual search training on the avoidance of obstacles by adults with visual impairments. A significant reduction in contacts with obstacles under mesopic conditions was found in individuals who received search training. This finding suggests that search training had a positive effect on mobility performance. ********** Mobility is the ability to move independently, safely, and efficiently through the environment. In the context of a visual impairment (that is, blindness or low vision), this movement is achieved primarily by walking. In a previous study, we found that visual search ability, assessed on a feature search task, was strongly associated with mobility performance in persons with severe visual impairments (Fuhr, Liu, & Kuyk, 2007). Specifically, reaction times on the feature search task were found to explain up to 67% of the variance in mobility performance in persons with visual impairments. We also found that although the participants with visual impairments searched more slowly than did the sighted participants, their reaction times were independent of the number of distracters, suggesting that the search was done in parallel (Kuyk, Liu, & Fuhr, 2005). Last, we found that, like the performance of sighted persons, the performance of persons with visual impairments on the search tasks improved with training (Liu, Kuyk, & Fuhr, 2007). Since the visual search performance of persons with visual impairments can be improved with training and is strongly associated with their mobility performance, an obvious question is: Will improved visual search result in improved mobility performance? The findings of several studies suggest that this may be the case. Dodds and Davis (1987) found that persons with visual impairments who received training in visual attention tasks that included detecting motion as a result of textural shearing, searching for a familiar shape embedded in an array of lines, and detecting a parafoveal target while monitoring a foveal one, improved not only their performance on the tasks, but their mobility performance. Virtual reality training of stroke patients with unilateral spatial neglect has also produced some encouraging results. After training in a virtual environment obstacle course, the patients looked more toward the neglected side (Katz et al., 2004), were less likely to bump into obstacles (Jaffe, 2004), made fewer errors in wheelchairs on a real obstacle course, and reported fewer falls and accidents during hospital stays (Jaffe, 2004; Webster, Szeto-Wong, McFarland, & Abadee, 2000). Some of the effects of training persisted after training had stopped. In such training, the virtual environment was comparable to a real environment in terms of visual content, and the patients were learning a set of visual skills in the virtual environment that was specifically related to mobility. The fact that the patients performed better in the real world after being trained in a virtual one suggested that their task-specific virtual experiences were partially transferable to real-world environments. In another study, 29 stroke patients with homonymous visual field defects without neglect were given 20 daily training sessions in visual search tasks (Pambakian, Mannan, Hodgson, & Kennard, 2004). The training resulted in a significant shortening of reaction times while searching and a small but significant improvement in activities of daily living (coin collecting, post box, bead threading, bead placing, and nut sorting), indicating that specific daily living skills may benefit from visual search training. Although the results of these studies are interesting, for different reasons they do not answer our question about the visual search training of persons with visual impairments. The improved mobility found by Dodds and Davis (1987) is more suggestive than definitive because changes across their three performance measures were not consistent. …