Quantifying the impact on navigation performance in visually impaired: Auditory information loss versus information gain enabled through electronic travel aids

Abstract

This study's purpose was to analyze and quantify the impact of auditory information loss versus information gain provided by electronic travel aids (ETAs) on navigation performance in people with low vision. Navigation performance of ten subjects (age: 54.9±11.2 years) with visual acuities >1.0 LogMAR was assessed via the Graz Mobility Test (GMT). Subjects passed through a maze in three different modalities: 'Normal' with visual and auditory information available, 'Auditory Information Loss' with artificially reduced hearing (leaving only visual information), and 'ETA' with a vibrating ETA based on ultrasonic waves, thereby facilitating visual, auditory, and tactile information. Main performance measures comprised passage time and number of contacts. Additionally, head tracking was used to relate head movements to motion direction. When comparing 'Auditory Information Loss' to 'Normal', subjects needed significantly more time (p<0.001), made more contacts (p<0.001), had higher relative viewing angles (p = 0.002), and a higher percentage of orientation losses (p = 0.011). The only significant difference when comparing 'ETA' to 'Normal' was a reduced number of contacts (p<0.001). Our study provides objective, quantifiable measures of the impact of reduced hearing on the navigation performance in low vision subjects. Significant effects of 'Auditory Information Loss' were found for all measures; for example, passage time increased by 17.4%. These findings show that low vision subjects rely on auditory information for navigation. In contrast, the impact of the ETA was not significant but further analysis of head movements revealed two different coping strategies: half of the subjects used the ETA to increase speed, whereas the other half aimed at avoiding contacts.

Fig 1. Graz mobility test.

The schematic shows the four different maze variants A, B, C, and D. Obstacles (small, medium, large, and the step) and the walls can be repositioned without effort between runs. Arrows show the entrance and exit of each variant, depending on the walking direction.

Fig 2. Endpoints.

The four measured endpoints (Passage time, Contacts, MARVA, and Orientation loss) in the three modalities (‘Normal’ with visual and auditory information available, ‘Auditory information loss’ with only visual information, and ‘ETA’ with tactile, visual, and auditory information) for each subject.

Fig 3. Angle distributions for the two groups EF (A) and ES (B).

The different behaviors of the two groups are reflected in the width of the distributions when comparing ‘Normal’ to ‘ETA’. Subjects who were faster with ‘ETA’ had narrower distributions which indicates that they spent more time in the lower angle range. The opposite effect can be observed in the ES group.