Indoor Spatial Updating With Impaired Vision

Abstract

Purpose: Spatial updating is the ability to keep track of position and orientation while moving through an environment. We asked how normally sighted and visually impaired subjects compare in spatial updating and in estimating room dimensions.

Methods: Groups of 32 normally sighted, 16 low-vision, and 16 blind subjects estimated the dimensions of six rectangular rooms. Updating was assessed by guiding the subjects along three-segment paths in the rooms. At the end of each path, they estimated the distance and direction to the starting location, and to a designated target. Spatial updating was tested in five conditions ranging from free viewing to full auditory and visual deprivation.

Results: The normally sighted and low-vision groups did not differ in their accuracy for judging room dimensions. Correlations between estimated size and physical size were high. Accuracy of low-vision performance was not correlated with acuity, contrast sensitivity, or field status. Accuracy was lower for the blind subjects. The three groups were very similar in spatial-updating performance, and exhibited only weak dependence on the nature of the viewing conditions.

Conclusions: People with a wide range of low-vision conditions are able to judge room dimensions as accurately as people with normal vision. Blind subjects have difficulty in judging the dimensions of quiet rooms, but some information is available from echolocation. Vision status has little impact on performance in simple spatial updating; proprioceptive and vestibular cues are sufficient.

Figure 1

Photos from the seven rooms. The dimensions of the rooms were (Door Side × Non-Door Side in feet) (A) 7.6 × 15.2, (B) 16.2 × 20.0, (C) 19.9 × 22.1, (D) 32.7 × 16.6, (E) 33.2 × 16.6, (F) 27.1 × 23.7, (G) 17.4 × 19.0.

Figure 2

Schematic diagram illustrating the three-segment path. An experimenter guided the subject along a three-segment path beginning at the doorway (starting location). At the first waypoint, the subject dropped a beanbag (target). At the end of the path, the subject made judgments about the distance and direction to the starting location and the target. (Adapted from Fig. 2 in Legge et al.)

Figure 3

Estimates of room-size length (Door Side) for 16 low-vision subjects. Each panel of the figure shows the subject's estimate of the Door Side length as a function of the physical length. The panels are arranged in order of increasing logMAR acuity from top left (logMAR 0.1) to lower right (logMAR 1.96). The single letters in each panel represent field loss categorized as central (C), peripheral (P), or none (N). Red lines are linear regression fits (with parameters in Table 3), and black diagonal lines represent perfect performance.

Figure 4

Estimates of room-size length (Door Side) for 16 blind subjects. Each panel in the figure shows the subject's estimate of the Door Side length as a function of the physical length. Red lines are linear regression fits (with parameters in Table 4), and black diagonal lines represent perfect performance.

Figure 5

Errors in estimating distance and direction to the starting location and the target for three groups (normally sighted, low vision, and blind) for five viewing conditions. The bars represent group mean absolute errors (with 95% confidence intervals) in feet for the starting distance (upper left), for the target distance (upper right), and in degrees for the starting direction (lower left) and target direction (lower right).