Indoor Spatial Updating with Reduced Visual Information

Abstract

Purpose: Spatial updating refers to the ability to keep track of position and orientation while moving through an environment. People with impaired vision may be less accurate in spatial updating with adverse consequences for indoor navigation. In this study, we asked how artificial restrictions on visual acuity and field size affect spatial updating, and also judgments of the size of rooms.

Methods: Normally sighted young adults were tested with artificial restriction of acuity in Mild Blur (Snellen 20/135) and Severe Blur (Snellen 20/900) conditions, and a Narrow Field (8°) condition. The subjects estimated the dimensions of seven rectangular rooms with and without these visual restrictions. They were also guided along three-segment paths in the rooms. At the end of each path, they were asked to estimate the distance and direction to the starting location. In Experiment 1, the subjects walked along the path. In Experiment 2, they were pushed in a wheelchair to determine if reduced proprioceptive input would result in poorer spatial updating.

Results: With unrestricted vision, mean Weber fractions for room-size estimates were near 20%. Severe Blur but not Mild Blur yielded larger errors in room-size judgments. The Narrow Field was associated with increased error, but less than with Severe Blur. There was no effect of visual restriction on estimates of distance back to the starting location, and only Severe Blur yielded larger errors in the direction estimates. Contrary to expectation, the wheelchair subjects did not exhibit poorer updating performance than the walking subjects, nor did they show greater dependence on visual condition.

Discussion: If our results generalize to people with low vision, severe deficits in acuity or field will adversely affect the ability to judge the size of indoor spaces, but updating of position and orientation may be less affected by visual impairment.

Fig 1. Photos from the seven rectangular test spaces.

The dimensions of the seven spaces were (Door side × Non-door side in ft) A: 7.6 × 15.2. B: 4.3 × 44.4. C: 16.2 × 20.0. D: 19.9 × 22.1. E: 32.7 × 16.6. F: 33.2 × 16.6. G: 27.1 × 23.7.

Fig 2. Schematic diagram illustrating the three-segment path.

An experimenter guided the subject along a three-segment path beginning at the doorway. At the first waypoint, the subject dropped a beanbag, referred to as the target. At the end of the path, the subject made judgments about the distance and direction to the starting location and target, and also estimated the door side and non-door side dimensions of the space.

Fig 3. Experiment 1: Walking. Estimates of Room Dimensions.

Mean values and 95% confidence intervals for the absolute error in the Control condition are plotted as a function of physical length for the Door Side (panel A) and Non-Door Side (Panel B). Straight lines show the LME fit. Panels C and D show the additive errors associated with the five viewing conditions, estimated from the LME model.

Fig 4. Experiment 1: Walking. Spatial Updating.

Panels A and B show the mean absolute errors for estimates of the distance and direction to the Start Location (room door). Panels C and D show the mean absolute errors for estimates of the distance and direction to the Target Location (beanbag). Error bars represent 95% confidence intervals.

Fig 5. Experiment 2: Wheelchair. Estimates of Room Dimensions.

Mean values and 95% confidence intervals for the absolute error in the Control condition are plotted as a function of physical length for the Door Side (panel A) and Non-Door Side (Panel B). Straight lines show the LME fit. Panels C and D show the additive errors associated with the three viewing conditions, estimated from the LME model.

Fig 6. Experiment 2: Wheelchair. Spatial Updating.

Panels A and B show the mean absolute errors for estimates of the distance and direction to the Start Location (room door). The orange bars are data for wheelchair subjects, and the blue bars are data for walking subjects replotted from Experiment 1. Error bars represent 95% confidence intervals.