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Kristina Rand, Margaret Tarampi, Sarah Creem-Regehr, William Thompson; The importance of a visual horizon for distance judgments under severely degraded vision. Journal of Vision 2010;10(7):61. doi: 10.1167/10.7.61.
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Critical for understanding mobility in low vision is knowledge of one's ability to judge an object's location in the environment under low vision conditions. A recent study investigating distance judgments under severely degraded vision yielded surprising accuracy in a blind walking task (Tarampi et al., 2009). It is suggested in the current study that participants may have access to certain visual context cues despite the low vision manipulation. Specifically, the angle of declination from the visually defined horizon to the target on the ground may be used to determine distance.
To test this hypothesis, normally sighted individuals wore goggles that severely reduced acuity and contrast. All participants monocularly viewed targets which were placed on the ground in a large room at distances of 3, 4.5, or 6 meters. Targets were equated for visual angle, and viewed through a viewing box that restricted horizontal and vertical field of view in order to occlude the information provided by the sidewalls and ceiling. Participants were instructed to walk to the target location without vision. In one condition, the context in which participants viewed target objects was manipulated such that the perceived intersection of the floor and back wall appeared raised. If the visual frame of reference for the horizontal is used, this manipulation increases the angle of declination to the target, and should lead to an underestimation in distance compared to a condition where the floor is not changed. Preliminary results suggest individuals in the raised floor context condition are showing a decrease in distance estimates in a blind walking task relative to the control condition. These results support the account that reliance on the visually-defined horizon may have contributed, in part, to accuracy in previous blind walking performance under severely degraded vision. Subsequent manipulations will be performed to further explore this hypothesis.
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