No abstract

The visual accessibility of a space refers to the effectiveness with which vision can be used to travel safely through the space. For people with low vision, the detection of steps and ramps is an important component of visual accessibility. We used ramps and steps as visual targets to examine the interacting effects of lighting, object geometry, contrast, viewing distance and spatial resolution. Wooden staging was used to construct a sidewalk with transitions to ramps or steps. 48 normally sighted subjects viewed the sidewalk monocularly through acuity-reducing goggles, and made recognition judgments about the presence of the ramps or steps. The effects of variation in lighting were milder than expected. Performance declined for the largest viewing distance, but exhibited a surprising reversal for nearer viewing. Of relevance to pedestrian safety, the step up was more visible than the step down. We developed a probabilistic cue model to explain the pattern of target confusions. Cues determined by discontinuities in the edge contours of the sidewalk at the transition to the targets were vulnerable to changes in viewing conditions. Cues associated with the height in the picture plane of the targets were more robust.

These analyses showed that (1) an exponential-decay function fits MNREAD data very well, (2) NLME modeling provides a statistical framework for analyzing MNREAD data, and (3) NLME analysis provides a way of estimating MNREAD parameters even for incomplete data sets. The present results demonstrate the potential value of NLME modeling for clinical vision data.

Walking without vision results in veering, an inability to maintain a straight path that has important consequences for blind pedestrians. We addressed whether the source of veering in the absence of visual and auditory feedback is better attributed to errors in perceptual encoding or undetected motor error. Three experiments had the following results: no significant differences in the shapes of veering trajectories were found between blind and blindfolded participants; accuracy in detecting curved walking paths was not correlated with simple measures of veering behavior; and explicit perceptual cues to initial walking direction did not reduce veering. We present a model that accounts for the major characteristics of our participants' veering behavior by postulating three independent sources of undetected motor error: initial orientation, consistent biases in step direction, and most importantly variable error in individual steps. KeywordsVeering; Walking; Locomotion; Motor Noise; Blind MobilityIn the context of human locomotion, veering is any deviation from an intended path. When walking an intended straight line, veering is the lateral deviation from that line. Veering by human pedestrians becomes evident when visual targeting cues are absent as in cases of blindness or severely reduced visibility (e.g., walking in the dark or in a blizzard). For blind people, veering can be an everyday problem, potentially threatening safety when crossing a street at a busy intersection. Non-visual environmental cues such as wind direction, slope of the ground plane, or directional acoustic cues, can help blind pedestrians accurately navigate across spaces. Unfortunately, reliable non-visual cues are not always available. In the absence of such cues, our research and the findings of others (to be reviewed below) show that blind people veer away from intended straight pathways. The purpose of the present study was to answer the question: What causes this veering behavior? Our research suggests that a simple Corresponding Author: Christopher S. Kallie, University of Minnesota, Department of Psychology, N218 Elliott Hall, 75 East River Road, Minneapolis, MN 55455. email: kallie@umn.edu. Publisher's Disclaimer: The following manuscript is the final accepted manuscript. It has not been subjected to the final copyediting, fact-checking, and proofreading required for formal publication. It is not the definitive, publisher-authenticated version. The American Psychological Association and its Council of Editors disclaim any responsibility or liabilities for errors or omissions of this manuscript version, any version derived from this manuscript by NIH, or other third parties. The published version is available at http://www.apa.org/journals/xhp NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript explanation -unperceived motor noise at the level of individual steps -may explain the veering behavior of both blind pedestrians and sighted pedestrians who are blindfolded.Some early proposal...