Academic journal article Perception and Psychophysics

Progressive Locomotor Recalibration during Blind Walking

Academic journal article Perception and Psychophysics

Progressive Locomotor Recalibration during Blind Walking

Article excerpt

Blind walking has become a common measure of perceived target location. This article addresses the possibility that blind walking might vary systematically within an experimental session as participants accrue exposure to nonvisual locomotion. Such variations could complicate the interpretation of blind walking as a measure of perceived location. We measured walked distance, velocity, and pace length in indoor and outdoor environments (1.5-16.0 m target distances). Walked distance increased over 37 trials by approximately 9.33% of the target distance; velocity (and to a lesser extent, pace length) also increased, primarily in the first few trials. In addition, participants exhibited more unintentional forward drift in a blindfolded marching-in-place task after exposure to nonvisual walking. The results suggest that participants not only gain confidence as blind-walking exposure increases, but also adapt to nonvisual walking in a way that biases responses toward progressively longer walked distances.

Over the last quarter century, walking has been increasingly used as a means of measuring perceived object locations (e.g., Allen, Kirasic, Rashotte, & Haun, 2004; Creem-Regehr, Willemsen, Gooch, & Thompson, 2005; Loomis, Da Silva, Philbeck, & Fukusima, 1996; Philbeck, Loomis, & Beall, 1997; Rieser, Ashmead, Talor, & Youngquist, 1990; Thomson, 1980; Wu, Ooi, & He, 2004, among a host of others). As this method is typically used, participants view a target under well-lit viewing conditions, then cover their eyes and attempt to walk without assistance to the remembered target location. This method is known as visually directed walking, open-loop walking, and blind (or blindfolded) walking. Under well-lit viewing conditions, accuracy is generally high for target distances up to at least 22 m, although there is some undershooting for larger distances (Andre & Rogers, 2006). This good accuracy has been taken as evidence that observers accurately perceive the target location as seen from their initial viewpoint (Loomis et al., 1996; Philbeck & Loomis, 1997). This interpretation relies upon the assumption that the walking is well calibrated, so that the distance observers walk accurately reflects their perceived target distance.

Recent work has shown that exposure to nonvisual locomotion can itself affect the calibration of nonvisual locomotion (Durgin et al., 2005; Rieser, Pick, Ashmead, & Garing, 1995). The impact of this on blind walking as a measure of perceived distance is currently unknown. This is an important issue for at least two reasons. First, in many blind-walking studies, participants are provided with several minutes of exposure to nonvisual walking prior to testing, often on the assumption that this will increase the participants' feelings of confidence and safety while walking blindfolded (Bigel & Ellard, 2005; Creem- Regehr et al., 2005; Elliott, 1987; Mohler et al., 2007; Philbeck & Loomis, 1997; Rieser et al., 1995; Steenhuis & Goodale, 1988). Increased confidence may improve response precision and reduce any tendency to stop walking sooner than intended, due to hesitancy. Another effect of the exposure to nonvisual walking, however, may be to alter participants' locomotor calibration prior to testing, meaning that the walked distance may not accurately reflect the perceived target location during the experiment proper. Second, in blind-walking experiments, participants accumulate exposure to nonvisual locomotion while generating their responses. If exposure to nonvisual walking alters the calibration of the walking responses themselves (e.g., by creating a general tendency to walk farther and farther for each target as the experiment unfolds), it is possible that the impressive accuracy typically observed in blind-walking studies is, to some degree, an artifact of recalibration that takes place during the experiment.

Our definition of calibration in the context of blind walking is quite broad: It is the degree of correspondence between the physical target location and the distance walked when one attempts to walk to the target location. …

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