Reaching measures of monocular distance perception: Forward versus side-to-side head movements and haptic feedback

Abstract

Weinvestigated whether forward or side-to-side head movements yielded more accurate and precise monocular egocentric distance information, as shown by performance in a reaching task. Observers wore a head-mounted camera and display to isolate the optic flow generated by their head movements and had to reach to align a stylus directly under a target surface. Performance in the two head movement conditions was also tested with normal monocular vision. Wetested performance in the two head movement conditions when the observers were given haptic feedback and compared performance when haptic feedback was removed. Performance was both more accurate and more precise in the forward head movement condition than in the side-to-side head movement condition. Performance in the side-to-side condition also deteriorated more after the removal of haptic feedback than did performance in the forward head movement condition. In the normal monocular condition, performance was comparable for the two head movement conditions. The implications for enucleated patients are discussed.A problem in perceiving definite distances is that spatial metrics are lost in the projection from surfaces into optical patterns (Bingham, 1993b;Bingham & Pagano, 1998)1. So, how do people obtain information about definite distances? This problem is especially salient for enucleated patients (people who have had one eye removed and are thus permanently monocular), because they cannot use binocular vision to obtain distance information. Despite this, monocular people do not appear to have large problems performing everyday tasks that require perceiving the distance of objects. We do not normally see people walk into walls or misguide their reach when they aim to grab a coffee mug. So, definite distance must somehow be perceived. One possible source of information arises from the patterns of optic flow produced by voluntary self-movement, which is necessarily accompanied by somatosensory information about head movement. Such information about the distance or velocity of head movements could be used to scale optic flow information about distance (Bingham & Stassen, 1994; S. Rogers & B. 1. Rogers, 1992).The possibility of using head movements to scale distance is especially important for monocular observers. Servos, Goodale, and Jakobson (1992) compared the abilities ofmonocular and binocular observers to use vision to guide reaching. They found that in normal lighting, monocular observers underestimated distance, relative to binocThis research was supported by the National Institute of Health, NEI Grant I ROI EY1l741-0IA. We thank Michael Muchisky for assistance in data collection, as well as G. John Andersen and two anonymous reviewers for their helpful comments and suggestions on an earlier draft of this manuscript. Correspondence concerning this article should be addressed to E. A. Wickelgren, Department of Psychology, Indiana University, Bloomington, IN 47405 (e-mail: ewickelg@indiana.edu). ular observers. The monocular reaches took longer and had lower pe...

Integration of disparity and velocity information for haptic and perceptual judgments of object depth

“…This result replicates the finding that haptic feedback resulting from contact with actual targets produces calibration and it allows reaches to become more precise Wickelgren, McConnell, & Bingham, 2000; see also Bingham, Zaal, Robin, & Shull, 2000;, even though it does not necessarily correct shape distortions (Bingham et al, 2001). Interestingly, we found an increase in precision even if haptic feedback was provided only to a predictable subset of prehension movements directed to a different spatial target.…”

Contribution of extraretinal signals to the scaling of object distance during self-motion

“…Further studies on reaching under monocular viewing conditions by Bingham and Stassen (1994) confirmed the finding that head movements in the direction of the target facilitate the recovery of its absolute distance (Pagano & Bingham, 1998). However, these results are specific for reaching space and, in some cases, refer to experimental conditions in which other types of sensory information were available, such as haptic feedback (Wickelgren, McConnell, & Bingham, 2000). Our study extends the investigation well beyond reaching space and was conducted with standing subjects performing head movements of larger amplitudes in unrestrained conditions.…”

Calibrating reach distance to visual targets.

“…The apparent conflict can be reconciled by the fact that reports of inaccurate distance perception have come from situations in which participants received no feedback about the outcome of their movement (i.e., they remained in a visual-open-loop environment throughout the experiment). In line with this, a number of research studies have demonstrated that reaches increasingly drift from visually targeted locations as feedback information is removed (Bingham, Zaal, Robin, & Shull, 2000;Vindras & Viviani, 1998;Wann & Ibrahim, 1992;Wickelgren, McConnell, & Bingham, 2000). These observations paint a picture of a nervous system that continually needs to adapt its behavior because it is subject to biological noise.…”