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...
The motor theory of biological motion perception hypothesizes that motor commands (or records thereof) are used to recognize human event recognition, motor theory, biological motion perception movements when they are visually perceived. However, current theories of human action render this motor theory redundant. This chapter argues that motor commands are not responsible for the specific forms of different kinds of movements such as running or walking. Rather, passive dynamical organizations are used to generate forms of movement that are then controlled by parametrically adjusting the dynamics. However, it is the dynamically generated movement forms that can provide the information that allows biological motions to be perceived and recognized for what they are. This possibility has been systematically investigated in a number of studies inspired by an ecological approach to visual event perception. The approach hypothesizes that lawfully generated information must be available to allow perception and support recognition. Trajectory forms generated by event dynamics would provide such information. The studies have shown that trajectory forms can be used by human observers to recognize events.
Previous studies have shown that people can use the information in trajectory forms to recognize visual events. A trajectory form is composed of the path of motion and the change in speed along that path. In past studies, however, only sensitivity to trajectory forms viewed from a single perspective was examined. The optical components change when an event is viewed from different perspectives, and the projected form of the trajectory is transformed. Does event recognition exhibit constancy despite these changes? In Experiment 1, participants were familiarized with five different trajectory forms viewed from a single perspective. Then the participants had to identify the same events viewed from different perspectives: from the side, at an angle, and entirely in depth. The participants exhibited perceptual constancy. Experiment 2 revealed, however, that both the change in optical components and the perspective transformations affected recognition.
Older adults and college students were tested with two procedures that measure stereotypy and response variability. In Experiment 1 subjects guided a marker through a 6 by 6 matrix by pressing two computer keys. Points were awarded on either a continuous or variable ratio 3 schedule of reinforcement. Points were exchanged for money. Continuous reinforcement produced significantly higher stereotypy than intermittent reinforcement did in both age groups. A difference was found in stereotypy between age groups during the variable ratio schedule. This difference may have been caused by the greater task anxiety of the older adults. In Experiment 2 subjects were tested using the matrix procedure with the consequence that response variability was differentially reinforced. Four levels of variability were tested in the two age groups. Both older and younger subjects learned to vary response patterns to obtain points. The results are discussed in the context of cautiousness as an age-related explanation for behavior.
The authors investigated whether infants are sensitive to visual event trajectory forms, and whether they are sensitive to the underlying dynamics of trajectory forms. The authors habituated 8-month-old infants to a videotaped event run either forward or reversed in time and then switched them to the same event run in the opposite direction. Infants dishabituated when switched to the event with the novel direction in time, indicating sensitivity to the form of the trajectory. Infants exhibited equivalent habituation rates and looking times for forward and reversed events, thus failing to provide evidence that infants are sensitive to the underlying dynamics. In a partial replication of this first experiment, the same pattern of results was found. Both experiments revealed infant sensitivity to the trajectory forms, but not the underlying dynamics of events. The authors discuss implications for methods used in infant event perception studies.
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