Influence of animation on dynamical judgments.

The motions of objects in the environment reflect underlying dynamical constraints and regularities. The conditions under which people are sensitive to natural dynamics are considered. In particular, the article considers what determines whether observers can distinguish canonical and anomalous dynamics when viewing ongoing events. The extent to which such perceptual appreciations are integrated with and influence common-sense reasoning about mechanical events is examined. It is concluded that animation evokes accurate dynamical intuitions when there is only 1 dimension of information that is of dynamical relevance. This advantage is lost when the observed motion reflects higher dimension dynamics or when the kinematic information is removed or degraded.     

Observers’ sensitivity to dynamic anomalies in collisions

The present study examined observers’ ability to discriminate canonical and dynamically anomalous collisions that were presented in either frictionless or frictional systems. Whereas previous research has provided qualitative demonstrations that dynamic information can be extracted from visual events, the current study provides a parametric assessment of observers’ sensitivity to dynamic invariants. Our findings indicate that observers are competent when viewing both familiar, terrestrial (frictional) systems and unfamiliar but computationally simpler, 0-G (frictionless) systems. Thus, our sensitivity to these dynamic invariants in visual events is robust in natural systems whose dynamic properties differ from those of the environment in which we evolved and developed.     

Infant sensitivity to figural coherence in biomechanical motions

Two experiments assessed infant sensitivity to figural coherence in point-light displays moving as if attached to the major joints of a walking person. Experiment 1 tested whether 3- and 5-month-old infants could discriminate between upright and inverted versions of the walker in both moving and static displays. Using an infant-control habituation paradigm, it was found that both ages discriminated the moving but not the static displays. Experiment 2 was designed to clarify whether or not structural invariants were extracted from these displays. The results revealed that (1) moving point-light displays with equivalent motions but different topographic relations were discriminated while (2) static versions were not, and (3) arrays that varied in the amount of motion present in different portions of the display were also not discriminated. These results are interpreted as indicating that young infants are sensitive to figural coherence in displays of biomechanical motion.     

THE PRICE OF EXPERTISE:

Abstract— When shown a idled container, people often fail to appreciate that the surface of the liquid contained within should remain horizontal with respect to the ground. This study investigated how amenable this bias is to experience in relevant everyday situations. Surprisingly, liquid surfaces that waitresses and bartenders considered natural deviated even more from horizontal than was the case for comparison groups. This finding is, to our knowledge, the only documented case in which performance declines with experience. We suggest that practical experience promotes a functionally relative perspective, in which the orientation of the liquid's surface is evaluated relative to that of its container as opposed to being related directly to the surrounding environment. The container-relative perspective, in turn, evokes a perceptual bias that is responsible for the systematic errors observed on this task.     

Perceiving geographical slant

People judged the inclination of hills viewed either out-of-doors or in a computer-simulated virtual environment. Angle judgments were obtained by having people (1) provide verbal estimates, (2) adjust a representation of the hill’s cross-section, and (3) adjust a tilt board with their unseen hand. Geographical slant was greatly overestimated according to the first two measures, but not the third. Apparent slant judgments conformed to ratio scales, thereby enhancing sensitivity to the small inclines that must actually be traversed in everyday experience. It is proposed that the perceived exaggeration of geographical slant preserves the relationship between distal inclination and people’s behavioral potential. Hills are harder to traverse as people become tired; hence, apparent slant increased with fatigue. Visually guided actions must be accommodated to the actual distal properties of the environment; consequently, the tilt board adjustments did not reflect apparent slant overestimations, nor were they influenced by fatigue. Consistent with the fact that steep hills are more difficult to descend than to ascend, these hills appeared steeper when viewed from the top.     

Rotational and translational components of motion parallax: observers' sensitivity and implications for three-dimensional computer graphics

The motion of objects during motion parallax can be decomposed into 2 observer-relative components: translation and rotation. The depth ratio of objects in the visual field is specified by the inverse ratio of their angular displacement (from translation) or equivalently by the inverse ratio of their rotations. Despite the equal mathematical status of these 2 information sources, it was predicted that observers would be far more sensitive to the translational than rotational component. Such a differential sensitivity is implicitly assumed by the computer graphics technique billboarding, in which 3-dimensional (3-D) objects are drawn as planar forms (i.e., billboards) maintained normal to the line of sight. In 3 experiments, observers were found to be consistently less sensitive to rotational anomalies. The implications of these findings for kinetic depth effect displays and billboarding techniques are discussed.     

Eye height scaling of absolute size in immersive and nonimmersive displays

Eye-height (EH) scaling of absolute height was investigated in three experiments. In Experiment 1, standing observers viewed cubes in an immersive virtual environment. Observers' center of projection was placed at actual EH and at 0.7 times actual EH. Observers' size judgments revealed that the EH manipulation was 76.8% effective. In Experiment 2, seated observers viewed the same cubes on an interactive desktop display; however, no effect of EH was found in response to the simulated EH manipulation. Experiment 3 tested standing observers in the immersive environment with the field of view reduced to match that of the desktop. Comparable to Experiment 1, the effect of EH was 77%. These results suggest that EH scaling is not generally used when people view an interactive desktop display because the altitude of the center of projection is indeterminate. EH scaling is spontaneously evoked, however, in immersive environments.     

Perception-action dissociations of a walkable Müller-Lyer configuration

These studies examined the role of spatial encoding in inducing perception-action dissociations in visual illusions. Participants were shown a large-scale Müller-Lyer configuration with hoops as its tails. In Experiment 1, participants either made verbal estimates of the extent of the Müller-Lyer shaft (verbal task) or walked the extent without vision, in an offset path (blind-walking task). For both tasks, participants stood a small distance away from the configuration, to elicit object-relative encoding of the shaft with respect to its hoops. A similar illusion bias was found in the verbal and motoric tasks. In Experiment 2, participants stood at one endpoint of the shaft in order to elicit egocentric encoding of extent. Verbal judgments continued to exhibit the illusion bias, whereas blind-walking judgments did not. These findings underscore the importance of egocentric encoding in motor tasks for producing perception-action dissociations.     

Perceiving distance: a role of effort and intent

Perceiving egocentric distance is not only a function of the optical variables to which it relates, but also a function of people's current physiological potential to perform intended actions. In a set of experiments, we showed that, as the effort associated with walking increases, perceived distance increases if the perceiver intends to walk the extent, but not if the perceiver intends to throw. Conversely, as the effort associated with throwing increases, perceived distance increases if people intend to throw to the target, but not if they intend to walk. Perceiving distance combines the geometry of the world with our behavior goals and the potential of our body to achieve these goals.