Mary K. Kaiser

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.

Visual acceleration detection: Effect of sign and motion orientation

Thresholds for the detection of constant acceleration and deceleration of a discrete object moving along horizontal and vertical axes were studied. A staircase methodology was used to determine thresholds for three average velocities (0.7, 1.2, and 1.7 deg/sec). Thresholds, expressed as the proportion of velocity change, did not differ significantly among the average velocities; thus, a consistent Weber-like fraction is suggested by the data. Furthermore, there was an interaction between the axis of motion (horizontal or vertical) and the sign of the velocity change (acceleration or deceleration): accelerations were easier to detect along the vertical axis, decelerations along the horizontal axis.

The development of beliefs about falling objects

Previous studies have shown that many adults have striking misconceptions about the motions of objects in seemingly simple situations. The present two studies explored the development of knowledge about motion by examining children’s predictions about the movement of an object in two types of situations. In one type of situation, children predicted where a ball would land if it rolled off the edge of a table and fell to the floor. In the other type of situation, children judged where the same ball would land if it were dropped from a moving model train and fell the same distance to the floor. Younger children (preschool and kindergarten) generally thought that the ball would fall straight down in both situations. At older ages, children were more aware that the ball rolling from the table would continue to move forward while falling. For the ball dropped from the train, however, the older children were no more aware of the ball’s forward motion than were younger children. The results are interpreted in terms of general cognitive capabilities and perceptual experiences that contribute to the development of knowledge about the world.

Understanding wheel dynamics.

In five experiments, assessments were made of peoples understandings about the dynamics of wheels. It was found that undergraduates make highly erroneous dynamical judgments about the motions of this commonplace event, both in explicit problem-solving contexts and when viewing ongoing events. These problems were also presented to bicycle racers and high-school physics teachers; both groups were found to exhibit misunderstandings similar to those of naive undergraduates. Findings were related to our account of dynamical event complexity. The essence of this account is that people encounter difficulties when evaluating the dynamics of any mechanical system that has more than one dynamically relevant object parameter. A rotating wheel is multidimensional in this respect: in addition to the motion of its center of mass, its mass distribution is also of dynamical relevance. People do not spontaneously form the essential multidimensional quantities required to adequately evaluate wheel dynamics.

Perceptual Bias for Forward-Facing Motion

When an occluded horizontal row of shapes is shifted laterally, apparent motion can he experienced in either the leftward or the rightward direction. Four experiments provide evidence for a motion bias in the direction that shapes appear to face. The bias tended to be largest when directionality was specified geometrically (e.g., triangles), next largest when it was specified biologically (e.g., mice), and absent when it was specified calligraphically (e.g., letter R). The bias increased parametrically as a function of triangle pointedness and was consistent with the directional interpretation of an ambiguous duck-rabbit. The results support the existence of a cognitively specified forward-facing attribute that can influence experienced direction of motion.

The development of sensitivity to causally relevant dynamic information

The present study examined whether younger observers (kindergartners, second graders, and fourth graders) could extract relative weight information from collisions and also lifting events, and if they could judge whether collisions were natural (i.e., momentum conserving) or anomalous (non-momentum conserving). 20 children at each age and 20 adults viewed videotapes of 8 collisions (4 natural, 4 anomalous) and 6 sequences of lifting events. Observers also viewed sequences of static images taken from these events. Observers at all grade levels were able to reliably judge relative weight in both collisions and lifting events, and could differentiate between natural and anomalous collisions. Performance was much poorer when static sequences of the events were viewed, especially for the young children. A consistent age trend was noted across tasks: adults performed better than second and fourth graders who, in turn, performed better than kindergartners. In addition, there was evidence that younger children were differentially aided when the kinematics of the event made the kinetics more pronounced.

Perceived orientation in physical and virtual environments: changes in perceived orientation as a function of idiothetic information available

Two experiments examined perceived spatial orientation in a small environment as a function of experiencing that environment under three conditions: real-world, desktop-display (DD), and head-mounted display (HMD). Across the three conditions, participants acquired two targets located on a perimeter surrounding them, and attempted to remember the relative locations of the targets. Subsequently, participants were tested on how accurately and consistently they could point in the remembered direction of a previously seen target. Results showed that participants were significantly more consistent in the real-world and HMD conditions than in the DD condition. Further, it is shown that the advantages observed in the HMD and real-world conditions were not simply due to nonspatial response strategies. These results suggest that the additional idiothetic information afforded in the realworld and HMD conditions is useful for orientation purposes in our presented task domain. Our results are relevant to interface design issues concerning tasks that require spatial search, navigation, and visualization.

Information Integration in Judgements of Time to Contact

Time to contact (TTC) is specified optically by tau, and studies suggest that observers are sensitive to this information. However, TTC judgements also are influenced by other sources of information, including pictorial depth cues. Therefore, it is useful to identify these sources of information and to determine whether and how their effects combine when multiple sources are available. We evaluated the effect of five depth cues on TTC judgements. Results indicate that relative size, height in field, occlusion, and motion parallax influence TTC judgements. When multiple cues are available, an integration (rather than selection) strategy is used. Finally, the combined effects of multiple cues are not always consistent with a strict additive model and may be task dependent.

TIME-TO-PASSAGE JUDGMENTS IN NONCONSTANT OPTICAL FLOW FIELDS

The time until an approaching object will pass an observer (time to passage, or TTP) is optically specified by a global flow field even in the absence of local expansion or size cues. Kaiser and Mowafy (1993) have demonstrated that observers are in fact sensitive to this global flow information. The present studies investigate two factors that are usually ignored in work related to TTP: (1) non-constant motion functions and (2) concomitant eye rotation. Non-constant velocities violate an assumption of some TTP derivations, and eye rotations may complicate heading extraction. Such factors have practical significance, for example, in the case of a pilot accelerating an aircraft or executing a roll. In our studies, a flow field of constant-sized stars was presented monocularly on a large screen. TTP judgments had to be made on the basis of one target star. The flow field varied in its acceleration pattern and its roll component. Observers did not appear to utilize acceleration information. In particular, TTPs with decelerating motion were consistently underestimated. TTP judgments were fairly robust with respect to roll, even when roll axis and track vector were decoupled. However, substantial decoupling between heading and track vector led to a decrement in performance, in both the presence and the absence of roll.

Things that go bump in the light: on the optical specification of contact severity

Psychologists are intrigued with the idea that optical variables can specify not only the time until an object impacts an observer but also the severity of the impact. However, the mapping between the optical variables (tau and .tau) and the kinematic variables (velocity, acceleration) has been misstated, erroneously implying that there exist critical values of the optical variables used for locomotion and control. In this commentary, the mathematical relationship between the optical and kinematic variables is reexamined and the erroneous assumptions that have led to the proposal of critical values are show. Also examined are the empirical data on deceleration to approach (particularly from active control paradigms) to assess whether the proposed optical variables are likely candidates for control strategies. Finally, problems associated with numerical approximations to dynamic systems, particularly when analytic solutions exist, are discussed.