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.

Recent developments in computer engineering have greatly enhanced the capabilities of display technology. As displays are no longer limited to simple alphanumeric output, they can present a wide variety of graphic information, using either static or dynamic presentation modes. At the same time that interface designers exploit the increased capabilities of these displays, they must be aware of the inherent limitation of these displays. Generally, these limitations can be divided into those that reflect limitations of the medium (e.g., reducing three-dimensional representations onto a two-dimensional projection) and those reflecting the perceptual and conceptual biases of the operator. This paper considers the advantages and limitations of static and dynamic graphic displays. Rather than enter into the discussion of whether dynamic or static displays are superior, we explore general advantages and limitations which are contextually specific to each type of display.

The advantages and limitations of using computer-animated stimuli in studying motion perception are discussed. Most current programs of motion perception research could not be pursued without the use of computer graphics animation. Computer-generated displays afford latitudes of freedom and control that are almost impossible to attain through conventional methods. There are, however, limitations to this presentational medium. At present, computer-generated displays present simplified approximations of the dynamics in natural events. We know very little about how the differences between natural events and computer simulations influence perceptual processing. In practice, we tend to assume that the differences are irrelevant to the questions under study and that findings with computer-generated stimuli will generalize to natural events.

The advantages and imitations of using computer-animated stimuli in studying motion perception are presented and discussed. perception research could not be pursued without the use of computer graphics animation. Computer-generated displays afford latitudes of freedom and control that are almost impossible to attain through conventional methods. There are, however, limitations to this presentational medium. At present, computer-generated displays present simplified approximations of the dynamics in natural events. We know very little about how the differences between natural events and computer simulations influence perceptual processing. In practice, we tend to assume that the differences are irrelevant to the questions under study, and that findings with computergenerated stimuli will generalize to natural events. 

College students and children between the ages of 4 and 12 were asked to draw the path a ball would take upon exiting a curved tube. As in previous studies, many subjects erroneously predicted curvilinear paths. However, a clear U-shaped curve was evident in the data: Preschoolers and kindergartners performed as well as college students, whereas school-aged children were more likely to make erroneous predictions. A second study suggested that the youngest children's correct responses could not be attributed to response biases or drawing abilities. This developmental trend is interpreted to mean that the school-aged children are developing intuitive theories of motion that include erroneous principles. The results are related to the “growth errors” found in other cognitive domains and to the historical development of formal theories of motion.

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.

Recent studies have shown that many people demonstrate erroneous beliefs about motion when asked to predict the trajectories of objects. The present experiments examine whether people can select as correct natural trajectories over anomalous ones when presented with the actual on-going event (motion condition) or static representations of the event (no-motion condition). McCloskey’s curved tube problem was used as the event. Results indicate that adults benefit from the motion information in these stimuli, choosing the correct path more often in the motion condition. Men performed better than women in both conditions; this gender effect could not be attributed to formal instruction in physics. Only in the no-motion condition did any men prefer a path which reflected an impetus model of motion. Some women chose a curvilinear path in the motion condition, and in the no-motion condition the curvilinear path was their most often selected alternative. Fifth-grade children demonstrated no effect for gender and their path preferences resembled those of adult males. Children’s responses failed to demonstrate a preference for those curvilinear paths which reflect an impetus-based approach to the problem. Adults’ performance in the no-motion condition was not enhanced by instructions to employ mental imagery of the event.

3 experiments were conducted to examine infant sensitivity at 20, 30, and 36 weeks of age to the 3-dimensional structure of a human form specified through biomechanical motions. All 3 experiments manipulated occlusion information in computer-generated arrays of point-lights moving as if attached to the major joints and head of a person walking. These displays are readily recognized as persons by adults when occlusion information is present, but not when it is absent or inconsistent with the implicit structure of the human body. Converging findings from Experiments 1 and 2 suggested that 36-week-old infants were sensitive to the presence of occlusion information in point-light walker displays; neither 20- nor 30-week-old infants showed any sensitivity to this information. The results of Experiment 3 revealed further that 36-week-old infants were sensitive to whether or not the pattern of occlusion was consistent with the implicit form of the human body, but only when the displays were presented in an upright orientation. These findings are interpreted as suggesting that infants, by 36 weeks of age, are extracting fundamental properties necessary for interpreting a point-light display as a person.

A graphics design program for creating point-light displays of transforming 3-D objects is presented. This program was written for an Apple II microcomputer interfaced to a Texas Instruments TMS 9918A video display processor. In contrast to other 3-D design programs, it uses individual point-lights undergoing circular trajectories as a design primitive. An editor enables the user to enter and edit specific motion parameters for defining the parallel projection of as many as 16 point-lights on the screen. These parameters are then used to calculate and store in an animation list the screen positions of each point-light for each frame. Number of frames to be displayed and display rate are user defined.

Two experiments examined the role of occlusion in reducing perceived multistability in computergenerated point-light walker displays. In Experiment 1, it was found that point-light walker displays lacking occlusion were perceived as multistable and that the addition of occlusion served to reduce this perceived ambiguity. In Experiment 2, it was found that occlusion served two functions in the perception of point-light walker displays: specifying depth order and indicating the presence of implicit occluding forms. These results are discussed in relation to contemporary motion information processing models. All existing models rely solely on the motion and topographical information present in our nonoccluding display; in so doing, these models prove inadequate, since they seek to derive unique perceptions from information seen by observers as being multistable. The findings from the present experiments demonstrate that observers utilize occlusion to reduce multistability, and, thus, rules for processing this information, and/or other forms of constraining information, need to be added to existing motion information processing models.