The human visual system can represent an object's spatial structure with respect to multiple frames of reference. It can also utilize multiple reference frames to mentally transform such representations. Recent studies have shown that performance on some mental transformations is not equivalent: Imagined object rotations tend to be more difficult than imagined viewer rotations. We reviewed several related research domains to understand this discrepancy in terms of the different reference frames associated with each imagined movement. An examination of the mental rotation literature revealed that observers’ difficulties in predicting an object’s rotational outcome may stem from a general deficit with imagining the cohesive rotation of the object’s intrinsic frame. Such judgments are thus more reliant on supplementary information provided by other frames, such as the environmental frame. In contrast, as assessed in motor imagery and other studies, imagined rotations of the viewer’s relative frame are performed cohesively and are thus mostly immune to effects of other frames.

This report addresses the human factors issues related to the reading and comprehension of variable message sign (VMS) messages. A review of the literature was conducted on factors that affect how people read VMSs. Several topics were reviewed. The first topic was literacy. Since reading literacy is not a requirement for obtaining a driver's license, VMS composition should reflect the varied reading competence levels of motorists. It was found that about 25% of Virginians over the age of 16 are weak readers and will likely encounter problems reading VMSs. The second topic addressed how people read. Reading is an interactive process that derives much of its speed and accuracy from implicit knowledge acquired through familiarity. This implies that VMS messages should present familiar, standardized content whenever possible. A review of the literature on warning signs was the third topic. Effective warning signs should have several properties: Short, concise messages are both easier to read and more likely to be read. Signal words, such as CAUTION, are not effective. Finally, areas for further research were identified. Symbolic messages and abbreviations are worthy of further investigation as they have the potential for easy recognition, provided they are familiar to motorists and can be accommodated by the VMS. In addition, although the MUTCD advises angling the VMS away from the roadway to reduce headlight glare, angling the VMS toward the roadway could be desirable for increasing readability. In both these areas, theoretical and practical work is needed. The report recommends that these human factors characteristics and limitations be taken into consideration in the deployment of VMSs and in the composition of their messages.

The present study extended previous findings of geographical slant perception, in which verbal judgments of the incline of hills were greatly overestimated but motoric (haptic) adjustments were much more accurate. In judging slant from memory following a brief or extended time delay, subjects’ verbal judgments were greater than those given when viewing hills. Motoric estimates differed depending on the length of the delay and place of response. With a short delay, motoric adjustments made in the proximity of the hill did not differ from those evoked during perception. When given a longer delay or when taken away from the hill, subjects’ motoric responses increased along with the increase in verbal reports. These results suggest two different memorial influences on action. With a short delay at the hill, memory for visual guidance is separate from the explicit memory informing the conscious response. With short or long delays away from the hill, short-term visual guidance memory no longer persists, and both motor and verbal responses are driven by an explicit representation. These results support recent research involving visual guidance from memory, where actions become influenced by conscious awareness, and provide evidence for communication between the “what” and “how” visual processing systems.

We discuss a two-handed user interface designed to support three-dimesional neurosurgical visualization. By itself, this system is a “point design,” an example of an advanced user interface technique. In this work, we argue that in order to understand why interaction techniques do or do not work, and to suggest possibilities for new techniques, it is important to move beyond point design and to introduce careful scientific measurement of human behavioral principles. In particular, we argue that the common-sense viewpoint that “two hands save time by working in parallel” may not always be an effective way to think about two-handed interface design because the hands do not necessarily work in parallel (there is a structure to two-handed manipulation) and because two hands do more than just save time over one hand (two hands provide the user with more information and can structure how the user thinks about a task). To support these claims, we present an interface design developed in collaboration with neurosurgeons which has undergone extensive informal usability testing, as well as a pair of formal experimental studies which investigate behavioral aspects of two-handed virtual object manipulation. Our hope is that this discussion will help others to apply the lessons in our neurosurgery application to future two-handed user interface designs.

Relative size judgments were collected for two objects at 30.5 m and 23.8 m from the observer in order to assess how performance depends on the relationship between the size of the objects and the eye level of the observer. In three experiments in an indoor hallway and in one experiment outdoors, accuracy was higher for objects in the neighborhood of eye level. We consider these results in the light of two hypotheses. One proposes that observers localize the horizon as a reference for judging relative size, and the other proposes that observers perceive the general neighborhood of the horizon and then employ a height-in-visual-field heuristic. The finding that relative size judgments are best around the horizon implies that information that is independent of distance perception is used in perceiving size.

Virtual Reality (VR) has generated much excitement but little formal proof that it is useful. Because VR interfaces are difficult and expensive to build, the computer graphics community needs to be able to predict which applications will benefit from VR. In this paper, we show that users with a VR interface complete a search task faster than users with a stationary monitor and a hand-based input device. We placed users in the center of the virtual room shown in Figure 1 and told them to look for camouflaged targets. VR users did not do significantly better than desktop users. However, when asked to search the room and conclude if a target existed, VR users were substantially better at determining when they had searched the entire room. Desktop users took 41% more time, re-examining areas they had already searched. We also found a positive transfer of training from VR to stationary displays 

Accuracy in discriminating rigid from nonrigid motion was investigated for orthographic projections of three-dimensional rotating objects. In 3 experiments the hypothesis that magnitudes of angular velocity are misperceived in the kinetic depth effect was tested, and in 4 other experiments the hypothesis that misperceiving angular velocities leads to misperceiving rigidity was tested. The principal findings were (a) the magnitude of perceived angular velocity is derived heuristically as a function of a property of the first-order optic flow called deformation and (b) perceptual performance in discriminating rigid from nonrigid motion is accurate in cases when the variability of the deformations of the individual triplets of points of the stimulus displays favors this interpretation and not accurate in other cases.

We investigate the synergy of the two hands for virtual object manipuhttion. We report results from an experiment which suggest that the two hands together provide sufficient perceptual cues to form a frame of reference which is independent of visual feedback. The same is not true for one hand moving in empty space. Our inteqmtadon is that users may not have to constantly maintain visual attention when both hands can be involved in a manipulation. Our results suggest that using two hands can provide more than just a time savings over one-handed manipulation. llvo hands together provide the user with information which one hand alone cannot. Our results also suggest that using two hands can potentially impact performance at the cognitive level by changing how users think about a task. Since the user can potentially integrate subtasks controlled by each hand without an explicit cost to switch between subtasks, this encourages exploration of the task solution space. Fhmlly, to illustrate why one might expect this to be true, we present a task analysis which helps to rea