Advances in helmet-mounted displays (HMDs) have permitted the design of "see-through" displays in which virtual imagery may be superimposed upon real visual environments. Such displays have numerous potential applications; however, their promise to improve human perception and performance in complex task environments is threatened by numerous technological challenges. Moreover, users of HMDs may be vulnerable to symptoms associated with simulator sickness. The primary objective of this investigation was to assess subjective ratings of simulator sickness as a function of time delay, time on task, and task complexity. Participants attempted to center a reticle over a moving circular target using a see-through HMD while concurrently performing a visual monitoring task displayed on a computer monitor. Results indicated that simulator sickness ratings varied directly with time on task, while performance efficiency and ratings of perceived mental workload were not mediated by this factor. Furthermore, the time delay manipulation that affected performance efficiency and operator workload did not generally influence SSQ ratings. These findings are discussed in terms of their implications for practical implementation of see-through HMDs in multi-task environments.

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An experiment was conducted to determine the extent to which hemispheric specialization is manifested in the performance of tasks in which listeners are required to attend to one of several simultaneously spoken speech communications. Speech intelligibility and response time were measured under factorial combinations of the number of simultaneous talkers, the target talker hemifield, and the spatial arrangement of talkers. Intelligibility was found to be mediated by all of the independent variables. Results are discussed in terms of the design of adaptive spatial audio interfaces for speech communications. Actual or potential applications of this research include the design of adaptive spatial audio interfaces for speech communications.

An experiment was conducted to test whether misalignment effects found when people use maps to determine left and right turns also occur when they make cardinal-direction judgments. Prior research has shown that when an exocentric reference frame, such as a map, is misaligned with a person's egocentric reference frame, people take longer to determine left and right turns. Using both a static task and a dynamic, flight-simulator task, this experiment showed that when exocentric (map) and egocentric reference frames are misaligned, cardinal-direction judgments can be severely impaired, more so than direction-of-turn judgments. Analysis of participants' verbal protocols suggests that people use both mental rotation and non-rotational strategies in making cardinal-direction judgments.

Technological advances in helmet-mounted displays (HMDs) have permitted the design of “see-through” displays in which virtual imagery may be superimposed upon real visual environments. The utility of see-through displays in multitask environments remains uncertain, especially in environments that involve switching one's attention between those tasks represented in the virtual display and those existing in the real world. The present study was designed to assess the effects of a secondary visual monitoring task on performance and workload in a head-slaved tracking task. Participants attempted to center a reticle over a moving circular target using a Kaiser Electronics SimEye 2500 HMD while concurrently performing the visual monitoring task component of the Multi-Attribute Task Battery (MATB; Comstock & Arnegard, 1992), which was displayed on a computer monitor. Task difficulty for the head-slaved tracking task was varied by manipulating time delay. Results are discussed in terms of their implications for practical implementation of see-through HMDs in multi-task environments.