Lawrence J. Hettinger

Modulating postural control to facilitate visual performance

Abstract We explored relations between visual performance and postural control. Variability in postural sway was analyzed in the context of variations in supra-postural visual tasks. We varied target distance (near vs. far) and visual task (inspecting a blank target vs. counting the frequency of letters in a block of text). Variability in postural sway was reduced when participants fixated near targets as opposed to far targets. Also, postural sway during the visual search task was reduced relative to sway during inspection of blank targets. We argue that the search task placed more restrictive constraints on the visual system, and that postural sway was reduced to facilitate visual search. The results support the hypothesis that postural control is not an autonomous system, but is organized as part of an integrated perception–action system. Postural control can be used to improve visual performance.

Visually induced motion sickness in virtual environments

Visually induced motion sickness is a syndrome that occasionally occurs when physically stationary individuals view compelling visual representations of self-motion. It may also occur when detectable lags are present between head movements and recomputation and presentation of the visual display in helmet-mounted displays. The occurrence of this malady is a critical issue for the future development and implementation of virtual environments. Applications of this emerging technology are likely to be compromised to the extent that users experience illness and/or incapacitation. This article presents an overview of what is currently known regarding the relationship between visually specified self-motion in the absence of inertial displacement and resulting illness and perceptual-motor disturbances.

Postural Instability and Motion Sickness in a Fixed-Base Flight Simulator

We evaluated the prediction that postural instability would precede the subjective symptoms of motion sickness in a fixed-base flight simulator. Participants sat in a cockpit in a video projection dome and were exposed to optical flow that oscillated in the roll axis with exposure durations typical of flight simulation. The frequencies of oscillation were those that characterize spontaneous postural sway during stance. Head motion was measured prior to and during exposure to imposed optical flow. Of 14 participants, 6 were classified as motion sick, either during or after exposure to the optical oscillation. Prior to the onset of subjective symptoms, head motion among participants who later became sick was significantly greater than among participants who did not become motion sick. We argue that the results support the postural instability theory of motion sickness. Actual or potential applications include the prevention or mitigation of motion sickness in virtual environments.

Effects of Localized Auditory Information on Visual Target Detection Performance Using a Helmet-Mounted Display

An experiment was conducted to evaluate the effects of localized auditory information on visual target detection performance. Visual targets were presented on either a wide field-of-view dome display or a helmet-mounted display and were accompanied by either localized, nonlocalized, or no auditory information. The addition of localized auditory information resulted in significant increases in target detection performance and significant reductions in workload ratings as compared with conditions in which auditory information was either nonlocalized or absent. Qualitative and quantitative analyses of participants′ head motions revealed that the addition of localized auditory information resulted in extremely efficient and consistent search strategies. Implications for the development and design of multisensory virtual environments are discussed. Actual or potential applications of this research include the use of spatial auditory displays to augment visual information presented in helmet-mounted displays, thereby leading to increases in performance efficiency, reductions in physical and mental workload, and enhanced spatial awareness of objects in the environment.

Vection and visually induced motion sickness: how are they related?

The occurrence of visually induced motion sickness has been frequently linked to the sensation of illusory self-motion (vection), however, the precise nature of this relationship is still not fully understood. To date, it is still a matter of debate as to whether vection is a necessary prerequisite for visually induced motion sickness (VIMS). That is, can there be VIMS without any sensation of self-motion? In this paper, we will describe the possible nature of this relationship, review the literature that addresses this relationship (including theoretical accounts of vection and VIMS), and offer suggestions with respect to operationally defining and reporting these phenomena in future.

Combined effects of auditory and visual cues on the perception of vection

Vection is the illusion of self-motion in the absence of real physical movement. The aim of the present study was to analyze how multisensory inputs (visual and auditory) contribute to the perception of vection. Participants were seated in a stationary position in front of a large, curved projection display and were exposed to a virtual scene that constantly rotated around the yaw-axis, simulating a 360° rotation. The virtual scene contained either only visual, only auditory, or a combination of visual and auditory cues. Additionally, simulated rotation speed (90°/s vs. 60°/s) and the number of sound sources (1 vs. 3) were varied for all three stimulus conditions. All participants were exposed to every condition in a randomized order. Data specific to vection latency, vection strength, the severity of motion sickness (MS), and postural steadiness were collected. Results revealed reduced vection onset latencies and increased vection strength when auditory cues were added to the visual stimuli, whereas MS and postural steadiness were not affected by the presence of auditory cues. Half of the participants reported experiencing auditorily induced vection, although the sensation was rather weak and less robust than visually induced vection. Results demonstrate that the combination of visual and auditory cues can enhance the sensation of vection.

A Theoretical Analysis and Preliminary Investigation of Dynamically Adaptive Interfaces

Adynamically adaptive interface (DAI) is a computer interface that changes the display or control characteristics of a system (or both) in real time. The goal of DAIs is to anticipate informational needs or desires of the user and provide that information without the requirement of an explicit control input by the user. DAIs have the potential to improve overall human-machine system performance if properly designed; they also have a very real potential to degrade performance if they are not properly designed. This article explores both theoretical and practical issues in the design of DAIs. The relation of the DAI concept to decision aiding and automation is discussed, and a theoretical framework for design is outlined.Apreliminary investigation of the DAI design concept was conducted in the domain of aviation (precision, low-level navigation). Nontraditional controls (a force reflecting stick) and displays (a configural flight director) were developed to support performance at the task. A standard interface (conventional controls and displays), a candidate interface (alternative controls and displays), and an adaptive interface (dynamically alternating between the standard and candidate displays) were evaluated. The results indicate that significant performance advantages in the quality of route navigation were obtained with the candidate and adaptive interfaces relative to the standard interface; no significant differences between the candidate and adaptive interfaces were obtained. The implications of these results are discussed, with special emphasis on their relation to fundamental challenges that must be met for the DAI concept to be a viable design alternative.

Multisensory Interface Design for Complex Task Domains: Replacing Information Overload With Meaning in Tactical Crew Stations

Modern aerial combat represents a highly complex task domain that imposes many significant challenges on aviators. In modern cockpits there are more sources of dynamic information than any single pilot has the ability to attend to, let alone comprehend, all at once. As technological developments lead to the deployment of new weapons systems, the future aerial battlefield will inevitably yield increased levels of complexity. A significant challenge for cockpit designers is to devise pilot-vehicle interfaces that take full advantage of the parallel information extraction capabilities of humans through the use of integrated multisensory displays. This article describes an approach to multisensory display development that uses human performance evaluations as a design tool, and concludes with a description of a multisensory crew station designed by an interdisciplinary team.

Demonstrating the Potential for Dynamic Auditory Stimulation to Contribute to Motion Sickness

Auditory cues can create the illusion of self-motion (vection) in the absence of visual or physical stimulation. The present study aimed to determine whether auditory cues alone can also elicit motion sickness and how auditory cues contribute to motion sickness when added to visual motion stimuli. Twenty participants were seated in front of a curved projection display and were exposed to a virtual scene that constantly rotated around the participants vertical axis. The virtual scene contained either visual-only, auditory-only, or a combination of corresponding visual and auditory cues. All participants performed all three conditions in a counterbalanced order. Participants tilted their heads alternately towards the right or left shoulder in all conditions during stimulus exposure in order to create pseudo-Coriolis effects and to maximize the likelihood for motion sickness. Measurements of motion sickness (onset, severity), vection (latency, strength, duration), and postural steadiness (center of pressure) were recorded. Results showed that adding auditory cues to the visual stimuli did not, on average, affect motion sickness and postural steadiness, but it did reduce vection onset times and increased vection strength compared to pure visual or pure auditory stimulation. Eighteen of the 20 participants reported at least slight motion sickness in the two conditions including visual stimuli. More interestingly, six participants also reported slight motion sickness during pure auditory stimulation and two of the six participants stopped the pure auditory test session due to motion sickness. The present study is the first to demonstrate that motion sickness may be caused by pure auditory stimulation, which we refer to as “auditorily induced motion sickness”.

Visual Display Factors Contributing to Simulator Sickness

The history of research on visually-induced illusory self motion, or vection, has demonstrated that in many instances observers have experienced disturbances similar to those of motion sickness. Visual displays in flight simulators may also produce the experience of vection, and illusions of self motion are likely to become more common with the increased use of wide field-of-view presentations of realistic imagery. Many of the disturbances observed in laboratory studies of vection have also been found in simulators, and are likely to become more common. This paper presents a background to the study of visual-vestibular disturbances associated with illusory self motion in flight simulators, and an overview of current experimental efforts aimed at identifying the causal factors.