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

Inducing unstable walking conditions through visual and auditory stimuli

[Purpose] Falls can significantly affect elderly individuals. However, most current methods used to detect and analyze high-risk conditions make use of simulated falling movements for data collection, which may not accurately represent actual falls. The present study aimed to induce natural falls using visual and auditory stimuli to create unstable walking conditions. [Participants and Methods] Two experiments were performed. The first experiment focused on inducing unstable walking using visual stimuli; whereas, the second experiment combined visual and auditory stimuli. To investigate the effects of stimuli on the induction of unstable walking, our results were compared with those of normal walking conditions. In addition, the two experimental conditions were compared to identify the most effective stimuli. [Results] Both experiments revealed a decrease in step length, an increase in step time and width, and an increase in the coefficient of variation of measurements, indicating an induced walking pattern with a higher risk of falls. Furthermore, combining visual and auditory stimuli caused deterioration of inter-limb coordination, as observed through an increased phase coordination index, thus resulting in further instability during walking. [Conclusion] Visual and auditory stimuli induced unstable walking. In particular, the combination of visual and auditory stimuli with a 0.8-s rhythm increased instability.

A virtual reality study investigating the train illusion

The feeling of self-movement that occurs in the absence of physical motion is often referred to as vection, which is commonly exemplified using the train illusion analogy (TIA). Limited research exists on whether the TIA accurately exemplifies the experience of vection in virtual environments (VEs). Few studies complemented their vection research with participants' qualitative feedback or by recording physiological responses, and most studies used stimuli that contextually differed from the TIA. We investigated whether vection is experienced differently in a VE replicating the TIA compared to a VE depicting optic flow by recording subjective and physiological responses. Additionally, we explored participants' experience through an open question survey. We expected the TIA environment to induce enhanced vection compared to the optic flow environment. Twenty-nine participants were visually and audibly immersed in VEs that either depicted optic flow or replicated the TIA. Results showed optic flow elicited more compelling vection than the TIA environment and no consistent physiological correlates to vection were identified. The post-experiment survey revealed discrepancies between participants' quantitative and qualitative feedback. Although the dynamic content may outweigh the ecological relevance of the stimuli, it was concluded that more qualitative research is needed to understand participants' vection experience in VEs.

Caloric vestibular stimulation induces vestibular circular vection even with a conflicting visual display presented in a virtual reality headset

This study explored visual-vestibular sensory integration when the vestibular system receives self-motion information using caloric irrigation. The objectives of this study were to (1) determine if measurable vestibular circular vection can be induced in healthy participants using caloric vestibular stimulation and (2) determine if a conflicting visual display could impact vestibular vection. In Experiment 1 (E1), participants had their eyes closed. Air caloric vestibular stimulation cooled the endolymph fluid of the horizontal semi-circular canal inducing vestibular circular vection. Participants reported vestibular circular vection with a potentiometer knob that measured circular vection direction, speed, and duration. In Experiment 2 (E2), participants viewed a stationary display in a virtual reality headset that did not signal self-motion while receiving caloric vestibular stimulation. This produced a visual-vestibular conflict. Participants indicated clockwise vection in the left ear and counter-clockwise vection in right ear in a significant proportion of trials in E1 and E2. Vection was significantly slower and shorter in E2 compared to E1. E2 results demonstrated that during visual-vestibular conflict, visual and vestibular cues are used to determine self-motion rather than one system overriding the other. These results are consistent with optimal cue integration hypothesis.

Something in the Sway: Effects of the Shepard-Risset Glissando on Postural Activity and Vection

This study investigated claims of disrupted equilibrium when listening to the Shepard-Risset glissando (which creates an auditory illusion of perpetually ascending/descending pitch). During each trial, 23 participants stood quietly on a force plate for 90 s with their eyes either open or closed (30 s pre-sound, 30 s of sound and 30 s post-sound). Their centre of foot pressure (CoP) was continuously recorded during the trial and a verbal measure of illusory self-motion (i.e., vection) was obtained directly afterwards. As expected, vection was stronger during Shepard-Risset glissandi than during white noise or phase-scrambled auditory control stimuli. Individual differences in auditorily evoked postural sway (observed during sound) were also found to predict the strength of this vection. Importantly, the patterns of sway induced by Shepard-Risset glissandi differed significantly from those during our auditory control stimuli - but only in terms of their temporal dynamics. Since significant sound type differences were not seen in terms of sway magnitude, this stresses the importance of investigating the temporal dynamics of sound-posture interactions.

Enhanced vection in older adults: Evidence for age-related effects in multisensory vection experiences

The illusion of self-motion (vection) is a multisensory phenomenon elicited by visual, auditory, tactile, or other sensory cues. Aging is often associated with changes in sensory acuity, visual motion perception, and multisensory integration, processes which may influence vection perception. However, age-related differences in vection have received little study to date. Thus, the objective of the present study was to investigate age-related differences in vection during multisensory stimulation. Nineteen younger adults and 19 older adults were exposed to rotating visual, auditory, and tactile stimuli (separately or in combination) at a speed of 45°/s inside a VR laboratory inducing circular vection. The size of the field-of-view (FOV) was large (240°), medium (75°), small (30°), or contained no visuals. Vection intensity and duration were reported verbally after each trial. Overall, older adults experienced significantly stronger and longer vection compared to younger adults. Additionally, there were main effects of FOV and sensory cues, such that larger FOVs and the presence of auditory and tactile stimulation increased vection ratings for both age groups. These findings support the idea that vection is a multisensory experience that can be elicited by visual, auditory, and tactile stimuli and demonstrates these effects for the first time in older adults.

Multisensory Effects on Illusory Self-Motion (Vection): the Role of Visual, Auditory, and Tactile Cues

A critical component to many immersive experiences in virtual reality (VR) is vection, defined as the illusion of self-motion. Traditionally, vection has been described as a visual phenomenon, but more recent research suggests that vection can be influenced by a variety of senses. The goal of the present study was to investigate the role of multisensory cues on vection by manipulating the availability of visual, auditory, and tactile stimuli in a VR setting. To achieve this, 24 adults (Mage = 25.04) were presented with a rotating stimulus aimed to induce circular vection. All participants completed trials that included a single sensory cue, a combination of two cues, or all three cues presented together. The size of the field of view (FOV) was manipulated across four levels (no-visuals, small, medium, full). Participants rated vection intensity and duration verbally after each trial. Results showed that all three sensory cues induced vection when presented in isolation, with visual cues eliciting the highest intensity and longest duration. The presence of auditory and tactile cues further increased vection intensity and duration compared to conditions where these cues were not presented. These findings support the idea that vection can be induced via multiple types of sensory inputs and can be intensified when multiple sensory inputs are combined.

Effects of stereopsis on vection, presence and cybersickness in head-mounted display (HMD) virtual reality

Stereopsis provides critical information for the spatial visual perception of object form and motion. We used virtual reality as a tool to understand the role of global stereopsis in the visual perception of self-motion and spatial presence using virtual environments experienced through head-mounted displays (HMDs). Participants viewed radially expanding optic flow simulating different speeds of self-motion in depth, which generated the illusion of self-motion in depth (i.e., linear vection). Displays were viewed with the head either stationary (passive radial flow) or laterally swaying to the beat of a metronome (active conditions). Multisensory conflict was imposed in active conditions by presenting displays that either: (i) compensated for head movement (active compensation condition), or (ii) presented pure radial flow with no compensation during head movement (active no compensation condition). In Experiment 1, impairing stereopsis by anisometropic suppression in healthy participants generated declines in reported vection strength, spatial presence and severity of cybersickness. In Experiment 2, vection and presence ratings were compared between participants with and without clinically-defined global stereopsis. Participants without global stereopsis generated impaired vection and presence similarly to those found in Experiment 1 by subjects with induced stereopsis impairment. We find that reducing global stereopsis can have benefits of reducing cybersickness, but has adverse effects on aspects of self-motion perception in HMD VR.

The effect of water immersion on vection in virtual reality

Research about vection (illusory self-motion) has investigated a wide range of sensory cues and employed various methods and equipment, including use of virtual reality (VR). However, there is currently no research in the field of vection on the impact of floating in water while experiencing VR. Aquatic immersion presents a new and interesting method to potentially enhance vection by reducing conflicting sensory information that is usually experienced when standing or sitting on a stable surface. This study compares vection, visually induced motion sickness, and presence among participants experiencing VR while standing on the ground or floating in water. Results show that vection was significantly enhanced for the participants in the Water condition, whose judgments of self-displacement were larger than those of participants in the Ground condition. No differences in visually induced motion sickness or presence were found between conditions. We discuss the implication of this new type of VR experience for the fields of VR and vection while also discussing future research questions that emerge from our findings.

The role of cognitive factors and personality traits in the perception of illusory self-motion (vection)

Vection is a perceptual phenomenon that describes the visually induced subjective sensation of self-motion in the absence of physical motion. Previous research has discussed the potential involvement of top-down cognitive mechanisms on vection. Here, we quantified how cognitive manipulations such as contextual information (i.e., expectation) and plausibility (i.e., chair configuration) alter vection. We also explored how individual traits such as field dependence, depersonalization, anxiety, and social desirability might be related to vection. Fifty-one healthy adults were exposed to an optic flow stimulus that consisted of horizontally moving black-and-white bars presented on three adjacent monitors to generate circular vection. Participants were divided into three groups and given experimental instructions designed to induce either strong, weak, or no expectation with regard to the intensity of vection. In addition, the configuration of the chair (rotatable or fixed) was modified during the experiment. Vection onset time, duration, and intensity were recorded. Results showed that expectation altered vection intensity, but only when the chair was in the rotatable configuration. Positive correlations for vection measures with field dependence and depersonalization, but no sex-related effects were found. Our results show that vection can be altered by cognitive factors and that individual traits can affect the perception of vection, suggesting that vection is not a purely perceptual phenomenon, but can also be affected by top-down mechanisms.

Neuropsychological Approaches to Visually-Induced Vection: an Overview and Evaluation of Neuroimaging and Neurophysiological Studies

Moving visual stimuli can elicit the sensation of self-motion in stationary observers, a phenomenon commonly referred to as vection. Despite the long history of vection research, the neuro-cognitive processes underlying vection have only recently gained increasing attention. Various neuropsychological techniques such as functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) have been used to investigate the temporal and spatial characteristics of the neuro-cognitive processing during vection in healthy participants. These neuropsychological studies allow for the identification of different neuro-cognitive correlates of vection, which (a) will help to unravel the neural basis of vection and (b) offer opportunities for applying vection as a tool in other research areas. The purpose of the current review is to evaluate these studies in order to show the advances in neuropsychological vection research and the challenges that lie ahead. The overview of the literature will also demonstrate the large methodological variability within this research domain, limiting the integration of results. Next, we will summarize methodological considerations and suggest helpful recommendations for future vection research, which may help to enhance the comparability across neuropsychological vection studies.

Perceptual Postural Imbalance and Visual Vertigo

PURPOSE OF REVIEW

Disorders of posture and balance cause significant patient morbidity, with reduction of quality of life as patients refrain from critical activities of daily living such as walking outside the home and driving. This review describes recent efforts to characterize visual disorders that interact with the neural integrators of positional maintenance and emerging therapies for these disorders.

RECENT FINDINGS

Abnormalities of gait and body position sense may be unrecognized by patients but are correlated with focal neurological injury (stroke). Patients with traumatic brain injury can exhibit visual vertigo despite otherwise normal visual functioning. The effect of visual neglect on posture and balance, even in the absence of a demonstrable visual field defect, has been characterized quantitatively through gait analysis and validates the potential therapeutic value of prism treatment in some patients. In addition, the underlying neural dysfunction in visual vertigo has been explored further using functional imaging, and these observations may allow discrimination of patients with structural causes from those whose co-morbid psychosocial disorders may be primarily contributory.

Echo-acoustic and optic flow interact in bats

Echolocating bats are known to fly and forage in complete darkness using the echoes of their actively emitted calls to navigate and to detect prey. However, under dim light conditions many bats can also rely on vision. Many flying animals have been shown to navigate by optic flow information, and recently, bats were shown to exploit echo-acoustic flow to navigate through dark habitats. Here we show for the bat Phyllostomus discolor that in lighted habitats where self-motion induced optic flow is strong, optic and echo-acoustic flow interact in their efficiency to guide navigation. Echo-acoustic flow showed a surprisingly strong effect compared to optic flow. We thus demonstrate multimodal interaction between two far-ranging spatial senses, vision and echolocation, available in this combination almost exclusively for bats and toothed whales. Our results highlight the importance of merging information from different sensory systems in a sensory-specialist animal to successfully navigate and hunt under difficult conditions.

Unidirectional monosynaptic connections from auditory areas to the primary visual cortex in the marmoset monkey

Until the late twentieth century, it was believed that different sensory modalities were processed by largely independent pathways in the primate cortex, with cross-modal integration only occurring in specialized polysensory areas. This model was challenged by the finding that the peripheral representation of the primary visual cortex (V1) receives monosynaptic connections from areas of the auditory cortex in the macaque. However, auditory projections to V1 have not been reported in other primates. We investigated the existence of direct interconnections between V1 and auditory areas in the marmoset, a New World monkey. Labelled neurons in auditory cortex were observed following 4 out of 10 retrograde tracer injections involving V1. These projections to V1 originated in the caudal subdivisions of auditory cortex (primary auditory cortex, caudal belt and parabelt areas), and targeted parts of V1 that represent parafoveal and peripheral vision. Injections near the representation of the vertical meridian of the visual field labelled few or no cells in auditory cortex. We also placed 8 retrograde tracer injections involving core, belt and parabelt auditory areas, none of which revealed direct projections from V1. These results confirm the existence of a direct, nonreciprocal projection from auditory areas to V1 in a different primate species, which has evolved separately from the macaque for over 30 million years. The essential similarity of these observations between marmoset and macaque indicate that early-stage audiovisual integration is a shared characteristic of primate sensory processing.

The search for instantaneous vection: An oscillating visual prime reduces vection onset latency

Typically it takes up to 10 seconds or more to induce a visual illusion of self-motion (“vection”). However, for this vection to be most useful in virtual reality and vehicle simulation, it needs to be induced quickly, if not immediately. This study examined whether vection onset latency could be reduced towards zero using visual display manipulations alone. In the main experiments, visual self-motion simulations were presented to observers via either a large external display or a head-mounted display (HMD). Priming observers with visually simulated viewpoint oscillation for just ten seconds before the main self-motion display was found to markedly reduce vection onset latencies (and also increase ratings of vection strength) in both experiments. As in earlier studies, incorporating this simulated viewpoint oscillation into the self-motion displays themselves was also found to improve vection. Average onset latencies were reduced from 8-9s in the no oscillating control condition to as little as 4.6 s (for external displays) or 1.7 s (for HMDs) in the combined oscillation condition (when both the visual prime and the main self-motion display were oscillating). As these display manipulations did not appear to increase the likelihood or severity of motion sickness in the current study, they could possibly be used to enhance computer generated simulation experiences and training in the future, at no additional cost.

An Illusory Contour Can Facilitate Visually Induced Self-Motion Perception

Uniform motion of a visual stimulus induces an illusory perception of the observer's self-body moving in the opposite direction (vection). The present study investigated whether vertical illusory contours can affect horizontal translational vection using abutting-line stimulus. The stimulus consisted of a number of horizontal line segments that moved horizontally at a constant speed. A group of vertically aligned segments created a 'striped column', while line segments in adjoining columns were shifted vertically to make a slight gap between them. In the illusory contour condition, the end points of the segments within the column were horizontally aligned to generate vertical illusory contours. In the condition with no illusory contour, these end points were not aligned within the column so that the illusory contour was not perceived. In the current study, 11 participants performed this experiment, and it was shown that stronger vection was induced in the illusory contour condition than in the condition with no illusory contour. The results of the current experiment provide novel evidence suggesting that non-luminance-defined visual features have a facilitative effect on visual self-motion perception.

The Oscillating Potential Model of Visually Induced Vection

Visually induced illusions of self-motion are often referred to as vection. This article developed and tested a model of responding to visually induced vection. We first constructed a mathematical model based on well-documented characteristics of vection and human behavioral responses to this illusion. We then conducted 10,000 virtual trial simulations using this Oscillating Potential Vection Model (OPVM). OPVM was used to generate simulated vection onset, duration, and magnitude responses for each of these trials. Finally, we compared the properties of OPVM's simulated vection responses with real responses obtained in seven different laboratory-based vection experiments. The OPVM output was found to compare favorably with the empirically obtained vection data.

The Shepard-Risset glissando: music that moves you

Sounds are thought to contribute to the perceptions of self-motion, often via higher-level, cognitive mechanisms. This study examined whether illusory self-motion (i.e. vection) could be induced by auditory metaphorical motion stimulation (without providing any spatialized or low-level sensory information consistent with self-motion). Five different types of auditory stimuli were presented in mono to our 20 blindfolded, stationary participants (via a loud speaker array): (1) an ascending Shepard-Risset glissando; (2) a descending Shepard-Risset glissando; (3) a combined Shepard-Risset glissando; (4) a combined-adjusted (loudness-controlled) Shepard-Risset glissando; and (5) a white-noise control stimulus. We found that auditory vection was consistently induced by all four Shepard-Risset glissandi compared to the white-noise control. This metaphorical auditory vection appeared similar in strength to the vection induced by the visual reference stimulus simulating vertical self-motion. Replicating past visual vection findings, we also found that individual differences in postural instability appeared to significantly predict auditory vection strength ratings. These findings are consistent with the notion that auditory contributions to self-motion perception may be predominantly due to higher-level cognitive factors.

Effect of Different Display Types on Vection and Its Interaction With Motion Direction and Field Dependence

Illusory self-motion (vection) can be generated by visual stimulation. The purpose of the present study was to compare behavioral vection measures including intensity ratings, duration, and onset time across different visual display types. Participants were exposed to a pattern of alternating black-and-white horizontal or vertical bars that moved either in vertical or horizontal direction, respectively. Stimuli were presented on four types of displays in randomized order: (a) large field of view dome projection, (b) combination of three computer screens, (c) single computer screen, (d) large field of view flat projection screen. A Computer Rod and Frame Test was used to measure field dependence, a cognitive style indicating the person’s tendency to rely on external cues (i.e., field dependent) or internal cues (i.e., field independent) with respect to the perception of one’s body position in space. Results revealed that all four displays successfully generated at least moderately strong vection. However, shortest vection onset, longest vection duration, and strongest vection intensity showed for the dome projection and the combination of three screens. This effect was further pronounced in field independent participants, indicating that field dependence can alter vection.

Cybersickness without the wobble: Experimental results speak against postural instability theory

It has been suggested that postural instability is necessary for cybersickness to occur. Seated and standing subjects used a head-mounted display to view a virtual tunnel that rotated about their line of sight. We found that the offset direction of perceived vertical settings matched the direction of the tunnel's rotation, so replicating earlier findings. Increasing rotation speed caused cybersickness to increase, but had no significant impact on perceived vertical settings. Postural sway during rotation was similar to postural sway during rest. While a minority of subjects exhibited postural sway in response to the onset of tunnel rotation, the majority did not. Furthermore, cybersickness increased with rotation speed similarly for the seated and standing conditions. Finally, subjects with greater levels of cybersickness exhibited less variation in postural sway. These results lead us to conclude that the link between postural instability and cybersickness is a weak one in the present experiment.

Age Differences in Visual-Auditory Self-Motion Perception during a Simulated Driving Task

Recent evidence suggests that visual-auditory cue integration may change as a function of age such that integration is heightened among older adults. Our goal was to determine whether these changes in multisensory integration are also observed in the context of self-motion perception under realistic task constraints. Thus, we developed a simulated driving paradigm in which we provided older and younger adults with visual motion cues (i.e., optic flow) and systematically manipulated the presence or absence of congruent auditory cues to self-motion (i.e., engine, tire, and wind sounds). Results demonstrated that the presence or absence of congruent auditory input had different effects on older and younger adults. Both age groups demonstrated a reduction in speed variability when auditory cues were present compared to when they were absent, but older adults demonstrated a proportionally greater reduction in speed variability under combined sensory conditions. These results are consistent with evidence indicating that multisensory integration is heightened in older adults. Importantly, this study is the first to provide evidence to suggest that age differences in multisensory integration may generalize from simple stimulus detection tasks to the integration of the more complex and dynamic visual and auditory cues that are experienced during self-motion.

Podokinetic circular vection: characteristics and interaction with optokinetic circular vection

Stabilising horizontal body orientation in space without sight on a rotating platform by holding to a stationary structure and circular 'treadmill' stepping in the opposite direction can elicit an illusion of self-turning in space (Bles and Kapteyn in Agressologie 18:325-328, 1977). Because this illusion is analogous to the well-known illusion of optokinetic circular vection (oCV), we call it 'podokinetic circular vection' (pCV) here. Previous studies using eccentric stepping on a path tangential to the rotation found that pCV was always contraversive relative to platform rotation. In contrast, when our subjects stepped at the centre of rotation about their vertical axis, we observed an inverted, ipsiversive pCV as a reproducible trait in many of our subjects. This ipCV occurred at the same latency as the pCV of subjects reporting the actually expected contraversive direction, but had lower gain. In contrast to pCV, the nystagmus accompanying circular treadmill stepping had the same direction in all individuals (slow phase in the direction of platform motion). The direction of an individual's pCV predicted the characteristics of the CV resulting from combined opto- and podokinetic stimulation (circular treadmill stepping while viewing a pattern rotating together with the platform): in individuals with contraversive pCV, latency shortened and both gain and felt naturalness increased in comparison with pure oCV, whereas the opposite (longer latency, reduced gain and naturalness) occurred in individuals with ipCV. Taken together, the reproducibility of ipCV, the constant direction of nystagmus and the fact that pCV direction predicts the outcome of combined stimulation suggest that ipCV is an individual trait of many subjects during compensatory stepping at the centre of rotation. A hypothetical model is presented of how ipCV possibly could arise.

Pathophysiology and treatment of motion sickness

PURPOSE OF REVIEW

Motion sickness remains bothersome in conventional transport and is an emerging hazard in visual information technologies. Treatment remains unsatisfactory but advances in brain imaging, neurophysiology, and neuropharmacology may provide insights into more effective drug and behavioural management. We review these major developments.

RECENT FINDINGS

Recent progress has been in identifying brain mechanisms and loci associated with motion sickness and nausea per se. The techniques have included conventional neurophysiology, pathway mapping, and functional MRI, implicating multiple brain regions including cortex, brainstem, and cerebellum. Understanding of the environmental and behavioural conditions provocative of and protective against motion sickness and how vestibular disease may sensitize to motion sickness has increased. The problem of nauseogenic information technology has emerged as a target for research, motivated by its ubiquitous applications. Increased understanding of the neurophysiology and brain regions associated with motion sickness may provide for more effective medication in the future. However, the polysymptomatic nature of motion sickness, high interindividual variability, and the extensive brain regions involved may preclude a single, decisive treatment.

SUMMARY

Motion sickness is an emerging hazard in information technologies. Adaptation remains the most effective countermeasure together with established medications, notably scopolamine and antihistamines. Neuropharmacological investigations may provide more effective medication in the foreseeable future.

Human Vection Perception Using Inertial Nulling and Certainty Estimation: The Effect of Migraine History

Vection is an illusory perception of self-motion that can occur when visual motion fills the majority of the visual field. This study examines the effect of the duration of visual field movement (VFM) on the perceived strength of self-motion using an inertial nulling (IN) and a magnitude estimation technique based on the certainty that motion occurred (certainty estimation, CE). These techniques were then used to investigate the association between migraine diagnosis and the strength of perceived vection. Visual star-field stimuli consistent with either looming or receding motion were presented for 1, 4, 8 or 16s. Subjects reported the perceived direction of self-motion during the final 1s of the stimulus. For the IN method, an inertial nulling motion was delivered during this final 1s of the visual stimulus, and subjects reported the direction of perceived self-motion during this final second. The magnitude of inertial motion was varied adaptively to determine the point of subjective equality (PSE) at which forward or backward responses were equally likely. For the CE trials the same range of VFM was used but without inertial motion and subjects rated their certainty of motion on a scale of 0–100. PSE determined with the IN technique depended on direction and duration of visual motion and the CE technique showed greater certainty of perceived vection with longer VFM duration. A strong correlation between CE and IN techniques was present for the 8s stimulus. There was appreciable between-subject variation in both CE and IN techniques and migraine was associated with significantly increased perception of self-motion by CE and IN at 8 and 16s. Together, these results suggest that vection may be measured by both CE and IN techniques with good correlation. The results also suggest that susceptibility to vection may be higher in subjects with a history of migraine.

The Use of Virtual Reality in Psychology: A Case Study in Visual Perception

Recent proliferation of available virtual reality (VR) tools has seen increased use in psychological research. This is due to a number of advantages afforded over traditional experimental apparatus such as tighter control of the environment and the possibility of creating more ecologically valid stimulus presentation and response protocols. At the same time, higher levels of immersion and visual fidelity afforded by VR do not necessarily evoke presence or elicit a "realistic" psychological response. The current paper reviews some current uses for VR environments in psychological research and discusses some ongoing questions for researchers. Finally, we focus on the area of visual perception, where both the advantages and challenges of VR are particularly salient.

Effects of auditory information on self-motion perception during simultaneous presentation of visual shearing motion

Recent studies have found that self-motion perception induced by simultaneous presentation of visual and auditory motion is facilitated when the directions of visual and auditory motion stimuli are identical. They did not, however, examine possible contributions of auditory motion information for determining direction of self-motion perception. To examine this, a visual stimulus projected on a hemisphere screen and an auditory stimulus presented through headphones were presented separately or simultaneously, depending on experimental conditions. The participant continuously indicated the direction and strength of self-motion during the 130-s experimental trial. When the visual stimulus with a horizontal shearing rotation and the auditory stimulus with a horizontal one-directional rotation were presented simultaneously, the duration and strength of self-motion perceived in the opposite direction of the auditory rotation stimulus were significantly longer and stronger than those perceived in the same direction of the auditory rotation stimulus. However, the auditory stimulus alone could not sufficiently induce self-motion perception, and if it did, its direction was not consistent within each experimental trial. We concluded that auditory motion information can determine perceived direction of self-motion during simultaneous presentation of visual and auditory motion information, at least when visual stimuli moved in opposing directions (around the yaw-axis). We speculate that the contribution of auditory information depends on the plausibility and information balance of visual and auditory information.

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.

Future challenges for vection research: definitions, functional significance, measures, and neural bases

This paper discusses four major challenges facing modern vection research. Challenge 1 (Defining Vection) outlines the different ways that vection has been defined in the literature and discusses their theoretical and experimental ramifications. The term vection is most often used to refer to visual illusions of self-motion induced in stationary observers (by moving, or simulating the motion of, the surrounding environment). However, vection is increasingly being used to also refer to non-visual illusions of self-motion, visually mediated self-motion perceptions, and even general subjective experiences (i.e., “feelings”) of self-motion. The common thread in all of these definitions is the conscious subjective experience of self-motion. Thus, Challenge 2 (Significance of Vection) tackles the crucial issue of whether such conscious experiences actually serve functional roles during self-motion (e.g., in terms of controlling or guiding the self-motion). After more than 100 years of vection research there has been surprisingly little investigation into its functional significance. Challenge 3 (Vection Measures) discusses the difficulties with existing subjective self-report measures of vection (particularly in the context of contemporary research), and proposes several more objective measures of vection based on recent empirical findings. Finally, Challenge 4 (Neural Basis) reviews the recent neuroimaging literature examining the neural basis of vection and discusses the hurdles still facing these investigations.

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 participant's 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”.