Cybersickness: a multisensory integration perspective

In the past decade, there has been a rapid advance in Virtual Reality (VR) technology. Key to the user’s VR experience are multimodal interactions involving all senses. The human brain must integrate real-time vision, hearing, vestibular and proprioceptive inputs to produce the compelling and captivating feeling of immersion in a VR environment. A serious problem with VR is that users may develop symptoms similar to motion sickness, a malady called cybersickness. At present the underlying cause of cybersickness is not yet fully understood. Cybersickness may be due to a discrepancy between the sensory signals which provide information about the body’s orientation and motion: in many VR applications, optic flow elicits an illusory sensation of motion which tells users that they are moving in a certain direction with certain acceleration. However, since users are not actually moving, their proprioceptive and vestibular organs provide no cues of self-motion. These conflicting signals may lead to sensory discrepancies and eventually cybersickness. Here we review the current literature to develop a conceptual scheme for understanding the neural mechanisms of cybersickness. We discuss an approach to cybersickness based on sensory cue integration, focusing on the dynamic re-weighting of visual and vestibular signals for self-motion

Vestibular cognition: state-of-the-art and future directions

Vestibular information has been traditionally considered as a specialized input for basic orienting behaviours, such as oculo-motor adjustments, postural control and gaze orientation. However, in the past two decades a widespread vestibular network in the human brain has been identified, that goes far beyond the low-level reflex circuits emphasized by earlier work. Because this vestibular cortical network is so widely distributed, it could, in principle, impact multiple neurocognitive functions in health and disease. This paper focuses on the relations between vestibular input, vestibular networks, and vestibular interventions by providing the authors’ personal viewpoint on the state-of-the-art of vestibular cognitive neuropsychology, and its potential relevance for neurorehabilitation

The vestibular body: vestibular contributions to bodily representations

Vestibular signals are integrated with signals from other sensory modalities. This convergence could reflect an important mechanism for maintaining the perception of the body. Here we review the current literature in order to develop a framework for understanding how the vestibular system contributes to body representation. According to recent models, we distinguish between three processes for body representation, and we look at whether vestibular signals might influence each process. These are (i) somatosensation, the primary sensory processing of somatic stimuli, (ii) somatoperception, the processes of constructing percepts and experiences of somatic objects and events and (iii) somatorepresentation, the knowledge about the body as a physical object in the world. Vestibular signals appear to contribute to all three levels in this model of body processing. Thus, the traditional view of the vestibular system as a low-level, dedicated orienting module tends to underestimate the pervasive role of vestibular input in bodily self-awareness

Vestibular–somatosensory interactions: a mechanism in search of a function?

No unimodal vestibular cortex has been identified in the human brain. Rather, vestibular inputs are strongly integrated with signals from other sensory modalities, such as vision, touch and proprioception. This convergence could reflect an important mechanism for maintaining a perception of the body, including individual body parts, relative to the rest of the environment. Neuroimaging, electrophysiological and psychophysical studies showed evidence for multisensory interactions between vestibular and somatosensory signals. However, no convincing overall theoretical framework has been proposed for vestibular–somatosensory interactions, and it remains unclear whether such percepts are by-products of neural convergence, or a functional multimodal integration. Here we review the current literature on vestibular–multisensory interactions in order to develop a framework for understanding the functions of such multimodal interaction. We propose that the target of vestibular–somatosensory interactions is a form of self-representation

Transforming the Thermal Grill Effect by crossing the fingers

The relation between pain perception and spatial representation of the body is poorly understood. In the thermal grill illusion (TGI), alternating non-noxious warm and cold temperatures cause a paradoxical, sometimes painful, sensation of burning heat [1]. We combined thermal grill stimulation with crossing the fingers to investigate whether nociceptively mediated sensation depends on the somatotopic or spatiotopic configuration of thermal inputs. We stimulated the index, middle, and ring fingers when the middle finger either was or was not crossed over the index to generate “warm-cold-warm” patterns in either somatotopic or spatiotopic coordinates. Participants adjusted a temperature delivered to the other hand until it matched their perception of the cold target finger (index or middle). We found significant temperature overestimation when the target was central within the spatial configuration (warm-cold-warm) compared to when it was peripheral (cold-warm-warm). Crucially, this effect depended on the spatiotopic configuration of thermal inputs, but it was independent of the finger posture and present for both index and middle target fingers—the thermal grill effect for the middle finger was abolished when it was crossed over the index to adopt a spatiotopically peripheral position, while the same effect was newly generated for the index finger by the same postural change. Our results suggest that the locations of multiple stimuli are remapped into external space as a group; nociceptively mediated sensations depended not on the body posture, but rather on the external spatial configuration formed by the pattern of thermal stimuli in each posture

Vestibular stimulation makes people more egocentric

International audienc

Gravity modulates behaviour control strategy

Human behaviour is a trade-off between exploitation of familiar resources and exploration of new ones. In a challenging environment—such as outer space—making the correct decision is vital. On Earth, gravity is always there, and is an important reference for behaviour. Thus, altered gravitational signals may affect behaviour control strategies. Here, we investigated whether changing the body’s orientation to the gravitational vector would modulate the balance between routine and novel behaviour. Participants completed a random number generation task while upright or supine. We found decreased randomness when participants were supine. In particular, the degree of equiprobability of pairs of consecutive responses was reduced in the supine orientation. Online gravitational signals may shape the balance between exploitation and exploration, in favour of more stereotyped and routine responses

Multisensory interactions between vestibular, visual and somatosensory signals

Vestibular inputs are constantly processed and integrated with signals from other sensory modalities, such as vision and touch. The multiply-connected nature of vestibular cortical anatomy led us to investigate whether vestibular signals could participate in a multi-way interaction with visual and somatosensory perception. We used signal detection methods to identify whether vestibular stimulation might interact with both visual and somatosensory events in a detection task. Participants were instructed to detect near-threshold somatosensory stimuli that were delivered to the left index finger in one half of experimental trials. A visual signal occurred close to the finger in half of the trials, independent of somatosensory stimuli. A novel Near infrared caloric vestibular stimulus (NirCVS) was used to artificially activate the vestibular organs. Sham stimulations were used to control for non-specific effects of NirCVS. We found that both visual and vestibular events increased somatosensory sensitivity. Critically, we found no evidence for supra-additive multisensory enhancement when both visual and vestibular signals were administered together: in fact, we found a trend towards sub-additive interaction. The results are compatible with a vestibular role in somatosensory gain regulation

Galvanic vestibular stimulation increases novelty in free selection of manual actions

Making optimal choices in changing environments implies the ability to balance routine, exploitative patterns of behavior with novel, exploratory ones. We investigated whether galvanic vestibular stimulation (GVS) interferes with the balance between exploratory and exploitative behaviors in a free action selection task. Brief right-anodal and left-cathodal GVS or left-anodal and right-cathodal GVS were delivered at random to activate sensorimotor circuits in the left and right hemisphere, respectively. A sham stimulation condition was included. Participants endogenously generated sequences of possible actions, by freely choosing successive movements of the index or middle finger of the left or right hand. Left-anodal and right-cathodal GVS, which preferentially activates the vestibular projections in the right cerebral hemisphere, increased the novelty in action sequences, as measured by the number of runs in the sequences. In contrast, right-anodal and left-cathodal GVS decreased the number of runs. There was no evidence of GVS-induced spatial bias in action choices. Our results confirm previous reports showing a polarity-dependent effect of GVS on the balance between novel and routine responses, and thus between exploratory and exploitative behaviors