Organizer: Elisa Raffaella Ferré, Royal Holloway University of London
Abstract: The vestibular system is essential for successful interactions with the environment, providing an absolute reference for orientation and gravity. Vestibular information has been traditionally considered a cue for basic behaviours, such as balance, oculo-motor adjustments, and self-motion. However, recent studies have highlighted the fundamental role played by the vestibular system in brain functions beyond reflexes and postural adjustment. These include vestibular contributions to several aspects of cognition, including multisensory perception, spatial representation, emotion, attention and body models. This symposium brings together international experts with their own unique interests to the vestibular system. Laurence Harris will present experimental results on vestibular-somatosensory interaction highlighting its role in perceiving the timing of sensory events. Elisa Ferré will focus on how vestibular inputs integrate with other sensory signals to generate coherent estimates of perceptual vertical. Finally, Christophe Lopez will illustrate the effect of vestibular stimulations on bodily self and self-other interactions. Speakers will discuss the fundamental and hitherto largely unsuspected role of vestibular signals in almost all aspects of cognition.
S2.1 Vestibular-Somatosensory Interactions Affect The Perceived Timing Of Tactile Stimuli
Laurence R. Harris* and Stefania S. Moro, Centre for Vision Research, York University
Passive rotation has been shown to alter temporal order judgments (TOJs) for tactile stimuli delivered to the hands giving an advantage to the leading hand. Here we compare the effects of physical tilt to the left or right with the effect of pure sensory stimulation created by galvanic vestibular stimulation (GVS) (evoking illusory tilts towards the cathode side, either the left or right). During tilt to one side the effect of gravity on the otoliths is equivalent to a physical acceleration away from that side (e.g., tilt left is equivalent to accelerating rightwards). We therefore predicted a “leading hand advantage” for the hand opposite to the tilt direction. TOJ thresholds for both left-hand-first and right-hand-first touches were measured separately using interleaved adaptive staircases. The mean of these two thresholds is the point of subjective simultaneity (PSS). For both physical and illusory tilt the PSS was shifted towards the hand contralateral to the tilt – equivalent to the “leading hand” during rotation. These results are discussed in terms of attention and direct sensory components evoking the “leading hand” bias. These findings add to the emerging understanding of the pervasive role of vestibular activity in many aspects of cognitive processing.
S2.2 Vestibular and Somatic Signals for Verticality
Elisa R. Ferré*, Royal Holloway University of London
On Earth, verticality defines what is “up” and what is “down” in the gravitational field. The vestibular receptors detect the direction of gravitational acceleration: when our head moves, the otoliths shift and signal to the brain head position relative to gravity. These vestibular signals are integrated with information from vision, proprioception, and viscera to form a cognitive representation of the vertical. Here we investigated how people perceive verticality for stimuli applied to the skin. A psychophysical subjective tactile vertical task has been combined with Galvanic Vestibular Stimulation (GVS). Brief left-anodal and right-cathodal GVS, right-anodal and left-cathodal GVS, or sham stimulation were delivered at random while participants judged the orientation of lines drawn on their forehead. GVS did not bias tactile verticality estimates. Conversely, roll-tilting participants’ head induced a bias in verticality estimates toward the body neuraxis. This bias was present also for stimuli not aligned with the body midline. Distinct representations of verticality might coexist: a vestibular representation, based on the direction of gravity, adopted as reference for environmental verticality perception, and a somatic representation which is not based on any online vestibular-gravitational signal, nor on the midline. The neuraxis seems a critical reference for this latter representation.
S2.3 Reciprocal interactions between own-body cognition and vestibular information processing
Christophe Lopez*, CNRS and Aix Marseille University
I will summarize recent evidence showing the interplay between own-body cognition and vestibular information processing. First, I will present data showing that caloric vestibular stimulation applied to a group of 16 healthy participants interferes with the mental representation of their body structure and shape. The data highlight an overall predominance of the left vestibular apparatus in modulating the perceived size of body parts, irrespective of the laterality of the body parts. Second, I will present results obtained in 350 otoneurological patients suffering from dizziness showing that vestibular disorders alter several aspects of self-and body perception and cognition, including the perceived shape and size of the body, body agency (the sense of being the agent of an action), body ownership and embodiment (the sense that the self is located within the physical boundaries of the body). Finally, the influence of cognition on vestibular information processing will be shown by a recent study linking social cognition to vestibular neurophysiology. We measured how observing passive motion of human influences vestibulo-spinal excitability. Healthy participants observed videos depicting passive rotations of their own body (‘self’ videos), someone else’s body (‘other’ video) or an object of the same size (‘object’ video) in a head-mounted display. At the same time, we measured vestibulo-spinal reflexes evoked by galvanic vestibular stimulation. The data show that vestibulo-spinal excitability decreased for ‘self” and ‘other’ videos when compared to ‘object’ videos. The reduction was stronger for ‘self’ than ‘other’ videos. This indicates top-down (social) modulation of vestibular information processing and provides the first evidence that social cognition has a pre-reflective influence on vestibular processing.