mpi-cybermotion-simulator-implementation-novel-motion-simulator-to

MPI CyberMotion Simulator: Implementation of a Novel Motion Simulator to Investigate Multisensory Path Integration in Three Dimensions

Path integration is a process in which self-motion is integrated over time to obtain an estimate of one's current position relative to a starting point 1. ...

Max Planck Institute for Biological Cybernetics

In order to test whether the control of eye movement in response to head movement requires an internal model of head orientation or instead can rely on directly sensing information about head orientation and movement, perceived gravity was separated from physical gravity to see which dominated the eye-movement response. Internal model theory suggests that the oculomotor response should be driven by perceived, internalized gravity, whereas the direct sensing theory predicts it should always be driven by vestibularly sensed gravity. Subjects lay on an airbed either supine or on their side and were sinusoidally translated along their dorsoventral body axis. The direction of perceived gravity was separated from physical gravity by performing the experiments in a room built on its side with the direction of its "floor" orthogonal to both physical gravity and the subject's translation. The swinging sum of the imposed sinusoidal acceleration with physical gravity was thus in a plane orthogonal to its sum with perceived gravity. Oculomotor responses to these swinging vectors were looked for and responses were found only to the sum of the acceleration with physical gravity, not perceived gravity. It was concluded that an internal model is not used to drive these compensatory eye movements.

Is an internal model of head orientation necessary for oculomotor control?

Do physical tilt and tilt of the visual environment affect perception of allocentric and egocentric space? We addressed this question using two perceptual-motor tasks: alignment of a tactile rod (ROD) and saccadic eye movements (EM). Nine participants indicated the vertical axis of their heads (egocentric task), as well as the direction of gravity (allocentric task). Head orientation (+/-60 degrees and 0 degrees) and visual environment orientation (+/-120 degrees, +/-60 degrees and 0 degrees) were independently manipulated in the fronto-planar roll plane. ROD and EM estimates of both allocentric and egocentric reference directions varied with head and room orientation. Physical tilt dominated allocentric estimates in the dark where overestimates of physical tilt were noted up to 11 degrees using both measures. Allocentric ROD and EM estimates were significantly correlated across all head orientations (r=.70, p<.01) but only when upright for egocentric estimates (r=.38, p<.01). The relative contributions of the visual environment, gravity's direction and long-body axis to the estimation of allocentric and egocentric directions were determined by vector modeling. This modeling found that vision determined about 14% of the allocentric ROD and EM estimates, that the long-axis body reference played no discernible role, and that the largest factor was gravity, the effective direction of which was non-veridical. For egocentric estimates, vision contributed about 3% with the largest factor being the body reference. We conclude that perception of allocentric and egocentric space is likely influenced by multiple senses that define common egocentric and allocentric frames of reference accessible for saccadic and tactile estimates of perceived self-orientation.

Perceived self-orientation in allocentric and egocentric space: effects of visual and physical tilt on saccadic and tactile measures.

Different senses have different processing times. Here we measured the perceived timing of galvanic vestibular stimulation (GVS) relative to tactile, visual and auditory stimuli. Simple reaction times for perceived head movement (438 +/- 49 ms) were significantly longer than to touches (245 +/- 14 ms), lights (220 +/- 13 ms), or sounds (197 +/- 13 ms). Temporal order and simultaneity judgments both indicated that GVS had to occur about 160 ms before other stimuli to be perceived as simultaneous with them. This lead was significantly less than the relative timing predicted by reaction time differences compatible with an incomplete tendency to compensate for differences in processing times.

Perceived timing of vestibular stimulation relative to touch, light and sound.

The brain can know about an active head movement even in advance of its execution by means of an efference copy signal. In fact, sensory correlates of active movements appear to be suppressed. Passive disturbances of the head, however, can be detected only by sensory feedback. Might the perceived timing of an active head movement be speeded relative to the perception of a passive movement due to the efferent copy (anticipation hypothesis) or delayed because of sensory suppression (suppression hypothesis)? We compared the perceived timing of active and passive head movement using other sensory events as temporal reference points. Participants made unspeeded temporal order and synchronicity judgments comparing the perceived onset of active and passive head movement with the onset of tactile, auditory and visual stimuli. The comparison stimuli had to be delayed by about 45 ms to appear coincident with passive head movement or by about 80 ms to appear aligned with an active head movement. The slow perceptual reaction to vestibular activation is compatible with our earlier study using galvanic stimulation (Barnett-Cowan and Harris 2009). The unexpected additional delay in processing the timing of an active head movement is compatible with the suppression hypothesis and is discussed in relation to suppression of vestibular signals during self-generated head movement.

Article	Year
Is an internal model of head orientation necessary for oculomotor control? Annals of the New York Academy of Sciences\| PubMed ID: 15826985	2005
Perceived self-orientation in allocentric and egocentric space: effects of visual and physical tilt on saccadic and tactile measures. Brain research\| PubMed ID: 18706895	2008
Perceived timing of vestibular stimulation relative to touch, light and sound. Experimental brain research. Experimentelle Hirnforschung. ExpÃ©rimentation cÃ©rÃ©brale\| PubMed ID: 19352639	2009
Experimental brain research. Experimentelle Hirnforschung. ExpÃ©rimentation cÃ©rÃ©brale\| PubMed ID: 20574689	2010
Perception\| PubMed ID: 21425708	2010
PloS one\| PubMed ID: 21556363	2011
Temporal processing of active and passive head movement. Experimental brain research. Experimentelle Hirnforschung. ExpÃ©rimentation cÃ©rÃ©brale\| PubMed ID: 21805199	2011

Michael Barnett-Cowan

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