The role of head-centric spatial reference with a static and kinetic visual disturbance

Abstract

A static or kinetic visual disturbance affects subjects' ability to estimate the direction of the gravitational vertical. This kind of error is increased by a head roll inclination. In two experiments, we combined head orientation with a static (Experiment 1: tilted frame) versus kinetic (Experiment 2: rotating disk) visual disturbance. The results showed that with a static visual disturbance, the increase of errors in the inclined head condition was mainly the consequence of a postural head effect like an Aubert effect. On the contrary, with a kinetic visual disturbance, it appears that the disk effect increases with head inclination. However, individual errors observed with the head inclined in front of a stationary disk were systematically correlated with the errors triggered by the same head inclination in front of a rotating disk. These observations confirm that the head axis spatial reference plays an important role in orientation perception, whatever the head position and the kind of visual display.The subjective visual (SV) oftilted observers with tilted head in front of a static-or kinetic visual disturbance has been shown to deviate from the gravitational vertical more than that ofobservers with head upright. This increase is generally believed to be due to the increase ofthe weighting of the visual influence, despite the fact that head inclination should produce its own effects. The main aim of the paper was to break down and mutually compare the relative effects of head tilt and visual disturbance on the sv. Aubert and Miiller EffectsIn darkness, tilts of the head and body are well known to induce constant errors in SV that are displaced either in the direction of postural inclination (the Aubert, or A effect) or in the opposite direction (the Miiller, or E effect). Many authors (for a review, see Howard, 1986) have suggested that the E effect is characteristic of small degrees of body inclination (up to 60°), whereas the A effect is observed for greater angles (>60°) oftilt. Consequently, tilting the head alone would be expected to proThis work was supported by grants from the University Pierre Mendes France ofGrenoble (CNRS) and by the Ministere de la Defense (DRET, Contract 92/150). We are grateful to Elwyn Leek for his help with the translation and to the anonymous reviewers for their helpful comments. Correspondence should be addressed to T. Ohlmann,

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“…Using high-density 192-channel EEG it was possible to record brain activity and performance in VV judgments in an ecologically valid situation (upright body axis aligned with gravity) whereas the VV judgements. Our behavioral data also revealed that the VV was significantly deviated towards the tilted visual references in the RFT, thus confirming previous observations in healthy populations (Guerraz et al, 1998;Lopez et al, 2006;Marendaz, 1998;Witkin and Asch, 1948;Zoccolotti et al, 1992). These effects were absent in the control task.…”

“…The role of vestibular and somatosensory cues in VV judgments was confirmed in participants rotated in their frontal plane and committing VV judgments errors whose amplitude and direction depended on the amount of body tilt (Kaptein and Van Gisbergen, 2004;Mittelstaedt, 1983;Van Beuzekom and Van Gisbergen, 2000;Van Beuzekom et al, 2001;Vingerhoets et al, 2009). Finally, the importance of visual cues has been demonstrated by the large deviations of the VV evoked by optic flow rotating around the line of sight (Dichgans et al, 1972;Guerraz et al, 1998;Lopez et al, 2007) and oriented visual environments (Dyde et al, 2006). In the widely used and validated 'rod and frame test' (RFT) participants are required to judge the orientation of a mobile rod that is embedded in a tilted square frame (Witkin and Asch, 1948).…”

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Perception of Verticality After Recent Cerebral Hemispheric Stroke

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