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Storing upright turns: how visual and vestibular cues interact during the encoding and recalling process.

Vidal M, Bülthoff HH - Exp Brain Res (2009)

Bottom Line: First, we found that in none of the conditions did the reproduced motion dynamics follow that of the presentation phase (Gaussian angular velocity profiles).Third, when the intersensory gain was preserved, the bimodal reproduction was more precise (reduced variance) and lay between the two unimodal reproductions.Fourth, when the intersensory gain was modified, the bimodal reproduction resulted in a substantially larger change for the body than for the visual scene rotations, which indicates that vision prevails for this rotation displacement task when a matching problem is introduced.

View Article: PubMed Central - PubMed

Affiliation: Max Planck Institute for Biological Cybernetics, Tübingen, Germany. manuel.vidal@college-de-france.fr

ABSTRACT
Many previous studies have focused on how humans combine inputs provided by different modalities for the same physical property. However, it is not yet very clear how different senses providing information about our own movements combine in order to provide a motion percept. We designed an experiment to investigate how upright turns are stored, and particularly how vestibular and visual cues interact at the different stages of the memorization process (encoding/recalling). Subjects experienced passive yaw turns stimulated in the vestibular modality (whole-body rotations) and/or in the visual modality (limited lifetime star-field rotations), with the visual scene turning 1.5 times faster when combined (unnoticed conflict). Then they were asked to actively reproduce the rotation displacement in the opposite direction, with body cues only, visual cues only, or both cues with either the same or a different gain factor. First, we found that in none of the conditions did the reproduced motion dynamics follow that of the presentation phase (Gaussian angular velocity profiles). Second, the unimodal recalling of turns was largely uninfluenced by the other sensory cue that it could be combined with during the encoding. Therefore, turns in each modality, visual, and vestibular are stored independently. Third, when the intersensory gain was preserved, the bimodal reproduction was more precise (reduced variance) and lay between the two unimodal reproductions. This suggests that with both visual and vestibular cues available, these combine in order to improve the reproduction. Fourth, when the intersensory gain was modified, the bimodal reproduction resulted in a substantially larger change for the body than for the visual scene rotations, which indicates that vision prevails for this rotation displacement task when a matching problem is introduced.

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Illustration of the different presentation and reproduction phases defining the six experimental conditions that were studied. The presentation phase was either a purely visual (V to V) or a purely vestibular (B to B) stimulation representing upright passive rotations, or a body rotation coupled with the corresponding visual rotation amplified by a gain factor of 1.5 (VB to V, VB to B, VB to VBsame and VB to VBdiff). In the reproduction phase, subjects were asked to reproduce backwards the perceived rotation in one of the four following sensory contexts: with vision only (V to V and VB to V), body only (B to B and VB to B), or both modalities with the same 1.5 gain (VB to VBsame) or with a different 1.0 gain (VB to VBdiff) than during the presentation
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Fig2: Illustration of the different presentation and reproduction phases defining the six experimental conditions that were studied. The presentation phase was either a purely visual (V to V) or a purely vestibular (B to B) stimulation representing upright passive rotations, or a body rotation coupled with the corresponding visual rotation amplified by a gain factor of 1.5 (VB to V, VB to B, VB to VBsame and VB to VBdiff). In the reproduction phase, subjects were asked to reproduce backwards the perceived rotation in one of the four following sensory contexts: with vision only (V to V and VB to V), body only (B to B and VB to B), or both modalities with the same 1.5 gain (VB to VBsame) or with a different 1.0 gain (VB to VBdiff) than during the presentation

Mentions: In the presentation phase of the first session, subjects passively experienced a whole-body upright rotation synchronized to a visual scene rotation with a gain factor of 1.5 (i.e., turning 1.5 times faster). This conflict between vision and vestibular rotations was used in order to dissociate the two modalities and to be able to infer on which sensory basis the reproduction is done. We used pilot subjects to determine a good trade-off between higher gain factors for increased dissociation and gain factors closer to 1 for unnoticed conflicts. Indeed, a sensory discrepancy remaining unnoticed allows improving the ecological validity and prevents subjects from developing unnatural specific strategies for solving the task (De Gelder and Bertelson 2003). This issue was verified for each subject in a debriefing questionnaire at the end of the experiment. After a 2-s delay started the reproduction phase. Subjects were instructed to reproduce the perceived amplitude of the rotation (i.e., rotation displacement) in the opposite direction using the joystick in one of the four following conditions (see Fig. 2): with the visual scene rotation but no platform motion (VB to V), with the body rotation and only the fixation cross displayed on the screen (VB to B), with vision and body where the vision/body rotation used the same 1.5 gain (VB to VBsame) or a different 1.0 gain (VB to VBdiff) than during the presentation phase.Fig. 2


Storing upright turns: how visual and vestibular cues interact during the encoding and recalling process.

Vidal M, Bülthoff HH - Exp Brain Res (2009)

Illustration of the different presentation and reproduction phases defining the six experimental conditions that were studied. The presentation phase was either a purely visual (V to V) or a purely vestibular (B to B) stimulation representing upright passive rotations, or a body rotation coupled with the corresponding visual rotation amplified by a gain factor of 1.5 (VB to V, VB to B, VB to VBsame and VB to VBdiff). In the reproduction phase, subjects were asked to reproduce backwards the perceived rotation in one of the four following sensory contexts: with vision only (V to V and VB to V), body only (B to B and VB to B), or both modalities with the same 1.5 gain (VB to VBsame) or with a different 1.0 gain (VB to VBdiff) than during the presentation
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2800859&req=5

Fig2: Illustration of the different presentation and reproduction phases defining the six experimental conditions that were studied. The presentation phase was either a purely visual (V to V) or a purely vestibular (B to B) stimulation representing upright passive rotations, or a body rotation coupled with the corresponding visual rotation amplified by a gain factor of 1.5 (VB to V, VB to B, VB to VBsame and VB to VBdiff). In the reproduction phase, subjects were asked to reproduce backwards the perceived rotation in one of the four following sensory contexts: with vision only (V to V and VB to V), body only (B to B and VB to B), or both modalities with the same 1.5 gain (VB to VBsame) or with a different 1.0 gain (VB to VBdiff) than during the presentation
Mentions: In the presentation phase of the first session, subjects passively experienced a whole-body upright rotation synchronized to a visual scene rotation with a gain factor of 1.5 (i.e., turning 1.5 times faster). This conflict between vision and vestibular rotations was used in order to dissociate the two modalities and to be able to infer on which sensory basis the reproduction is done. We used pilot subjects to determine a good trade-off between higher gain factors for increased dissociation and gain factors closer to 1 for unnoticed conflicts. Indeed, a sensory discrepancy remaining unnoticed allows improving the ecological validity and prevents subjects from developing unnatural specific strategies for solving the task (De Gelder and Bertelson 2003). This issue was verified for each subject in a debriefing questionnaire at the end of the experiment. After a 2-s delay started the reproduction phase. Subjects were instructed to reproduce the perceived amplitude of the rotation (i.e., rotation displacement) in the opposite direction using the joystick in one of the four following conditions (see Fig. 2): with the visual scene rotation but no platform motion (VB to V), with the body rotation and only the fixation cross displayed on the screen (VB to B), with vision and body where the vision/body rotation used the same 1.5 gain (VB to VBsame) or a different 1.0 gain (VB to VBdiff) than during the presentation phase.Fig. 2

Bottom Line: First, we found that in none of the conditions did the reproduced motion dynamics follow that of the presentation phase (Gaussian angular velocity profiles).Third, when the intersensory gain was preserved, the bimodal reproduction was more precise (reduced variance) and lay between the two unimodal reproductions.Fourth, when the intersensory gain was modified, the bimodal reproduction resulted in a substantially larger change for the body than for the visual scene rotations, which indicates that vision prevails for this rotation displacement task when a matching problem is introduced.

View Article: PubMed Central - PubMed

Affiliation: Max Planck Institute for Biological Cybernetics, Tübingen, Germany. manuel.vidal@college-de-france.fr

ABSTRACT
Many previous studies have focused on how humans combine inputs provided by different modalities for the same physical property. However, it is not yet very clear how different senses providing information about our own movements combine in order to provide a motion percept. We designed an experiment to investigate how upright turns are stored, and particularly how vestibular and visual cues interact at the different stages of the memorization process (encoding/recalling). Subjects experienced passive yaw turns stimulated in the vestibular modality (whole-body rotations) and/or in the visual modality (limited lifetime star-field rotations), with the visual scene turning 1.5 times faster when combined (unnoticed conflict). Then they were asked to actively reproduce the rotation displacement in the opposite direction, with body cues only, visual cues only, or both cues with either the same or a different gain factor. First, we found that in none of the conditions did the reproduced motion dynamics follow that of the presentation phase (Gaussian angular velocity profiles). Second, the unimodal recalling of turns was largely uninfluenced by the other sensory cue that it could be combined with during the encoding. Therefore, turns in each modality, visual, and vestibular are stored independently. Third, when the intersensory gain was preserved, the bimodal reproduction was more precise (reduced variance) and lay between the two unimodal reproductions. This suggests that with both visual and vestibular cues available, these combine in order to improve the reproduction. Fourth, when the intersensory gain was modified, the bimodal reproduction resulted in a substantially larger change for the body than for the visual scene rotations, which indicates that vision prevails for this rotation displacement task when a matching problem is introduced.

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