Reproduction of self-rotation duration
Résumé
10 The vestibular system detects the velocity of the head even in complete darkness, and thus contributes to spatial orientation. However, during vestibular estimation of linear passive self-motion distance in darkness, healthy human subjects mainly rely on time, and they replicate also stimulus duration when required to reproduce previous self-rotation. We then made the hypothesis that the perception of vestibular-sensed motion duration is embedded within encoding of motion kinetics. The ability to estimate time during passive self-motion in darkness was examined with a self-rotation reproduction paradigm. Subjects were required to replicate through self-driven transport the plateau velocity (30, 60 and 90 • /s) and duration (2, 3 and 4 s) of the previously imposed whole-body rotation (trapezoid velocity profile) in complete darkness; the rotating chair position was recorded (500 Hz) during the whole trials. The results showed that the peak velocity, but not duration, of the plateau phase of the imposed rotation was accurately reproduced. Suspecting that the velocity instruction had impaired the duration reproduction, we added a control experiment requiring subjects to reproduce two successive identical rotations separated by a momentary motion interruption (MMI). The MMI was of identical duration to the previous plateau phase. MMI duration was fidelitously reproduced whereas that of the plateau phase was hypometric (i.e. lesser reproduced duration than plateau) suggesting that subjective time is shorter during vestibular stimulation. Furthermore, the accurate reproduction of the whole motion duration, that was not required, indicates an automatic process and confirms that vestibular duration perception is embedded within motion kinetics. 25 26 The contribution of the vestibular system to orientation and 27 localization of the body in space has long been suggested, 28 and recent studies have shown that indeed, for passive angular 29 whole-body motion in darkness [3,12,13,16,21,22], the brain can 30 retrieve the traveled path amplitude from vestibular information 31 (together with somatosensory information). These estimates of 32 angular self-motion are probably computed first by time integra-33 tions (from the vestibular signal of acceleration to position) and 34 then through the more topologic (spatial and temporal) "path 35 integration" [17,18]. 36 However, in our experiments on distance estimation of lin-37 ear transport [2,11], subjects used time (they mentally counted) 38 to complement vestibular information in order to evaluate their 39 self-motion magnitude. Furthermore, when required to repro-40 * Correspondence to: LDC-EPHE, (I. Israël). duce self-rotation amplitude, subjects reproduced also motion 41 duration (and peak velocity) [10,21]. We then made the hypoth-42 esis that time was reproduced "automatically", i.e. that the 43 perception of vestibular-sensed motion duration is embedded 44 within the encoding of motion kinetics and cannot be processed 45 independently during motion. 46 Subjects were required to reproduce the plateau duration of 47 the previously imposed rotation, in complete darkness. In order 48 to examine also the effect of motion velocity on time estimate, 49 different plateau velocities were used, and the subjects had to 50 replicate both the duration and the velocity of the plateau. The 51 aim of the plateau segment (stimulus shorter than 5 s) was to 52 provide target time intervals start/end cues through the motion 53 inertial acceleration steps per se, thus without additional sensory 54 input in order to avoid the possible different sensory modality 55 influence [19] on vestibular time estimation. 56 Sixteen healthy volunteers (eight men and eight women),
Domaines
Sciences cognitives
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