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Biomedical subjects

Jacques Droulez

Publications and source records attributed to Jacques Droulez.

7 recordsLinked to original sources
PubMed2006

Bayesian processing of vestibular information.

Complex self-motion stimulations in the dark can be powerfully disorienting and can create illusory motion percepts. In the absence of visual cues, the brain has to use angular and linear acceleration information provided by the vestibular canals and the otoliths, respectively. However, these sensors are inaccurate and ambiguous. We propose that the brain processes these signals in a statistically optimal fashion, reproducing the rules of Bayesian inference. We also suggest that this processing is related to the statistics of natural head movements. This would create a perceptual bias in favour of low velocity and acceleration. We have constructed a Bayesian model of self-motion perception based on these assumptions. Using this model, we have simulated perceptual responses to centrifugation and off-vertical axis rotation and obtained close agreement with experimental findings. This demonstrates how Bayesian inference allows to make a quantitative link between sensor noise and ambiguities, statistics of head movement, and the perception of self-motion.

Acceleration↗
PubMed2005

Postural stability in primary open angle glaucoma.

BACKGROUND: This study evaluated the visual contribution to postural steadiness in primary open angle glaucoma (POAG), in correlation with the mean deviation (MD) measured through conventional perimetry, and with the Advanced Glaucoma Intervention Study (AGIS) score, which quantifies the extent of losses in the visual field. METHODS: In 35 POAG patients and 21 age-matched normal subjects, the sway of the centre of pressure of the feet, on a firm or foam support, was recorded. The subjects stood on a force-plate with eyes closed, or with one or two eyes open. RESULTS: For all subjects, the sway velocity was lower with vision than without vision, indicating the existence of a visual contribution to posture at all stages of glaucoma. This contribution was significantly lower for POAG patients than for normals in monocular and binocular vision, and decreased with the MD, or as the AGIS score increased. Among the maximum, minimum and average values of the two monocular MD, the MD of the worse eye presented the most significant negative correlation with the visual contribution to posture. The somatosensory contribution to postural steadiness was larger in POAG patients, as compared to normals, in monocular or binocular vision. CONCLUSION: Primary open angle glaucoma induces a deficit in the visual contribution to postural steadiness, which should be taken into account for the prevention of falls.

Adult↗
PubMed2003

Perception of plane orientation from self-generated and passively observed optic flow.

We investigated the perception of three-dimensional plane orientation--focusing on the perception of tilt--from optic flow generated by the observer's active movement around a simulated stationary object, and compared the performance to that of an immobile observer receiving a replay of the same optic flow. We found that perception of plane orientation is more precise in the active than in the immobile case. In particular, in the case of the immobile observer, the presence of shear in optic flow drastically diminishes the precision of tilt perception, whereas in the active observer, this decrease in performance is greatly reduced. The difference between active and immobile observers appears to be due to random rather than systematic errors. Furthermore, perceived slant is better correlated with simulated slant in the active observer. We conclude with a discussion of various theoretical explanations for our results.

Adult↗
PubMed2002

Visuovestibular perception of self-motion modeled as a dynamic optimization process.

This article describes a computational model for the sensory perception of self-motion, considered as a compromise between sensory information and physical coherence constraints. This compromise is realized by a dynamic optimization process minimizing a set of cost functions. Measure constraints are expressed as quadratic errors between motion estimates and corresponding sensory signals, using internal models of sensor transfer functions. Coherence constraints are expressed as quadratic errors between motion estimates, and their prediction is based on internal models of the physical laws governing the corresponding physical stimuli. This general scheme leads to a straightforward representation of fundamental sensory interactions (fusion of visual and canal rotational inputs, identification of the gravity component from the otolithic input, otolithic contribution to the perception of rotations, and influence of vection on the subjective vertical). The model is tuned and assessed using a range of well-known psychophysical results, including off-vertical axis rotations and centrifuge experiments. The ability of the model to predict and help analyze new situations is illustrated by a study of the vestibular contributions to self-motion perception during automobile driving and during acceleration cueing in driving simulators. The extendable structure of the model allows for further developments and applications, by using other cost functions representing additional sensory interactions.

Acceleration↗
PubMed2002

Visual perception of planar orientation: dominance of static depth cues over motion cues.

We measured the ability to report the tilt (direction of maximal slope) of a plane under monocular viewing conditions, from static depth cues (square grid patterns) and motion parallax (small rotations of the plane about a frontoparallel axis). These two cues were presented separately, or simultaneously. In the latter case they specified tilts that were either collinear (coherent case) or orthogonal (conflict case). The field of view was small (8 degrees) or large (60 degrees). In small field, for motion parallax, the reported tilt depends strongly on the orientation of the plane relative to the rotation axis, being totally ambiguous when tilt is collinear with the rotation axis. In contrast, in large field, the reported tilt depends little on this variable, and is accurately specified by motion cues. In both cases static cues strongly dominated the tilt reports. Hence static grid patterns constitute robust tilt cues, which can dominate contradictory tilt indications from motion parallax, and should be considered as essential for the visual orientation during locomotion, or the immersion in virtual reality environments.

Adult↗
PubMed2002

Absolute distance perception during in-depth head movement: calibrating optic flow with extra-retinal information.

We investigated the ability of monocular human observer to scale absolute distance during sagittal head motion in the presence of pure optic flow information. Subjects were presented at eye-level computer-generated spheres (covered with randomly distributed dots) placed at several distances. We compared the condition of self-motion (SM) versus object-motion (OM) using equivalent optic flow field. When the amplitude of head movement was relatively constant, subjects estimated absolute distance rather accurately in both the SM and OM conditions. However, when the amplitude changed on a trial-to-trial basis, subjects' performance deteriorated only in the OM condition. We found that distance judgment in OM condition correlated strongly with optic flow divergence, and that non-visual cues served as important factors for scaling distances in SM condition. Absolute distance also seemed to be better scaled with sagittal head movement when compared with lateral head translation.

Adolescent↗