The role of neck afferents in subjective orientation in the visual and tactile sensory modalities.

International audienceWe studied the influence of neck afferents on the perception of orientation. In Experiment 1, we investigated the effect of head tilt on the subjective vertical in both the visual and tactile modalities. The results showed that head tilt triggers an Aubert effect in the visual modality and a M?r effect in the tactile modality. Significant positive correlations between the two adjustment modalities were restricted to head tilt to the left. In Experiment 2, we investigated the role of neck afferents on tactile orientation in seated and supine positions. The results showed that, in the supine position, the tactile E-effect was twice as large as in the seated position. These experiments confirm that tactile perception of orientation is affected by neck afferents, and show that the influence of neck afferents is limited by relevant gravitational cues

Contribution of ankle, knee, and hip joints to the perception threshold for support surface rotation.

The purpose of the present experiment was to investigate the extent to which subjects can perceive, at very slow velocities, an angular rotation of the support surface about the medio-lateral axis of the ankle, knee, hip, or neck joint when visual cues are not available. Subjects were passively displaced on a slowly rotating platform at .01, .03, and .05 deg/sec. The subjects' task was to detect movements of the platform in four different postural conditions allowing body oscillations about the ankle, knee, hip, or neck joint. In Experiment 1, subjects had to detect backward and forward rotation (pitching). In Experiment 2, they had to detect left and right rotations of the platform (rolling). In Experiment 3, subjects had to detect both backward/forward and left/right rotations of the platform, with the body fixed and the head either fixed or free to move. Overall, when the body was free to oscillate about the ankle, knee, or hip joints, a similar threshold for movement perception was observed. This threshold was lower for rolling than for pitching. Interestingly, in these postural conditions, an unconscious compensation in the direction opposite to the platform rotation was observed on most trials. The threshold for movement perception was much higher when the head was the only segment free to oscillate about the neck joint. These results suggest that, in static conditions, the otoliths are poor detectors of the direction of gravity forces. They also suggest that accurate perception of body orientation is improved when proprioceptive information can be dynamically integrated