Speech production is always accompanied by facial and gestural activity. The present study is part of a broader research project on how head movements and facial expressions are related to voice variations in different speech situations. Ten normal subjects were recorded while reading aloud, answering yes/no questions, and dialoguing with an interviewer. Rapid rising-falling eyebrow movements produced by the subjects as they spoke were associated with Fo rises in only 71% of the cases. This suggests that eyebrow movements and fundamental frequency changes are not automatically linked (i.e., they are not the result of muscular synergy), but are more a consequence of linguistic and communicational choices. Note also that 38% of the eyebrow movements were produced while the subject was not speaking. Thus, eyebrow movements may also serve as back-channel signals or play a role in turn-taking during conversation.

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The aim of the study was to analyse changes in the orientation and stabilization of the head and trunk and their recovery after complete unilateral loss of vestibular information in humans. The ability of nine Ménière's patients to orient and stabilize their heads and trunks in space was investigated during a simple dynamic task of knee-bends and compared with the performance of 10 healthy subjects. Patients' performance was recorded before unilateral vestibular neurotomy (UVN) and during the time-course of recovery (1 week, 1 month, 3 months). Experiments were performed both in eyes open (EO) and eyes closed (EC) conditions to evaluate the role of visual cues in the recovery process. Head and trunk mean angular position (orientation) and mean maximal angular rotation (stabilization) in the roll plane and the yaw plane were recorded using a video motion analysis system. The results indicate that, in the acute stage after UVN (1 week), patients exhibit marked impairments in head and trunk orientation in both visual conditions. In the EC condition, head and trunk were deviated towards the operated side in the roll plane and the yaw plane. Head and trunk stabilization in space was impaired in the roll plane and associated with increased stabilization of the head on the shoulders. Interestingly, vision caused a complete inversion of the orientation pattern, with head and trunk rotations towards the intact side in the roll plane and the yaw plane. Relative to darkness, vision also reduced head and trunk oscillations. Recovery from abnormal head orientation in the light and impaired head stability in both visual conditions was achieved within 1 month and 3 months after UVN, respectively. However, head and trunk orientation in the dark and trunk stabilization in the roll plane remained uncompensated 3 months post-lesion. These results suggest that unilateral vestibular loss leads to a postural syndrome similar to that described previously for various animal species. They confirm the necessity of vestibular inputs for properly stabilizing head and trunk during self-generated displacements in healthy subjects. They also support the notion that vestibular compensation relies on visual cues whose substitution role gradually decreases after UVN.

The aim of this study was to analyse how changes in vestibular and visual reference frames combine to modify body orientation in space, and to determine the relationship between postural, oculomotor and perceptive parameters. Changes in vestibular and visual references were investigated by comparing controls and vestibular defective patients (Ménière's patients tested before and one week after unilateral vestibular nerve section) under three visual contexts (light with and without vertical and horizontal coordinates, darkness). Unilateral vestibular loss was responsible for postural and perceptive deviations whose direction depended on the presence of visual reference frame. We suggest these changes vary according to the spatial reference frame patients are based on. Postural changes were related to perceptive modifications but not to eye cyclotorsion.

The unitary activities of slowly (15 SAI) and fast-adapting type I (12 FAI) skin mechanoreceptive afferent units innervating the anterior part of the human leg and foot were recorded by using the microneurographic method. The recordings were performed both at rest and on application of cutaneous stimuli of various intensities before and after exposure of the corresponding receptive fields to vibration (0.5 mm peak to peak, 100 pulses/s, 10 min). The results show that 11% of the units tested, which were previously silent, developed a bursting pattern of postvibratory activity, which lasted 12 min on average. This induced resting activity may account for the tingling sensations usually perceived after exposure to vibration. Furthermore, application of vibration to the cutaneous receptive fields impaired the response properties of the corresponding cutaneous fibers much more markedly in the case of the SAI than in the FAI units. More specifically, less than one-half of the FAI fibers tested showed a postvibratory depressed sensitivity to skin stroking applied at various velocities that persisted for only a few minutes, whereas the responses of all the SAI units to suprathreshold maintained skin indentations applied with increasing amplitudes decreased significantly for 20 min. These fairly durable changes in the transductive properties of the mechanoreceptive afferent units probably lead to an impairment of perceptual and sensorimotor processes and consequently may at least partly account for the alterations in sensorimotor performance that have been reported to occur in humans after exposure to vibration.