Head kinematics were studied in ten normal subjects while they executed various locomotor tasks. The movement of the body was recorded with a video system which allowed a computer reconstruction of motion of joint articulations and other selected points on the body in three dimensions. Analyses focus on head translation along the vertical axis and rotation in the sagittal plane. This was done by recording the displacement of a line approximating the plane of horizontal semi-circular canals (the Frankfort plane: F-P). Four conditions were studied: free walking (W) walking in place (WIP) running in place (R) and hopping (H). In the 4 experimental conditions, amplitude and velocity of head translation along the vertical axis ranged from 1 cm to 25 cm and 0.15 m/s to 1.8 m/s. In spite of the disparities in the tasks regarding the magnitude of dynamic components, we found a significant stabilization of the F-P around the earth horizontal. Maximum amplitude of F-P rotation did not exceed 20 degrees in the 4 situations. Vertical angular velocities increased from locomotion tasks to the dynamic equilibrium task although the maximum values remained less than 140 degrees/s. Predominant frequencies of translations and rotations in all the tasks were within the range 0.4-3.5 Hz and harmonics were present up to 6-8 Hz. During walking in darkness, mean head position is tilted downward, with the F-P always below the earth horizontal. Darkness did not significantly influence the amplitude and velocity of head angular displacement during W, WIP and R, but during H the amplitude decreased by 37%. Residual head angular displacement is found to compensate for head translation during the 4 conditions. Our study emphasizes the importance of head stabilization as part of the postural control system and described as a basis for inertial guidance.

This experiment, which extends a previous investigation (Pozzo et al. 1990), was undertaken to examine how head position is controlled during natural locomotor tasks in both normal subjects (N) and patients with bilateral vestibular deficits (V). 10 normals and 7 patients were asked to perform 4 locomotor tasks: free walking (W), walking in place (WIP), running in place (R) and hopping (H). Head and body movements were recorded with a video system which allowed a computed 3 dimensional reconstruction of selected points in the sagittal plane. In order to determine the respective contribution of visual and vestibular cues in the control of head angular position, the 2 groups of subjects were tested in the light and in darkness. In darkness, the amplitude and velocity of head rotation decreased for N subjects; these parameters increased for V subjects, especially during R and H. In darkness, compared to the light condition, the mean position of a line placed on the Frankfort plane (about 20-30 degrees below the horizontal semi-circular canal plane) was tilted downward in all conditions of movement, except during H, for N subjects. In contrast, this flexion of the head was not systematic in V subjects: the Frankfort plane could be located above or below earth horizontal. In V subjects, head rotation was not found to be compensatory for head translation and the power spectrum analysis shows that head angular displacements in the sagittal plane contain mainly low frequencies (about 0.3-0.8 Hz). The respective contribution of visual and vestibular cues in the control of the orientation and the stabilization of the head in space is discussed.

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Head kinematics was studied in 10 normal subjects (NS) and 7 patients (P) with bilateral vestibular deficit while they executed various locomotor tasks. The movement of the body was recorded with a video system which allowed a computer reconstruction of the motion ofjoint articulations and other selected points on the body in three dimensions. Analyses focus on head translation along the vertical axis and rotation in the sagittal plane. Two conditions were studied: free walking (W) and hopping (H). The subjects were tested in light and in darkness. In NS, while walking in darkness, mean head position was tilted downward. In contrast, this flexion was not systematic in P. Darkness did not significantly influence the amplitude and velocity of head angular displacement during W, but, during H the amplitude decreased by 37% for NS. During H in darkness, head stabilization decreased for P. These results suggest that head kinematics, during natural locomotor tasks, could be used to evaluate vestibular deficiencies. Acta Otolaryngol Downloaded from informahealthcare.com by McMaster University on 02/18/15 For personal use only. Acta Otolaryngol Downloaded from informahealthcare.com by McMaster University on 02/18/15 For personal use only.

In this paper we address the problem of recovering structure and motion from a large number of intrinsically calibrated perspective cameras. We describe a method that combines (1) weak-perspective reconstruction in the presence of noisy and missing data and (2) an algorithm that updates weakperspective reconstruction to perspective reconstruction by incrementally estimating the projective depths. The method also solves for the reversal ambiguity associated with affine factorization techniques. The method has been successfully applied to the problem of calibrating the external parameters (position and orientation) of several multiple-camera setups. Results obtained with synthetic and experimental data compare favourably with results obtained with nonlinear minimization such as bundle adjustment.