A Low-Dimensional Model of Coordinated Eye and Head Movements

Eye and head movement data, were recorded under head fixed and head-free conditions, and compared with theoretical results obtained using a nonlinear model of eye-head coordination. The model explains slow, or pursuit movement correlated closely to target movement, and saccades, or quick phases of eye movement. Eye movement under head-fixed conditions was modeled by an externally forced Duffing equation, whilst properties of head movement are described by a second externally forced Duffing equation with lower eigen frequency. In the more natural, head-free conditions where both eye and head movements are used synergetically to pursue a visual target, the vestibulocular reflex (VOR) is represented by coefficients defining the mutual coupling between these two oscillatory systems. In the present model, the oscillator that models eye movement has an inhibitory influence on head movement; head to eye coupling coefficients are included to model the influence of the VOR mechanism. Individual eye and head movement patterns in different subjects can be adequately modeled by altering the coupling coefficients. In order to adequatcly simulate those changes introduced by microgravity conditions, the coefficients defining eye-head coordination (mutual coupling) must be changed. It may be hypothesized tlmt such changes in the neurovestibular system could introduce the instability in eye-head coordination, which is known to lead to space sickness.Whitehall Foundation (S93-24

Inverse Modelling to Obtain Head Movement Controller Signal

Experimentally obtained dynamics of time-optimal, horizontal head rotations have previously been simulated by a sixth order, nonlinear model driven by rectangular control signals. Electromyography (EMG) recordings have spects which differ in detail from the theoretical rectangular pulsed control signal. Control signals for time-optimal as well as sub-optimal horizontal head rotations were obtained by means of an inverse modelling procedures. With experimentally measured dynamical data serving as the input, this procedure inverts the model to produce the neurological control signals driving muscles and plant. The relationships between these controller signals, and EMG records should contribute to the understanding of the neurological control of movements

Biomimetic direction of arrival estimation for resolving front-back confusions in hearing aids

Sound sources at the same angle in front or behind a two-microphone array (e.g., bilateral hearing aids) produce the same time delay and two estimates for the direction of arrival: A front-back confusion. The auditory system can resolve this issue using head movements. To resolve front-back confusion for hearing-aid algorithms, head movement was measured using an inertial sensor. Successive time-delay estimates between the microphones are shifted clockwise and counterclockwise by the head movement between estimates and aggregated in two histograms. The histogram with the largest peak after multiple estimates predicted the correct hemifield for the source, eliminating the front-back confusions

Vertical movement symmetry of the withers in horses with induced forelimb and hindlimb lameness at trot

Background The main criteria for lameness assessment in horses are head movement for forelimb lameness and pelvic movement for hindlimb lameness. However, compensatory head nod in horses with primary hindlimb lameness is a well‐known phenomenon. This compensatory head nod movement can be easily misinterpreted as a sign of primary ipsilateral forelimb lameness. Therefore, discriminating compensatory asymmetries from primary directly pain‐related movement asymmetries is a prerequisite for successful lameness assessment. Objectives To investigate the association between head, withers and pelvis movement asymmetry in horses with induced forelimb and hindlimb lameness. Study design Experimental study. Methods In 10 clinically sound Warmblood riding horses forelimb and hindlimb lameness were induced using a sole pressure model. The horses were then trotted on a treadmill. 3D optical motion capture was used to collect kinematic data from reflective markers attached to the poll, withers and tubera sacrale. The magnitude and side (left or right) of the following symmetry parameters, vertical difference in minimum position, maximum position and range‐up, were calculated for head, withers and pelvis. Mixed models were used to analyse data from induced forelimb and hindlimb lameness. Results For each mm increase in pelvic asymmetry in response to hindlimb lameness induction, withers movement asymmetry increased by 0.35‐0.55 mm; but towards the contralateral side. In induced forelimb lameness, for each mm increase in head movement asymmetry, withers movement asymmetry increased by 0.05‐0.10 mm, in agreement with the head movement asymmetry direction, both indicating lameness in the induced forelimb. Main limitations Results must be confirmed in clinically lame horses trotting overground. Conclusions The vertical asymmetry pattern of the withers discriminated a head nod associated with true forelimb lameness from the compensatory head movement asymmetry caused by primary hindlimb lameness. Measuring movement symmetry of the withers may thus aid in determining primary lameness location

Effects of External Loads on Human Head Movement Control Systems

The central and reflexive control strategies underlying movements were elucidated by studying the effects of external loads on human head movement control systems. Some experimental results are presented on dynamic changes weigh the addition of aviation helmet (SPH4) and lead weights (6 kg). Intended time-optimal movements, their dynamics and electromyographic activity of neck muscles in normal movements, and also in movements made with external weights applied to the head were measured. It was observed that, when the external loads were added, the subject went through complex adapting processes and the head movement trajectory and its derivatives reached steady conditions only after transient adapting period. The steady adapted state was reached after 15 to 20 seconds (i.e., 5 to 6 movements)

Motion sickness produced by head movement as a function of rotational velocity

Motion sickness produced by head movement as function of rotational velocit

Approaches to head movement

Heads can be spelled out higher than their merge-in position. The operation that the transformationalist generative literature uses to model this is called head movement. Government and Binding posited that the operation in question involves adjunction of a lower head to a higher head in narrow syntax. It has been noted early on, however, that this approach is highly problematic because head-adjunction violates several well-motivated constraints on syntactic structures. This overview article surveys the problems raised by the adjunction approach as well as the recent alternative analyses that were suggested in its stead in the Minimalist program. It evaluates the strengths and weaknesses of the alternatives, discusses to what extent they are able to eliminate the problems raised by the adjunction analysis, and also points out the new problems that they give rise to

Approaches to head movement

Heads can be spelled out higher than their merge-in position. The operation that the transformationalist generative literature uses to model this is called head movement. Government and Binding posited that the operation in question involves adjunction of a lower head to a higher head in narrow syntax. It has been noted early on, however, that this approach is highly problematic because head-adjunction violates several well-motivated constraints on syntactic structures. This overview article surveys the problems raised by the adjunction approach as well as the recent alternative analyses that were suggested in its stead in the Minimalist program. It evaluates the strengths and weaknesses of the alternatives, discusses to what extent they are able to eliminate the problems raised by the adjunction analysis, and also points out the new problems that they give rise to