Bernard Cohen

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1. Velocity characteristics of optokinetic nystagmus (OKN) and optokinetic after-nystagmus (OKAN) induced by constant velocity full field rotation were studied in rhesus monkeys. A technique is described for estimating the dominant time constant of slow phase velocity curves and of monotonically changing data. Time constants obtained by this technique were(More)
Vestibular and optokinetic nystagmus (OKN) of monkeys were induced by platform and visual surround rotation. Vision prolonged per-rotatory nystagmus and cancelled or reduced post-rotatory nystagmus recorded in darkness. Presumably, activity stored during OKN summed with activity arising in the semicircular canals. The limit of summation was about 120 °/s,(More)
Body, head, and eye movements were measured in five subjects during straight walking and while turning corners. The purpose was to determine how well the head and eyes followed the linear trajectory of the body in space and whether head orientation followed changes in the gravito-inertial acceleration vector (GIA). Head and body movements were measured with(More)
 Trunk and head movements were characterized over a wide range of walking speeds to determine the relationship between stride length, stepping frequency, vertical head translation, pitch rotation of the head, and pitch trunk rotation as a function of gait velocity. Subjects (26–44 years old) walked on a linear treadmill at velocities of 0.6–2.2 m/s. The(More)
1. Monkeys received optokinetic stimulation at 60 degrees/s about their yaw (animal vertical) and pitch (animal horizontal) axes, as well as about other head-centered axes in the coronal plane. The animals were upright or tilted in right-side-down positions with regard to gravity. The stimuli induced horizontal, vertical, and oblique optokinetic nystagmus(More)
The time constant of the decay of slow-phase eye velocity of postrotatory nystagmus or optokinetic after-nystagmus is reduced during exposure to a stationary visual surround (visual suppression). It is also reduced after tilting the head (tilt suppression). A "dump" mechanism in the vestibulo-ocular reflex has been proposed to rapidly discharge activity(More)
The time constant of the angular vestibulo-ocular reflex (aVOR), measured from the response to steps of rotation about a yaw axis, has frequently been estimated as a single exponential. However, the slow phase velocity envelope during per- or post-rotatory nystagmus is more accurately represented by two exponential modes. One represents activity in the(More)
Vertical head and eye coordination was studied as a function of viewing distance during locomotion. Vertical head translation and pitch movements were measured using a video motion analysis system (Optotrak 3020). Vertical eye movements were recorded using a video-based pupil tracker (Iscan). Subjects (five) walked on a linear treadmill at a speed of 1.67(More)
1. We studied the contribution of the individual semicircular canals to the generation of horizontal and torsional eye movements in cynomolgus monkeys. Eye movements were elicited by sinusoidal rotation about a vertical (gravitational) axis at 0.2 Hz with the animals tilted in various attitudes of static forward or backward pitch. The gains of the(More)
Spatial orientation of the angular vestibuloocular reflex (aVOR) was studied in rhesus monkeys after complete and partial ablation of the nodulus and ventral uvula. Horizontal, vertical, and torsional components of slow phases of nystagmus were analyzed to determine the axes of eye rotation, the time constants (Tcs) of velocity storage, and its orientation(More)