Co‐ordination of head and eyes in the gaze changing behaviour of cats

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Abstract
Saccadic changes of gaze were studied in conscious cats implanted with electro-oculographic electrodes to register eye position and held in a device for measuring head position. When the head is free to move, almost all saccades larger than 4.degree. in amplitude are accompanied by head rotation. This head movement starts at a variable delay after the beginning of the eye movement. Most frequently, the latency is 30 ms. After finishing its saccade, the eye rotates retrogressively in the orbit to maintain a constant direction of gaze during the remaining portion of the head movement. This compensatory eye movement has an average gain of 0.96 in the absence of visual feedback. The duration and peak velocity characteristics of head-fixed saccades were measured. A typical horizontal saccade of 20.degree. in amplitude attains a peak velocity of 250.degree./s and lasts 110 ms. The duration-amplitude relationship increases by 2.1 ms/degree. Saccades aimed obliquely within the orbit possess the same duration/peak-velocity/amplitude relationships as purely horizontal saccades. The horizontal component of an oblique saccade lasts longer and has a lower peak velocity than a purely horizontal saccade of the same amplitude as this component. Relation to brain-stem control of oblique saccades is discussed. A saccade is initially programmed to achieve the desired gaze change without aid from the head. The saccade is slowed down to prevent gaze overshoot when the head moves. Since this saccadic attenuation occurs even during passive head movement, it must be due to feedback from peripheral sensors of head rotation, and probably represents the initial stage of the compensatory eye movement. Since the axes of horizontal head and eye rotation are horizontally separated, then the gain of compensatory eye movements apparently rises as the viewing distance decreases to maintain fixation during head movements. This prediction was confirmed.