To investigate the coordination between the upper lid and the eye during vertical gaze changes, the movements of the lid and the eye were measured by the electromagnetic search-coil technique in three humans and two monkeys. 2. In both man and monkey, there was a close correspondence between the metrics of the lid movement and those of the concomitant eye movement during vertical fixation, smooth pursuit, and saccades. 3. During steady fixation, the eye and lid assumed essentially equal average positions; however, in man the lid would often undergo small idiosyncratic movements of up to 5 degrees when the eye was completely stationary. 4. During sinusoidal smooth pursuit between 0.2 and 1.0 Hz, the gain and phase shift of eye and lid movements were remarkably similar. The smaller gain and larger phase lag for downward smooth pursuit eye movements was mirrored in a similar reduced gain and increased phase lag for downward lid movements. 5. The time course of vertical lid movements associated with saccades was generally a faithful replica of the time course of the concomitant saccade; the similarity was especially impressive when the details of the velocity profiles were compared. Consequently, lid movements associated with vertical eye saccades are called lid saccades. 6. On average, lid saccades start some 5 ms later than the concomitant eye saccades but reach peak velocity at about the same time as the eye saccade. Concurrent lid and eye saccades in the downward direction have similar amplitudes and velocities. Lid saccades in the upward direction are often smaller and slower than the concomitant eye saccades. The relation of peak velocity versus amplitude and of duration versus amplitude are similar for lid and eye saccades. 7. To investigate the neural signal responsible for lid saccades, isometric tension and EMG activity were recorded from the lids of the two authors. 8. The isometric tensions during upward lid saccades exceeded the tensions required to hold the lid in its final position.(ABSTRACT TRUNCATED AT 400 WORDS)
