Superior colliculus control of the horizontal saccadic burst generator

The control of horizontal saccadic eye movements from positions other than primary position has not been well documented in the literature. This research addresses the question of how horizontal nonprimary saccades are initiated and controlled and how corrective saccades are generated with shortened latencies.; Horizontal saccades are computer simulated, using a linear homeomorphic muscle model innervated by known and hypothesized neural circuitry. These neural circuits represent neural pathways from the retina to the brain-stem areas responsible for generating the high frequency neural burst that causes the eye muscles to contract at saccade velocities. Spatial information, generated in the retina, is transformed into a temporal code to control the duration of the neural burst. This duration is monitored through a hypothesized premotor neural integrator. Final position of the eye is controlled by the firing frequency of motoneurons innervating the oculomotor muscles. This steady state firing frequency is generated by a different neural integrator from that used to control the pulse duration. Pre-integrator scaling is used to adjust the steady state firing and pulse duration for saccades starting at other than primary position.; Data are recorded in the lab, using infrared radiation reflected from the cornea-scleral interface of the subject's eye. Horizontal saccades are initiated by a display of nine LEDs, which are separated by five degrees and centered at primary position. Under computer control, seventy-two combinations of unique saccades are elicited and recorded. Calibration is achieved through a polynomial least squares fit between the detector readings and the eye position at the nine LED positions. The detector readings are sampled at one kilohertz, are stored on computer hard disk, and are then low-passed filtered. Velocity estimates are from a band-limited derivative filter.