The study initially explored the frontal eye field's (FEF) control of predictive eye movements, i.e., eye movements driven by previous rather than current sensory signals. Five monkeys were trained to pursue horizontal target motion, including sinusoidal targets and "random-walk" targets which sometimes deviated from a sine motion. Some subjects also tracked other target trajectories and optokinetic motion. FEF ablations or cold lesions impaired predictive pursuit, but also degraded visually guided foveal pursuit of all targets. Unilateral lesions impaired pursuit of targets moving in both horizontal orbital fields and in both directions of movement. Saccadic estimates of target motion were generally accurate. The slow-phase velocity of optokinetic pursuit (collected after 54 s of OKN) also appeared normal. Pursuit recovered over 1-3 weeks after surgery but the deficits were then reinstated by removal of FEF in the other hemisphere. Thereafter, a slight deficit persisted for up to 10 weeks of observation in two subjects. The pattern of symptoms suggests that FEF lies subsequent to parietal area MST and prior to the pontine nuclei in controlling pursuit eye movements.
The frontal eye field (FEF), an area in the primate frontal lobe, has long been considered important for the production of eye movements. Past studies have evoked saccade-like movements from the FEF using electrical stimulation in animals that were not allowed to move their heads. Using electrical stimulation in two monkeys that were free to move their heads, we have found that the FEF produces gaze shifts that are composed of both eye and head movements. Repeated stimulation at a site evoked gaze shifts of roughly constant amplitude. However, that gaze shift could be accomplished with varied amounts of head and eye movements, depending on their (head and eye) respective starting positions. This evidence suggests that the FEF controls visually orienting movements using both eye and head rotations rather than just shifting the eyes as previously thought.
Two rhesus monkeys viewed black/white photographic slides depicting rhesus, human, chimpanzee, and schematic faces with direct gazes. Eye-track apparatus was used to assign visual fixations to one of four facial regions: the two eyes, nose, or mouth. Results showed that the eyes of stimulus faces received a disproportionate number of fixations from both observers across all stimulus face types. Stimulus faces depicting rhesus and human facial gestures shifted scan patterns somewhat, but did not disrupt the preoccupation with eyes. When the features of schematic faces were rearranged into non-facelike configurations, fixations directed to schematic stimuli were typically reduced in number.
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