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Stephen V. Shepherd, Daniel Schmitt, Michael L. Platt; Visual orienting strategies in freely-moving primates. Journal of Vision 2004;4(8):658. doi: 10.1167/4.8.658.
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Visual orienting reflects the integration of sensory, motor, and motivational variables with behavioral goals. Little is known about the strategies governing visual orienting by animals in natural conditions, in part because accurate gaze-tracking technology has not been employed in field studies. We implemented a telemetric gaze-tracking system (ISCAN) to record overt visual orienting in primates moving freely in naturalistic environments. The system consists of two miniature cameras mounted on a custom-fitted thermoplastic cap. One camera monitors eye position by pupil absorption of an infrared LED reflected via dichroic mirror. A second camera records, in color, the 80 H × 40 V scene visible from the head. Video data is broadcast up to 300m by a 900MHz transmitter with a one-hour power supply, both carried in a backpack. These data are digitally combined to calculate the point of regard with maximum spatiotemporal precision of 0.156 H × 0.313 V × 16.7ms. Total system weight is approximately 670 g. System accuracy compared favorably with the scleral search coil technique when both methods were used simultaneously to measure eye movements in well-trained head-fixed rhesus macaques (Macaca mulatta). We have also habituated a prosimian primate (Lemur catta) to this equipment; measured pupil position and size during hand restraint and free movement; and recorded telemetric data even during periods of vigorous movement. These experiments provide the first measurement of visual orienting in a freely-moving animal, as well as the first quantitative measurements of eye movements in Lemur catta. The subject frequently fixated pathways, primates, and potential payoffs, and the relative priorities of these targets were strongly modulated by context. Our data suggest that nonhuman primates, like humans, deploy visual attention in a strategic goal-dependent manner.
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