Evoking defined gaze directions in untrained awake monkeys.

Monkeys were partially surrounded by opaque screens except for some distant small holes through which they observed various stimuli or actions, or well-defined background patterns. Gaze direction was measured by an infrared cornea reflection method. Without training or reward, the animal's gaze was directed through one of the holes for 10-30% of the total time. With holes of appropriately small diameter, the gaze direction can be defined within a range of about 1 degree. Durations of individual glances through the holes, and dependencies on the nature of the displays are reported. The procedure is suited for the electrophysiological investigation of natural, especially foveal vision.