Fig. 1.

Experimental setup, passive fixation task, and heading discrimination task. A: schematic illustration of the virtual reality apparatus. Monkeys were seated on a motion platform, with 6 degrees of freedom, that provided the vestibular stimulus. A projector mounted on the platform displayed images of 3D optic flow, and the field coil was used to monitor eye movements. B: passive fixation task for the translation and rotation protocols. Stimuli were delivered in 26 directions corresponding to all possible combinations of azimuth and elevation sampled, in 45° increments, from a sphere. The monkey fixated the central dot for 200 ms before the translational/rotational stimulus was presented and was required to maintain fixation during the entire stimulus period of 2-s duration. C: heading discrimination task. Stimuli were delivered in 9 logarithmically spaced headings within the horizontal plane, with 0° heading corresponding to straight forward motion. After the motion stimulus was delivered, the fixation point disappeared, 2 choice targets appeared, and the monkey was required to report his perceived heading (left vs. right) by making a saccade to one of two targets.