Fast perception of binocular disparity

Is depth perception from binocular disparities-stereopsis-slow or fast? Many of the temporal properties of stereopsis are known. For example, rapidly changing disparities are perceptually difficult to track, which suggests that stereopsis is generally slow. But, remarkably, this basic question has not yet been addressed. We compared speed-accuracy trade-off functions between 2 forced-choice discriminations: 1 based on stereoscopic depth and 1 based on luminance. Unexpectedly, both speed-accuracy trade-off functions deviated from chance levels of accuracy at the same response time-approximately 200 ms-with stereo accuracy increasing, on average, more slowly than luminance accuracy after this initial delay. Thus, the initial processing of disparity for perceived depth took no longer than the initial processing of luminance for perceived brightness. This finding, that binocular disparities are available early during visual processing, means that depth is perceived quickly, and, intriguingly, that disparities may be more important for everyday visual function than previously thought

Spatial modulation of hippocampal activity in freely moving macaques

The hippocampal formation is linked to spatial navigation, but there is little corroboration from freely moving primates with concurrent monitoring of head and gaze stances. We recorded neural activity across hippocampal regions in rhesus macaques during free foraging in an open environment while tracking their head and eye. Theta activity was intermittently present at movement onset and modulated by saccades. Many neurons were phase-locked to theta, with few showing phase precession. Most neurons encoded a mixture of spatial variables beyond place and grid tuning. Spatial representations were dominated by facing location and allocentric direction, mostly in head, rather than gaze, coordinates. Importantly, eye movements strongly modulated neural activity in all regions. These findings reveal that the macaque hippocampal formation represents three-dimensional (3D) space using a multiplexed code, with head orientation and eye movement properties being dominant during free exploration