The visual representation of 3D orientation in macaque areas STPp and VPS

In the current study, we investigated the neural mechanisms underlying the representation of three-dimensional (3D) surface orientation within the posterior portion of the superior temporal polysensory area (STPp) and the visual posterior Sylvian area (VPS) in the macaque brain. Both areas are known for their integration of visual and vestibular signals, which are crucial for visual stability and spatial perception. However, it remains unclear how exactly these areas represent the orientation of 3D surfaces. To tackle this question, we used random dot stereograms (RDS) to present 3D planar stimuli defined by slant and tilt, with depth via binocular disparity. Through this method, we examined how STPp and VPS encode this information. Our results suggest that both regions encode the orientation and depth of 3D surfaces, with interactions among these parameters influencing neural responses. Additionally, we investigated how motion cues affect the perception of 3D surface orientation. STPp consistently encoded plane orientation information regardless of motion cue, whereas VPS responses showed less stability. These findings shed light on the distinct processing mechanisms for 3D spatial information in different cortical areas, offering insights into the neural basis of visual stability and spatial perception. KEY POINTS: Both STPp and VPS can encode 3D surface orientation. Slant is encoded independently from tilt and disparity in STPp and VPS areas. TDD neurons shift their depth preferences based on tilt in STPp and VPS areas. STPp maintains stable 3D orientation encoding under motion conditions, while VPS shows less stability with changes in tilt and disparity preferences.