The Visual Representation of 3D Object Orientation in Parietal Cortex

Abstract

An accurate representation of three-dimensional (3D) object orientation is essential for interacting with the environment. Where and how the brain visually encodes 3D object orientation remains unknown, but prior studies suggest the caudal intraparietal area (CIP) may be involved. Here, we develop rigorous analytical methods for quantifying 3D orientation tuning curves, and use these tools to the study the neural coding of surface orientation. Specifically, we show that single neurons in area CIP of the rhesus macaque jointly encode the slant and tilt of a planar surface, and that across the population, the distribution of preferred slant-tilts is not statistically different from uniform. This suggests that all slant-tilt combinations are equally represented in area CIP. Furthermore, some CIP neurons are found to also represent the third rotational degree of freedom that determines the orientation of the image pattern on the planar surface. Together, the present results suggest that CIP is a critical neural locus for the encoding of all three rotational degrees of freedom specifying an object's 3D spatial orientation.

Reliability-dependent contributions of visual orientation cues in parietal cortex

“…Each stimulus presentation required 1,350 ms of fixation: 300 ms of black screen, followed by 1 s of a planar stimulus and then 50 ms of black screen. Single-unit extracellular action potentials were recorded using previously described methods, and stimulus-driven firing rates were calculated from the start of the visual response to the end of the 1-s stimulus presentation (14,15).…”

“…Previous studies show that neurons in the caudal intraparietal area (CIP) of the macaque monkey jointly encode the slant and tilt of a planar object (14,15), and that some CIP neurons are sensitive to both texture and disparity cues (7,8). We conjectured that the contributions of these cues to CIP responses depend on the preferred slant; specifically, that cells preferring small slants would be less sensitive to texture cues than cells preferring large slants.…”

“…Object orientation is often described using angular variables called slant (rotation about an axis perpendicular to the line of sight) and tilt (rotation about an axis parallel to the line of sight) (14,15) (Fig. S1).…”

Photometric stereo for strong specular highlights

“…Individual neurons in our brain's caudal intraparietal area (a critical neural locus for encoding 3D information of objects) are responsible for encoding slant and tilt of surfaces [53,54].…”

“…7 Slant and tilt angular variables are important parameters for encoding 3D perceptions in our brain [53,54]. The tilt of a surface corresponds to the direction of largest variation in perceived distance while slant varies with the magnitude of the gradient according to Eq.…”