Primate ips areas involved in visual 3D shape processing

Abstract

Action-oriented representations of the environment are built in the intra-parietal sulcus (IPS) by integrating information from multiple sensory modalities. Among these modalities, vision is of prime importance since it provides most of our knowledge about the 3D structure of the world (crucial for navigation and for recognition and grasping of objects). Using fMRI techniques with awake monkey (Vanduffel et al., 2001), we studied the neural network involved in 3D shape extraction from stereo focusing on the IPS. Stimuli were random lines resembling images of unfolded paper clips (Orban et al., 1999). A set of IPS regions was more activated by stereo-defined 3D shapes compared to their 2D (flat) counterparts presented in different depth planes. On the lateral bank, AIP, LIP and pIPS were significantly more 3D than 2D shape sensitive. For LIP, 3D sensitivity was observed in the anterior part while the intermediate part preferred shapes presented in different depth planes rather than in the fixation plane. On the medial bank, posterior VIP, MIP and PIP also showed 3D shape sensitivity. Overall, this IPS network is highly similar to the network activated by 2D greyscale images and drawings of objects (Denys et al. 2004), showing a shape processing oriented toward object manipulation in the IPS. Moreover, because it was shown previously that the IPS is only weakly involved in 3D extraction from motion in monkeys (Vanduffel et al. 2002), the present results highlight the importance of stereo relative to motion in 3D shape processing in the IPS.

Footnotes

 This study is supported by grants of the Queen Elisabeth Foundation, the National Research Council of Belgium, the Flemish Regional Ministry of Education (GOA2005/18), the Interuniversity Attraction Pole (IUAP5/04) and EU project IST-FET-001917 (Neurobotics). The Laboratoire Guerbet (Roissy, France) provided the contrast agent (Sinerem®)