Processing 3-dimensional structure from motion in humans and macaques

Abstract

Single unit studies in monkeys suggested that area MT/V5 might be implicated in the extraction of the 3-dimensional structure of objects based upon motion cues only (Xiao et al., 1997, see also Bradley et al. 1998). The involvement of the presumptive human homologue of macaque MT/V5 (the human MT/V5+ complex) in the processing of 3D-structure-from-motion (3D-SFM) has been confirmed using fMRI (Orban et al., 1999). In addition, the latter study showed significant 3D-SFM sensitivity in a lateral occipital region and several regions in the intraparietal sulcus. In the present study, we bridged the gap between human functional imaging and monkey electrophysiology by performing contrast-agent enhanced fMRI experiments in awake monkeys (Vanduffel et al., 2001). Therefore, 8 human subjects and three monkeys were trained to fixate in the scanner while we presented two-dimensional and three-dimensional configurations of moving random lines. The human fMRI results were in agreement with those published. In monkey, the comparison of 3D versus the 2D dynamic displays revealed bilateral MR-activation in MT/V5, FST but not MST, as well as in areas V4, and VP. Smaller 3D-SFM sensitive MR-activation was observed in the intraparietal sulcus and several foci along the STS (anterior and ventral relative to FST). These results provide additional evidence that:

1. macaque MT/V5 is involved in the extraction of three-dimensional structure-from-motion, in agreement with single unit results,

2. human MT/V5+ might consist of several areas including homologous areas to macaque areas MT/V5 and FST,

3. there is an functional asymmetry between human and monkey intraparietal areas: human IPS is more involved in the processing of 3D-SFM compared to monkey IPS. sponsored by EU-project MAPAWAMO, and GSKE