Single-Trial fMRI Decoding of 3D Motion with Stereoscopic and Perspective Cues

How does the brain process 3D motion? We focused on the human motion complex (hMT+), extending insights from monkey studies. Using 3D-motion stimuli containing perspective and/or stereoscopic cues, we investigated the hierarchy within the motion complex in humans of both sexes to understand the neural mechanisms underlying motion perception. On each trial we decoded 3D motion direction (toward/away) based on the BOLD response in primary visual cortex (V1), and regions within hMT+ including the middle temporal (MT) and medial superior temporal (MST) areas, and the fundus of the superior temporal sulcus (FST). We found that 3D-motion direction could be reliably decoded from all four areas but accuracy depended on cue content. MT and FST showed greatest decoding accuracy with perspective and stereoscopic cues, respectively. Decoding of motion direction in V1 and MST could be explained by retinotopic biases in the BOLD response to motion stimuli. MT and FST were less impacted by such biases. We also identified significant behavioral differences between participants: some were proficient at using stereoscopic cues and others performed near chance. Good behavioral performance with stereoscopic cues was accompanied by better decoding performance in FST but not MT. A control experiment that eliminated 3D motion percepts for stereoscopic stimuli, but not perspective stimuli, revealed that unlike MT, decoding accuracy in FST was influenced by perceptual components of 3D motion. Our findings support that MT and FST play distinct roles in the analysis of visual motion and are key in the transformation of retinal input into perceptual report.