Brain areas involved in perception of motion in depth: a human fMRI study

摘要

Recently Likova and Tyler (2007) reported a brain region anterior to the human MT complex (hMT+) that is specialized for motion in depth while Rokers, Cormack and Huk (2009) reported strong involvement of hMT+ itself. To resolve these conflicting results, we developed dynamic random-dot stereograms (RDS) in which we could trace the processing phases of the depth and motion components with functional magnetic resonance imaging. In our RDS, a number of layers composed of black random-dots on frontoparallel planes were stacked in the in-depth direction against a gray background predefining the motion path. In each frame, dots in one of the layers switched from black to white and then returned to black in the successive frame during which the contrast switching took place in another layer. When switching occurred in neighboring layers toward one direction, observers perceived a plane smoothly traversing in depth (condition 1); when the switching occurred in arbitrary layers in succession, observers perceived no coherent motion (condition 2). Both conditions require a prior process of representing a plane (white random-dot layer) in depth, which is possible only after binocular combination. In condition 3 the contrast-switching dots were selected across arbitrary layers, which appeared as twinkling dots in depth (condition 3). By contrasting these conditions in block designs, we found that both hMT+ and a region anterior to hMT+ are involved in the process. First, alternation of conditions 2 and 3, in which surface representation is the only feature in comparison, evoked positive blood-oxygen-level dependent (BOLD) change that is mostly contained in hMT+ and in another visual area, putative V3A. On the other hand, alternation of conditions 1 and 2, in which perception of coherent in-depth motion is the feature of interest, evoked BOLD changes in a region anterior to hMT+ (including the anterior hMT+).