The Processing of First- and Second-Order Motion in Human Visual Cortex Assessed by Functional Magnetic Resonance Imaging (fMRI)

TLDR

Using fMRI, the authors presented first‑order luminance‑defined motion and three types of second‑order motion to human subjects while recording activity in V5 (MT) and retinotopically defined V1, V2, V3, VP, V3A, and a novel V3B area. They found that V5 was strongly and motion‑specifically activated by both motion types, V1 and V2 responded to all stimuli but mainly reflected local structure, V3 and VP showed greater motion specificity and stronger responses to second‑order motion, while V3A and V3B exhibited a weaker but similar trend, supporting a model in which first‑order motion is processed in V1, second‑order motion first appears in V3/VP, and V5 (and possibly V3A/V3B) integrates both signals.

Abstract

We have examined the activity levels produced in various areas of the human occipital cortex in response to various motion stimuli using functional magnetic resonance imaging (fMRI) methods. In addition to standard luminance-defined (first-order) motion, three types of second-order motion were used. The areas examined were the motion area V5 (MT) and the following areas that were delineated using retinotopic mapping procedures: V1, V2, V3, VP, V3A, and a new area that we refer to as V3B. Area V5 is strongly activated by second-order as well as by first-order motion. This activation is highly motion-specific. Areas V1 and V2 give good responses to all motion stimuli, but the activity seems to be related primarily to the local spatial and temporal structure in the image rather than to motion processing. Area V3 and its ventral counterpart VP also respond well to all our stimuli and show a slightly greater degree of motion specificity than do V1 and V2. Unlike V1 and V2, the response in V3 and VP is significantly greater for second-order motion than for first-order motion. This trend is evident, but less marked, in V3A and V3B and absent in V5. The results are consistent with the hypothesis that first-order motion sensitivity arises in V1, that second-order motion is first represented explicitly in V3 and VP, and that V5 (and perhaps also V3A and V3B) is involved in further processing of motion information, including the integration of motion signals of the two types.