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Shigeaki Nishina, Jose Nanez, Mitsuo Kawato, Takeo Watanabe; Global motion is processed as the entire unit but learned locally. Journal of Vision 2009;9(8):859. doi: 10.1167/9.8.859.
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A growing body of evidence by human imaging and monkey single-unit recording studies has indicated that global motion such as radial motion (expansion and contraction) and rotation as entire units are processed in MT+ and MST, respectively. Although perceptual learning of global motion is broadly reported, it is still unclear at which stage of visual processing the learning occurs. To address the question, we examined whether perceptual learning occurs on the basis of local or global motion as a result of improvement of performance in detecting a global radial motion in a display in which expanding or contracting dots slightly outnumber oppositely moving dots. First, the results showed improvement in detection performance specifically on the trained motion direction (expansion or contraction). Then, we measured the degree of transfer of the learning effect by presenting test stimuli spatially shifted so that the region of the test stimuli partially overlapped the trained region. We found that the degree of transfer was entirely dependent on similarity of local motion directions in the test stimuli to those in the trained stimulus in the overlapping area, irrespective of whether or not a test stimulus contained the same global motion direction as the trained stimulus. These results indicate that perceptual learning of a global motion stimulus, at least in the present setting, occurs at the stage of local motion processing. Interestingly while global motion is most likely processed as an entire unit in some stage of processing, it may not be learned as an entire unit however.
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