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Direction Repulsion Goes Global

2003; Elsevier BV; Volume: 13; Issue: 9 Linguagem: Inglês

10.1016/s0960-9822(03)00285-9

1879-0445

Christopher P. Benton, William J. Curran,

Retinal Development and Disorders

When viewing two superimposed, translating sets of dots moving in different directions, one overestimates direction difference. This phenomenon of direction repulsion is thought to be driven by inhibitory interactions between directionally tuned motion detectors [1Marshak W. Sekuler R. Mutual repulsion between moving visual targets.Science. 1979; 205: 1399-1401Crossref PubMed Scopus (148) Google Scholar, 2Mather G. Moulden B. A simultaneous shift in apparent direction further evidence for a `distribution-shift' model of direction coding.Q. J. Exp. Psychol. 1980; 32: 325-333Crossref PubMed Scopus (90) Google Scholar]. However, there is disagreement on where this occurs—at early stages of motion processing [1Marshak W. Sekuler R. Mutual repulsion between moving visual targets.Science. 1979; 205: 1399-1401Crossref PubMed Scopus (148) Google Scholar, 3Hiris E. Blake R. Direction repulsion in motion transparency.Vis. Neurosci. 1996; 13: 187-197Crossref PubMed Scopus (80) Google Scholar], when local motions are extracted; or at the later, global motion-processing stage following "pooling" of these local measures [4Wilson H.R. Kim J. A model of motion coherence and transparency.Vis. Neurosci. 1994; 11: 1205-1220Crossref PubMed Scopus (123) Google Scholar, 5Kim J. Wilson H.R. Direction repulsion between components in motion transparency.Vision Res. 1996; 36: 1177-1187Crossref PubMed Scopus (43) Google Scholar, 6Kim J. Wilson H.R. Motion integration over space interaction of the center and surround motion.Vision Res. 1997; 37: 991-1005Crossref PubMed Scopus (46) Google Scholar]. These two stages of motion processing have been identified as occurring in area V1 and the human homolog of macaque MT/V5, respectively [7Huk A.C. Heeger D.J. Pattern-motion responses in human visual cortex.Nat. Neurosci. 2002; 5: 72-75Crossref PubMed Scopus (146) Google Scholar, 8Castelo-Branco M. Formisano E. Backes W. Zanella F. Neuenschwander S. Singer W. Goebel W. Activity patterns in human motion-sensitive areas depend on the interpretation of global motion.Proc. Natl. Acad. Sci. USA. 2002; 99: 13914-13919Crossref PubMed Scopus (94) Google Scholar]. We designed experiments in which local and global predictions of repulsion are pitted against one another. Our stimuli contained a target set of dots, moving at a uniform speed, superimposed on a "mixed-speed" distractor set. Because the perceived speed of a mixed-speed stimulus is equal to the dots' average speed [9Watamaniuk S.N.J. Duchon A. The human visual system averages speed information.Vision Res. 1992; 32: 931-941Crossref PubMed Scopus (169) Google Scholar], a global-processing account of direction repulsion predicts that repulsion magnitude induced by a mixed-speed distractor will be indistinguishable from that induced by a single-speed distractor moving at the same mean speed. This is exactly what we found. These results provide compelling evidence that global-motion interactions play a major role in driving direction repulsion.