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Kristl Claeys, Delwin T Lindsey, Erik Schutter, Paul Hecke, Guy A Orban; The neural correlate of a higher-order feature-tracking motion system revealed by fMRI. Journal of Vision 2003;3(9):790. doi: 10.1167/3.9.790.
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We examined the human neural substrate of a higher-order feature-tracking motion system (Lu et al,1999) using fMRI block design (1.5T) and two different stimulus configurations. First, we used isoluminant horizontal red/green sinewave gratings and a luminance-modulated red/black control grating (3 width, 6 height, 4.5 eccentricity right/left side, monocularly), that moved either up or down (3.75Hz, 0.5cycle/ ) or were stationary. Relative salience in the stimulus was manipulated by varying the saturation of a greenish grating that was modulated isoluminantly in spatial antiphase with a 1.0 contrast red grating. For the low-, medium-, and high-green-saturation conditions, isoluminance was determined by motion photometry in each subject (n=6) immediately before each scanning session (6 per subject). By contrasting the salience-defined motion conditions with their stationary counterparts, we observed activations in bilateral area MT+ and in the inferior parietal lobule (IPL). The functional profile of MT+ shows contralateral activity, whereas that of IPL reveals bilateral activity which is salience-specific. In the second experiment (n=12), we used the quartet apparent motion display (Temus,1938) consisting of two alternating frames (2 and 7Hz) each with two white dots (0.5 ) arrayed on the two diagonally opposed vertices of a 2 square (4 eccentricity left/right side, binocularly). This was contrasted to a control condition in which four dots were synchronously presented (7Hz). We observed activation in bilateral MT+ and other regions belonging to the lower-order motion pathway (Sunaert et al,1999), and also in IPL. Contrary to the contralateral activity in MT+, IPL showed bilateral activity and specificity for the apparent motion condition. We conclude that there are two motion-processing systems in the human brain: an energy-driven, contralateral lower-order system including area V5/MT+, and an ‘attention'-driven, bilateral higher-order system represented in IPL.
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