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Taiyong Bi, Zili Liu, Fang Fang; Flat BOLD-o-metric functions in motion direction discrimination in human visual cortex. Journal of Vision 2012;12(9):374. doi: 10.1167/12.9.374.
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It is commonly assumed that BOLD responses in the visual cortex are modulated by task difficulty. Here we directly tested this assumption using two fMRI experimental designs: event-related and blocked. In each trial, a static fixation cross † was first presented for 600 ms, with its longer arm serving as the directional reference that is randomly selected between 0° and 360°. Then a random-dot kinematogram (coherence: 100%, number of dots: 400, speed: 10°/sec, stimulus diameter: 8°) was presented for 200 ms. Subjects indicated whether this motion direction was clockwise or counter-clockwise with respect to the reference. The directional difference was either 3° or 9° or 15°. In the rapid event-related design, the order of trials was randomized and counterbalanced with M-sequences. In the blocked design, stimulus blocks (18 sec) were interleaved with blank blocks (12 sec). Each stimulus block consisted of six trials, all of which shared the same directional difference in absolute value. Fourteen subjects participated in this within-subjects study, with counterbalance. Behaviorally, the three directional differences gave rise to, as expected, different accuracies: 62%, 78%, and 88%. BOLD signals were analyzed in V1, V2, V3, V5/MT+, and intra-parietal sulci (posterior and anterior), all of which were sensitive to visual motion. No modulation of BOLD was found in any of these areas. We conclude that BOLD signals in the human visual cortex are not a function of task difficulty or behavioral response accuracy.
Meeting abstract presented at VSS 2012
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