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Erik Runeson, Scott Murray, Geoffrey Boynton; Response modulation in visual cortex by task, stimulus, and spatial attention. Journal of Vision 2011;11(11):188. doi: 10.1167/11.11.188.
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© ARVO (1962-2015); The Authors (2016-present)
We previously demonstrated that BOLD responses in area MT+ increase when observers perform a speed discrimination task relative to a color discrimination task, regardless of whether a moving or a static stimulus is attended. This suggests that task-dependent response modulation is independent of the physical properties of an attended stimulus. In the present study, we tested this further by determining whether task-driven modulation persists even in the absence of a stimulus, and whether the effect of spatial attention depends on the task being performed. In an event-related design, participants were cued on each trial to prepare for either a speed or color discrimination task on one side of fixation. Following a brief interval, a high-, low-, or zero-density (blank) field of moving colored dots appeared in each visual quadrant. Subjects reported whether or not the two fields on the cued side differed along the cued feature dimension (speed or color). Consistent with our previous results, performing a speed discrimination task increased responses in MT+ relative to a color discrimination task when a stimulus was present. We also found that performing a color discrimination task increased stimulus-driven responses in V4 relative to a speed discrimination task. However, in the absence of a stimulus these task-driven differences disappeared completely. Additionally, the type of task being performed had no influence on the effects of spatial attention in any regions of interest. These results show that task-driven response modulation is dependent on a stimulus being present within the focus of attention, and that the effects of spatial attention are independent of what task is being performed.
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