Abstract
Visual cortex is capable of processing a wide variety of stimuli for any number of behavioral tasks. So how does the specific information required for a given task get selected and routed to other necessary brain regions? In general, stimuli that are relevant to the current task evoke stronger responses than stimuli that are irrelevant, due to attentional selection on the basis of visual field location or non-spatial features. We will first review evidence that such attentional effects happen in category-selective regions, such as the visual word form area, as well as early retinotopic regions. We will then demonstrate evidence for top-down effects that are not domain-general, but extremely specific to task demands, stimulus features, and brain region. We measured fMRI responses to written words and non-letter shapes in retinotopic areas as well as word- and face-selective regions of ventral occipitotemporal cortex. In word-selective regions, letter strings evoked much larger responses when they were task-relevant (during a lexical decision task) than when they were irrelevant (during a color change task on the fixation mark). However, non-letter shapes evoked smaller responses when they were task-relevant than when irrelevant. This surprising modulation pattern was specific to word-selective regions, where response variability was also highly correlated with a region in the pre-central sulcus that is involved in spoken language. Therefore, we suggest that top-down modulations in visual cortex do not just generally enhance task-relevant stimuli and filter irrelevant stimuli, but can reflect targeted communication with broader networks recruited for specific tasks.