Abstract
Regions of ventral occipito-temporal cortex (VOTC) prefer certain categories of stimuli at certain locations in the visual field. Activity in VOTC also depends on task demands and the distribution of attention. The visual word form area (VWFA) is one such region, being selective for letter strings near the fovea. In this study we ask whether those three variables – (1) visual field location, (2) stimulus type, and (3) task demands – independently modulate activity in the VWFA. For example, changing the task may simply scale the response all locations by a constant factor, independent of stimulus characteristics. To test that hypothesis, we manipulated all three variables in two fMRI experiments. Participants fixated a dot while letter strings or size-matched shapes flashed at varying eccentricities along the horizontal meridian. Participants were required to either perform a judgment on the stimuli or the fixation dot. In each condition, we quantified the VWFA’s “field of view” (FOV) as the portion of visual space in which stimuli evoke a strong fMRI response. Responses in the left hemisphere VWFA revealed complex interactions between stimulus characteristics, position, and task demands. For letter strings, performing a task on the stimuli amplified responses and widened the FOV, but this did not occur for non-letter shapes. Moreover, the FOV depended on font size, being wider when the letters were legible in the parafovea. These patterns did not occur in regions selective for other visual categories, nor in retinotopic visual cortex. In summary, activity in the VWFA reflects an interaction of top-down and bottom-up factors. The VWFA receives top-down enhancement to widen its field of view, but that is not merely related to allocating spatial attention. Rather, the top-down enhancement appears to be specifically engaged when the stimuli are words and the subject performs a reading-related task.