ABSTRACT
The ability to read depends on a region in ventral occipito-temporal cortex known as the “visual word form area” (VWFA). The VWFA, which has several sub-regions, lies amidst a collection of areas involved in visual recognition. Although it responds best to written words, its selectivity is not absolute, and it exhibits top-down modulations that are not well understood. Here, we used fMRI to investigate the interaction of bottom-up visual factors and top-down cognitive factors in the VWFA and neighboring regions. We presented participants with strings of letters and non-letter shapes at a range of visual field locations. For each stimulus type, participants performed a task in which the stimuli were task-relevant (lexical decision and gap localization, respectively), and a task in which the stimuli were irrelevant (detecting fixation dot color changes). Standard models of attention predict that all stimuli would evoke larger responses when task-relevant than irrelevant, throughout visual cortex. To the contrary, the data showed surprising patterns specific to the VWFA. Letter strings did evoke much larger responses when they were task-relevant than irrelevant, even when presented too far in the periphery to be recognized. In contrast, non-letter shapes evoked smaller responses when they were task-relevant. Connectivity analyses suggest that these task effects are due to flexible communication between the VWFA and Broca’s area. We conclude that top-down modulations in visual cortex do not merely enhance representations of attended stimuli, but can boost processing in specific brain regions, contingent on engagement in specific tasks.
SIGNIFICANCE A person’s cognitive state determines how their brain responds to visual stimuli. The most common such effect is a response enhancement when stimuli are attended rather than ignored. We report a surprising twist on such attention effects, focusing on a brain region that selectively processes written words. There, the enhancement of responses to attended stimuli only occurred for letter strings, whereas responses to visually similar shapes were suppressed when attended. This selective task effect was accompanied by correlated activity in higher-level language regions, which appear to send excitatory feedback into particular visual regions only when the observer is trying to read. That feedback enables the discrimination of real and nonsense words, and is distinct from generic effects of visual attention.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Competing Interest Statement: The authors have no competing interests to declare.
