Cortical mechanisms of visual context processing in singleton search.

When searching for a target object presented in a context of other, irrelevant objects, the dissimilarity between target and surrounding context elements as well as the similarity between context elements themselves affect search efficiency. The present functional imaging study explored the cortical mechanisms involved in processing the same target when surrounded by context arrangements of varying homogeneity. Results showed that brain activity increased in the precuneus, cingulate gyrus, and the middle temporal gyrus as context homogeneity and local feature contrast increased. Contexts with low homogeneity and local feature contrast, compared to contexts with high homogeneity and local feature contrast, increasingly involved areas near the corpus callosum and the medial frontal gyrus. The results support the assumption that contextual grouping and local target detection both contribute to perform the visual search task.