Simultanagnosia: when all you can see are trees, the forest still rules.

We investigated the nature of covertly processed visual elements in a patient with simultanagnosia, a disorder characterized by the inability to perceive multiple aspects of a visual scene all at once. Using the first letter of the color words red, green, or blue, we created a novel testing paradigm that combined Navon global-local stimuli with a single-letter Stroop task. The letters R, G, or B were arranged in the overall configuration of a large R, G, or B. The patient never could report seeing the larger letter, and always could name the smaller letters. But, when asked to name ink color only, and ignore letter identity, the large letter covertly affected responding. That is, when the large letter was the same as the first letter of the ink color, the patient named ink color more quickly and accurately than when the large letter was incongruent with the correct response. Moreover, when the covert global and overt local visual processing conflicted, the global letter always dominated over the local letters, despite the patient's inability to perceive it consciously. These data show that the covert processing of global visual information in simultanagnosia can dominate overt local information, even across different streams of information processing.