Examined the flanker compatibility effect (FCE) that occurs when Ss must respond to a relevant center letter and ignore irrelevant flanking letters. The flankers processed semantically at least to some extent, and this effect decreases as the separation between target and flankers increases. In 10 experiments with a total of 438 undergraduates, visual angle was the only task feature that had a strong influence on the size of the FCE. The invariance of the FCE across conditions suggests that the mechanism for early selection rarely completely excludes unattended stimuli from semantic analysis. In addition, selective mechanisms are relatively insensitive to several factors that might be expected to influence them, supporting the view that spatial separation has a special status for visual selective attention.