Markers of preparatory visual-spatial attention in sensory cortex have been described both as lateralized, slow-wave event-related potential (ERP) components and as lateralized changes in oscillatory-electroencephalography alpha power, but the roles of these markers and their functional relationship are still unclear. Here, 3 versions of a visual-spatial cueing paradigm, differing in perceptual task difficulty and/or response instructions, were used to investigate the functional relationships between posterior oscillatory-alpha changes and our previously reported posterior, slow-wave biasing-related negativity (swBRN) ERP activity. The results indicate that the swBRN reflects spatially specific, pretarget preparatory activity sensitive to the expected perceptual difficulty of the target detection task, correlating in both location and strength with the early sensory-processing N1 ERP to the target, consistent with reflecting a preparatory baseline-shift mechanism. In contrast, contralateral event-related decreases in alpha-band power were relatively insensitive to perceptual difficulty and differed topographically from both the swBRN and target N1. Moreover, when response instructions emphasized making immediate responses to targets, compared with prescribing delayed responses, contralateral alpha-event-related desynchronization activity was particularly strong and correlated with the longer latency target-P3b activity. Thus, in contrast to the apparent perceptual-biasing role of swBRN activity, contralateral posterior alpha activity may represent an attentionally maintained task set linking stimulus-specific information and task-specific response requirements.