Abstract
At any moment, the world presents far more information than the brain can process. Visual attention allows the effective selection of information relevant for high priority processing, and is often more easily focused on one object than two. Both spatial selection and object attention have important consequences for the accuracy of task performance. Such effects are historically assessed primarily for relatively “easy” lower-precision tasks, yet the role of attention can depend critically on the demand for fine, high precision judgments. High precision task performance generally depends more upon attention and attention affects performance across all contrasts with or without noisy stimuli. Low precision tasks with similar processing loads generally show effects of attention only at intermediate contrasts and may be restricted to noisy display conditions. Perceptual learning can reduce the costs of inattention. The different roles of attention and task precision are accounted for within the context of an elaborated perceptual template model of the observer showing distinct functions of attention, and providing an integrated account of performance as a function of attention, task precision, external noise and stimulus contrast. Taken together, these provide a taxonomy of the functions and mechanisms of visual attention.