The article by Posner, Snyder, and Davidson explores the relationship between attention and the detection of visual signals. They find that subjects' detection latencies are reduced when they receive a cue indicating where in the visual field the signal will occur, suggesting an alignment of the central attentional system with the pathways activated by the visual input. The authors argue against the idea that this improvement is due to a reduced criterion at the expected target position, as it ignores important constraints on how expectancy improves performance. These constraints include the active nature of expectancy, the specificity of spatial information, the possibility of improved latency without accuracy, and the limited ability to lower the criterion at non-contiguous positions. The authors propose a framework involving a limited-capacity attentional mechanism, which better captures these constraints than a general criterion-setting approach. Using this framework, they find that attention shifts are not closely related to saccadic eye movements and that the retina is equipotential with respect to attention shifts for luminance detection, regardless of whether stimuli occur in the fovea or periphery. The article also discusses the implications of these findings for the study of attention and the visual system. It suggests that attention is not closely coupled to the structure of the saccadic eye movement system and that attention cannot be allocated freely but is directed only over contiguous portions of the visual field. The authors conclude that their results support the idea of an attentional spotlight that is not tied to foveal vision and that attention cannot compensate for structural deficiencies in acuity.The article by Posner, Snyder, and Davidson explores the relationship between attention and the detection of visual signals. They find that subjects' detection latencies are reduced when they receive a cue indicating where in the visual field the signal will occur, suggesting an alignment of the central attentional system with the pathways activated by the visual input. The authors argue against the idea that this improvement is due to a reduced criterion at the expected target position, as it ignores important constraints on how expectancy improves performance. These constraints include the active nature of expectancy, the specificity of spatial information, the possibility of improved latency without accuracy, and the limited ability to lower the criterion at non-contiguous positions. The authors propose a framework involving a limited-capacity attentional mechanism, which better captures these constraints than a general criterion-setting approach. Using this framework, they find that attention shifts are not closely related to saccadic eye movements and that the retina is equipotential with respect to attention shifts for luminance detection, regardless of whether stimuli occur in the fovea or periphery. The article also discusses the implications of these findings for the study of attention and the visual system. It suggests that attention is not closely coupled to the structure of the saccadic eye movement system and that attention cannot be allocated freely but is directed only over contiguous portions of the visual field. The authors conclude that their results support the idea of an attentional spotlight that is not tied to foveal vision and that attention cannot compensate for structural deficiencies in acuity.