[Temporal characteristics of signal enhancement by visual attention]

The effects of spatial attention by precuing the location of the target stimulus are attributed to two mechanisms: noise reduction and stimulus signal enhancement. The signal enhancement hypothesis proposes that attention directly improves the quality of the stimulus representation. In this study, we examined the temporal characteristics of signal enhancement by combining an orientation discrimination sensitivity measurement and the Speed-Accuracy Trade-off procedure. To minimize the spatial uncertainty, target position was indicated in advance. We found that the valid precue improved the orientation discrimination sensitivity by speeding up the rate of information processing, while not affecting the asymptotic level of sensitivity. We conclude that the signal enhancement by the attention is observed only at the early stage of information processing, and it has different temporal characteristics from that of noise reduction.