Abstract
Several researches have shown that an attention task at the central visual field yields deterioration of visual performance in the peripheral visual field. Detection of a target with abrupt onset, however, is not much influenced by the central attention task since an abrupt onset might elicit the passive attention. To clarify spatiotemporal effects of the visual attention we measured detection performance of a smoothly appearing target in the peripheral visual field while the observer engaged in a central task. The stimulus presented at the center consisted of double rings with four possible gaps each. In the periphery a target and distracter stimuli were presented with three stimulus onset asynchronies (SOAs), −500, 0 and 500ms. The luminance of the target was temporally modulated in a half-cosine curve. In the task condition the observer answered numbers of rings that had two gaps and the location of the target detected in the periphery. In the no-task condition the observer just answered the latter. The results show that the target detection performance was obviously worse in the task condition than in the no-task condition at the −500ms SOA. Our results indicate that detecting a smoothly appearing target needs the positive attention.