Abstract: To investigate the mechanism of visual selective attention, the present study was designed to further examine whether the controversial "within-object effect" was space-based or object-based. First, the present study replicated the previous finding by observing that the subjects responded foster to validly cued relative to invalidly cued targets, which suggested the existence of space-based attentional component. Moreover,it was found that, perceptual organization between two context objects attenuated by changing their shape and color, the "within-object effect" was independent on the distance. The latter result provided further evidence for the existence of the object-based component of visual selective attention , and suggested that, what visual attention selects is the "perceptual object" grouped by pre-attentive perceptual organization.

Key words: : selective attention, object-based, space-based, attentional shift, perceptual organization