When a global moving pattern is superimposed on high-contrast stationary or slowly moving stimuli, the stimuli can be perceived as disappearing and reappearing alternately for periods of several sec- onds.This visual illusory phenomenon was named“motion-induced blindness”(MIB)in recent litera- ture.So far there is no consensus on the mechanism of MIB,especially on the role of attention in this phenomenon.To examine the effect of spatial attention on MIB,the present study manipulated the participants’spatial attention by asking them to respond to two targets simultaneously presented in bilateral visual fields(the divided-attention condition)or only respond to one of them(the fo- cused-attention condition).A central arrow was presented as an endogenous cue to index the target visual field in the focused-attention condition,while a point was presented instead in the di- vided-attention condition.The results show that the percentage of accumulated invisibility period was larger for the targets in the focused-attention condition than for those in the divided-attention condition. This effect of attention is significant in upper visual field(UVF)and left lower visual field(left LVF);that is,this effect shows a hemispheric asymmetry in LVF but not in UVF.Furthermore,the percentage of accumulated invisibility period was larger for targets in left LVF than for those in right LVF in the fo- cused-attention condition,but no hemispheric asymmetry was found in the divided-attention condition. In addition,the increased percentage of accumulated invisibility period in the focused-attention condi- tion originated merely in the enhancement of the mean phase duration of disappearance in LVF,while the disappearance occurred more frequently and lasted longer for each occurrence,which led to an increase in the total invisibility period,in the focused-than divided-attention condition in UVF.These results suggest that the modulation of spatial attention on MIB has different patterns in UVF and LVF.
