Abstract
Attention can be focused and shifted voluntary, but attention can also be captured by salient stimuli in the environment. For example, in exogenous cueing experiments typically an abrupt onset presented in the periphery will capture attention automatically. Because of this reflexive shift of attention, targets that follow immediately after the cue at the same location are more efficiently processed. Contrary to this facilitation effect, less efficient processing of the target is manifested at the cued location when time between cue offset and target onset is delayed. Here we show that stimuli that are not salient or even visible can capture attention automatically; in fact, we show that attention can be captured by stimuli that are not even consciously perceived. We employed a new paradigm to present subliminal stimuli without masking them in a manual detection time task. The observation of the classic biphasic effect of facilitation followed by inhibition of return (IOR) suggests that the subliminal cue captured attention in a purely exogenous way. Since IOR can be observed only as a result of an exogenous, stimulus-driven shift of spatial attention, it is unlikely that top-down control settings or other non-attentional effects played a role. Whereas previous research has shown that attentional effects are only found when subliminal cues are task relevant, we show that subliminal cues can cause a reflexive shift of spatial attention, resulting in attentional facilitation followed by inhibition at the cued location.
This research was funded by a grant from Human Frontier Science Program (HSFP-RGP39/2005) to Jan Theeuwes.