No identification of abrupt onsets that capture attention: evidence against a unified model of spatial attention.

Many studies have reported that spatial attention can be involuntarily captured by salient stimuli such as abrupt onsets. These involuntary shifts are often assumed to have the same effects on feature extraction as voluntary shifts: there are two different ways of moving the same attentional mechanism. According to this unified model of spatial attention, all shifts of attention should enhance the identification of attended objects. We directly tested this assumption using compatibility effects in a series of spatial cueing experiments. Participants searched a display and indicated whether the target number was greater or less than five. The salient precues were also numbers, allowing measurement of compatibility effects between the precue and the target. Precues that reliably predicted the target location produced compatibility effects (e.g., the precue "1" facilitated responding to the target "one"), indicating enhanced identification of the precue. Compatibility effects were also found for precues that were nonpredictive but had the target-finding feature (i.e., contingent capture). Critically, however, four separate experiments failed to find compatibility effects for salient abrupt onsets that were neither predictive nor task-relevant. This is surprising given that these same precues produced enormous cue validity effects (up to 186 ms), suggesting salience-based attention capture. Our findings argue against the unified model: salience-based attention capture recruits different attentional mechanisms than contingent capture or voluntary shifts in attention.