What evidence shows distractors are suppressed proactively rather than captured and then rejected?

Two stories that look the same from the outside

When a bright or oddly colored object sits among plain ones, your search may go smoothly. That smoothness alone doesn't tell you why. One story is reactive: the salient object grabs your attention, you notice it's irrelevant, and you disengage—costing a moment but leaving little trace. The other is proactive: before attention can land, a top-down filter dampens the object's signal so it never wins the competition. Both stories predict decent performance, so the question is what happens in the milliseconds before you respond.

The experiments that separate them rely on two kinds of measurement. One is a probe technique: on some trials, letters appear inside the colored items, and people report what they saw. If a distractor location is suppressed, letters there are recalled worse than letters at ordinary locations—a behavioral fingerprint of suppression [4]. The other is electrical: scalp recordings pick up a negative wave (the N2pc) when attention is allocated to a location, and a positive wave (the PD) thought to index suppression. Capture-then-reject would predict the attention wave first; proactive suppression predicts the suppression wave without it [2].

The suppression signal appears without the capture signal

In one set of experiments, highly salient color singletons were placed in displays of 10 or 30 items—much larger than the 4- or 6-item displays used in earlier work, which critics said made the distractors too weak to capture attention at all. Across three experiments there was no evidence that these strong singletons captured attention; instead they were suppressed [1]. The same group then measured brain activity directly: the N2pc marker of attentional allocation was absent, while the PD suppression marker was present, even though a computational model confirmed the singleton was highly salient [2]. That combination is the crux of the argument—if attention had been captured and then rejected, the capture marker should have come first.

The probe method points the same way. When people searched for a yellow target circle among nine background circles that included a uniquely colored distractor, probe letters at the distractor's color location were recalled less accurately than at neutral locations—poorer recall where the distractor was, as expected if that spot had been dampened [4]. Because the probe measures the state of a location rather than a later corrective act, a deficit there fits suppression operating ahead of selection.

It isn't limited to one bright color—or to easy conditions

Suppression also shows up for emotional distractors. Using eye-tracking and related designs, one study reported suppression of salient-but-irrelevant emotional inputs occurring without prior attentional capture, which the authors treat as direct evidence for a proactive rather than a capture-and-reject account [3]. The abstract available here is fragmentary, so the precise measures are less clear than in the color-singleton work, but the direction of the claim is explicit.

Proactive suppression also appears to survive being busy. Participants watched a rapid stream of digits for a target, then got a search display either 2 or 8 items later. Probe recall was worse at distractor-colored locations than neutral ones at both delays—including the short lag, when attentional resources were still tied up with the digit task. The authors argue that reactive suppression likely needs attentional resources, whereas this proactive, implicit form does not [4]. And suppression is not restricted to a single item: when displays held two uniquely colored distractors of different salience, search improved as distractors were added, and a PD suppression marker appeared for the less salient distractor too when displays were mixed—evidence that multiple salient signals can be inhibited at once [5]. In one condition, though, only the more salient of two simultaneously presented distractors triggered the PD, which the authors describe as single-item suppression, so the multi-item capacity is adaptive rather than unlimited [5].

Why a pre-emptive filter is a different kind of mind

The practical upshot is that filtering distraction is not only about recovering from mistakes. If salient objects are dampened before they win the competition for attention, then a well-prepared searcher never pays the cost of disengaging in the first place—which fits the finding that suppression can be engaged while another task occupies attention [4]. It also reframes what a "distracting" object is: salience still generates a bottom-up signal, but top-down control can act on that signal early, which is how the signal suppression account describes it [1][2].

Some details remain unsettled. The evidence for emotional distractors rests on a partial abstract [3], and the multi-distractor results show that whether a second distractor is suppressed depends on how displays are arranged across trials [5]. The probe technique itself can be blunted: the researchers found that suppression effects can be hidden by floor effects in overall probe performance, which is why they introduced a method limiting how many items are probed at once [1]. Those caveats qualify how confidently the effect can be measured—they don't reverse the pattern of suppression without capture.

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