Evidence against the signal suppression hypothesis in the capture-probe paradigm

The signal suppression hypothesis (Gaspelin et al., 2015, 2018) argues that attentional capture by a salient, singleton distractor can be preempted through top-down inhibitory mechanisms, so long as observers have foreknowledge of the singleton’s features, i.e. its color and shape. Several recent studies have supported this view using the capture-probe visual search paradigm: by interleaving a probe task in which participants report letters that appear on each search item, inferences can be drawn about relative attentional deployment to these items. Largely, this paradigm has shown that probe recall associated with a singleton distractor is reduced relative to nonsingletons, suggesting distractor suppression. But given that these nonsingletons usually have the same color as the target while singletons do not, we hypothesized that a global facilitation of the target color, rather than singleton suppression, could drive this effect. In several experiments, we show that enhancement of the baseline nonsingleton distractors explains “below baseline suppression” as well as some effects previously seen in the capture-probe paradigm. First, when nonsingletons were presented in an irrelevant color different from the target and singleton, the difference in attention between distractor types was abolished. Second, after manipulating the color of nonsingletons, we found that attention to nonsingletons was affected by their color similarity to the target, with little or no such effect on singleton distractors. Finally, we tested the claim by Gaspelin & Luck (2018) that the putative “distractor suppression” requires fixed singleton features. In contrast to their findings, we found that this effect does appear to occur when singleton features vary trial-by-trial, so long as nonsingleton features remain fixed and benefit from the target’s global feature enhancement. Rather than preattentive feature suppression, these and previous results can be parsimoniously explained by global target-feature enhancement, which affects the baseline used to measure distractor suppression.