Testing the contributions of proactive target and distractor templates in visual search performance

When searching for objects with particular visual features, performance is sometimes improved by the presence of a salient colour distractor, such as a red item among green objects. Attention to such distractors is thought to be suppressed when the visual system expects their specific features (e.g., redness), but a complication with this view is that distractor expectancies are generally accompanied by anticipated target features, with their own associated attentional facilitation. We tested the role of these mechanisms by separately manipulating the colour specificity of salient distractors and of targets, and thus the ability to build up feature-specific templates for each type of search item. Experiment 1 employed singleton distractors appearing in unpredictable colours, preventing the formation of a feature-specific suppression template. Nevertheless, evidence of suppression was unchanged, suggesting that it does not require a fixed, predictable distractor. In Experiment 2, the singleton colour remained fixed while the target colour varied. Without a constant target colour, markers of singleton suppression were effectively abolished. The pattern of results suggests that observed suppression effects are largely driven by global enhancement of the expected target colour, possibly in combination with a second-order suppression mechanism that is not dependent on specific distractor features.