Oculomotor capture by search-irrelevant features in visual working memory: on the crucial role of target–distractor similarity

When searching for varying targets in the environment, a target template has to be maintained in visual working memory (VWM). Recently, we showed that search-irrelevant features of a VWM template bias attention in an object-based manner, so that objects sharing such features with a VWM template capture the eyes involuntarily. Here, we investigated whether target–distractor similarity modulates capture strength. Participants saccaded to a target accompanied by a distractor. A single feature (e.g., shape) defined the target in each trial indicated by a cue, and the cue also varied in one irrelevant feature (e.g., color). The distractor matched the cue’s irrelevant feature in half of the trials. Nine experiments showed that target–distractor similarity consistently influenced the degree of oculomotor capture. High target–distractor dissimilarity in the search-relevant feature reduced capture by the irrelevant feature (Experiments 1, 3, 6, 7). However, capture was reduced by high target–distractor similarity in the search-irrelevant feature (Experiments 1, 4, 5, 8). Strong oculomotor capture was observed if target–distractor similarity was reasonably low in the relevant and high in the irrelevant feature, irrespective of whether color or shape were relevant (Experiments 2 and 5). These findings argue for involuntary and object-based, top-down control by VWM templates, whereas its manifestation in oculomotor capture depends crucially on target–distractor similarity in relevant and irrelevant feature dimensions of the search object.