The influence of feature-based statistical regularity of singletons on the attentional suppression effect

Statistical regularity refers to the regular presentation of stimuli implicit in a task. Previous studies have shown that statistical regularity based on location can affect the judgement of subsequent stimuli presented at that location. The effect of attentional capture would decrease when the distractor frequently appears in a certain location. However, comprehensive studies on whether statistical regularity based on features can modulate attention are lacking. The current study adopted a variant of the additional singleton paradigm to investigate the influence of feature-based statistical regularity of singletons on the attentional suppression effect. Experiment 1 was a single-factor within-subject design, and the presentation of a colour singleton was manipulated (colour singleton absent vs. colour singleton present) to investigate the attentional suppression effect. During the task, the participants adopted a feature search strategy to search for a target of a specific shape (diamond or circle) and ignored the salient colour singleton. In half of the trials, all stimuli were the same colour (green or red); in the other half of the trials, one colour singleton was presented among the search sequences. Similar to Experiment 1, Experiment 2 was a single-factor within-subject design, but the statistical regularity of the singleton features was manipulated (colour singleton absent vs. low probability colour singleton present vs. high probability colour singleton present). In one-third of the trials, all stimuli were the same colour (colour singleton absent). In the trials in which a colour singleton was presented, the colour singleton frequently appeared in a specific colour (50%, called high probability colour); in the other half of the singleton-present trials, a colour singleton appeared in one of the three colours randomly (called low probability colour). The participants were asked to respond by pressing the keyboard as quickly and accurately as possible in both Experiment 1 and Experiment 2. Based on the reaction times, the results showed that (1) in Experiment 1, when the participants were forced to adopt the feature search strategy, they responded significantly faster in the colour singleton-present trials than in the colour singleton-absent trials; (2) in Experiment 2, regardless of whether there was a high or low probability colour condition, the participants responded significantly faster when the colour singleton was present than when it was absent; (3) compared with the low probability colour condition, the high probability colour condition corresponded to significantly faster responses. These results suggest that the influence of statistical regularity on attention is not confined to location, and feature-based statistical regularity of singletons can also modulate the attentional suppression effect.