In the hands of metacontrast: Investigating the dual-task structure of an unconscious priming paradigm

Our study investigated unconscious priming from a dual-task perspective by means of a metacontrast masking paradigm with trial-by-trial assessments of prime visibility. Participants responded to target stimuli via keypress. In the prime-related direct task, they responded via vocal response (cross-modal) or keypress (unimodal), using either high (four-item) or low (two-item) complexity subjective or objective visibility measures, and responded with either one or two hands. We tested how these manipulations affect response times (RTs) and error rates. In two out of three experiments, participants were unaware of the prime at the shortest stimulus-onset asynchrony (SOA), with visibility measures increasing at longer SOAs. RTs were consistently longer in dual-task than single-task conditions. Priming effects were comparable across task types in Experiments 1 and 2, but larger in dual-task conditions in Experiment 3, likely due to increased prime visibility. RTs were also prolonged in unimodal and high-complexity conditions, while two-hands responses led to faster RTs. Priming effects were larger in unimodal conditions, but unaffected by complexity. Hand usage did not affect priming in Experiment 2, but in Experiment 3 where two-hands responses led to increased priming effects. Taken together, our findings highlight the important role of task characteristics like modality, hand usage and complexity in the design of masked priming experiments. We recommend careful consideration of these factors when employing unconscious priming paradigms with trial-by-trial prime visibility judgments, as such paradigms continue to advance our understanding of unconscious cognitive processing.