The role of conscious perception in semantic processing: Testing the action trigger hypothesis

Finding that invisible primes affect categorization of visible targets (response priming) is held to demonstrate that semantic processing does not require conscious perception. However, the effects are typically very small, they do not indicate whether conscious perception enhances response priming and they often reflect visuo-motor rather than semantic processing. Here, we compared response priming elicited by liminal words when these were clearly seen vs missed, while participants categorized target animals' names. We varied task demands to induce visuo-motor vs semantic processing. Conscious perception strongly enhanced both visuo-motor and semantic response priming. In line with the Action Trigger Hypothesis, task demands modulated processing of both missed and consciously perceived primes. Finally, conscious and unconscious response priming showed diverging patterns on fast and on slow trials, a dissociation suggesting that priming was not contaminated by conscious priming. We conclude that the impact of unconscious stimuli is small and task-dependent.