Abstract
In priming research, it is often argued that humans can discriminate stimuli outside consciousness. For example, the semantic meaning of numbers can be processed even when the numbers are so strongly masked that participants are not aware of them. These claims are typically based on a certain pattern of results: Direct measures indicate no conscious awareness of the masked stimuli, while indirect measures show clear priming effects of the same stimuli on reaction times or neurophysiological measures. From this pattern, preserved (unconscious) processing in the indirect task is concluded. However, this widely used standard reasoning is problematic and leads to spurious claims of unconscious processing. Such problems can be avoided by comparing sensitivities of direct and indirect measures. Many studies are affected by these problems, such that a reassessment of the literature is needed. Here, we investigated whether numbers can be processed unconsciously. In three experiments, we replicated and extended well-established effects of number priming over a wide range of stimulus visibilities. We then compared the standard reasoning to a sensitivity analysis, where direct and indirect effects are compared using the same metric. Results show that the sensitivities of indirect measures did not exceed those of direct measures, thereby indicating no evidence for preserved unconscious processing when awareness of the stimuli is low. Instead, it seems that at low visibility there is residual processing that affects direct and indirect measures to a similar degree. This suggests that similar processing modes cause those effects in direct and indirect measures.
Highlights
In the past decades, research on unconscious priming has received increasing attention
We focused on the behavioral part of the original studies (Dehaene et al, 1998, had conditions with EEG and fMRI), since most researchers in this field measure reaction times (RTs) in the indirect task
Participants performed close to chance level with 54% correct. This performance is almost identical to the direct task performance in Dehaene et al (1998), who reported 56% correct and 54% correct in their two direct tasks
Summary
Research on unconscious priming has received increasing attention. Participants directly classify a masked stimulus (“prime”) and perform close to chance. Participants respond to a “target” stimulus following the masked prime and the prime has clear and significant effects on reaction times (RTs) or brain activity (EEG, fMRI). From such a pattern of significant priming effects in the indirect task and close-to-chance performance in the direct task, researchers typically infer that there is better sensitivity to the stimulus categories of the prime in the indirect than in the direct task. It is widely applied to unconscious priming research and the results derived from such studies have a
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