Unconscious inhibition and facilitation at the objective detection threshold: Replicable and qualitatively different unconscious perceptual effects

Although the veridicality of unconscious perception is increasingly accepted, core issues remain unresolved [Jack, A., & Shallice, T. (2001). Introspective physicalism as an approach to the science of consciousness. Cognition, 79, 161–196], and sharp disagreement persists regarding fundamental methodological and theoretical issues. The most critical problem is simple but tenacious—namely, how to definitively rule out weak conscious perception as an alternative explanation for putatively unconscious effects. Using a direct task and objectively undetectable stimuli, the current experiments demonstrate clearly reliable unconscious perceptual effects, which differ qualitatively from weakly conscious effects in fundamental ways. Most importantly, the current effects correlate negatively with stimulus detectability, directly rebutting the exhaustiveness, null sensitivity, and exclusiveness problems [Reingold, E., & Merikle, P. (1988). Using direct and indirect measures to study perception without awareness. Perception & Psychophysics, 44, 563–575; Reingold, E., & Merikle, P. (1990). On the inter-relatedness of theory and measurement in the study of unconscious processes. Mind and Language, 5, 9–28)], which all predict positive correlations. Moreover, the current effects are entirely bidirectional [ Katz, (2001). Bidirectional experimental effects. Psychological Methods, 6, 270–281)] and radically uncontrollable, including below-chance performance despite intentions to facilitate. In contrast, weakly conscious effects on direct measures are unidirectional, facilitative, and potentially controllable. Moreover, these qualitative differences also suggest that objective and subjective threshold phenomena are fundamentally distinct, rather than the former simply being a weaker version of the latter [ Merikle, P., Smilek, D., & Eastwood, J. (2001). Perception without awareness: Perspectives from cognitive psychology. Cognition, 79, 115–134]. Accordingly, it is important to distinguish between rather than conflate these methods. Further, the current effects reinforce recent work [e.g. Naccache, L., Blandin, E., & Dehaene, S. (2002). Unconscious masked priming depends on temporal attention. Psychological Science, 13, 416–424] demonstrating that unconscious effects, although not selectively controllable, are nonetheless mediated by strategic and individual difference factors, rather than being immune to such influences as long thought.