Academic journal article Attention, Perception and Psychophysics

A Task-Difficulty Artifact in Subliminal Priming

Academic journal article Attention, Perception and Psychophysics

A Task-Difficulty Artifact in Subliminal Priming

Article excerpt

Subliminal priming is said to occur when a subliminal prime influences the classification of a subsequent target. Most subliminal-priming claims are based on separate target- and prime-classification tasks. Because primes are intended to be subliminal, the prime-classification task is difficult, and the target-classification task is easy. To assess whether this task-difficulty difference accounts for previous claims of subliminal priming, we manipulated the ease of the prime-classification task by intermixing long-duration (visible) primes with short-duration (near liminal) ones. In Experiment 1, this strategy of intermixing long-duration primes raised classification of the short-duration ones. In Experiments 2 and 3, prime duration was lowered in such a way that prime classification was at chance in intermixed presentations. Under these conditions, we failed to observe any priming effects; hence, previous demonstrations of subliminal priming may simply have reflected a task-difficulty artifact.

The phenomenon of priming without awareness, in which primes escape subjective awareness but nevertheless affect subsequent behavior, has been demonstrated repeatedly in a variety of paradigms. Bargh, Chen, and Burrows (1996) serves as a suitable example: Participants waited longer to interrupt an unresponsive experimenter after unscrambling words that were related to politeness than they did after words that were related to rudeness. Likewise, participants who were exposed to words that were related to old age left the laboratory more slowly than did those who were not.

Priming without awareness, however, is not the same as subliminal priming. Subliminal primes are presented so quickly or in such impoverished conditions that they are not visible, even when full attention is deployed. Clearly, Bargh et al.'s (1996) primes were not subliminal; participants could have maintained awareness of the viewed words and adjusted their behavior as they wished. Cheesman and Merikle (1984) provided the critical distinction between priming without awareness and subliminal priming. They failed to find evidence of subliminal primes; that is, primes that were below an objectively determined threshold did not have an effect on responses to targets.

In the last decade, however, the field has seemingly reversed the Cheesman and Merikle (1984) finding, and many researchers claim to have demonstrated the most impressive form of subliminal priming-namely, that there are priming effects even for stimuli that cannot, under any circumstance, be detected or classified (see, e.g., Dehaene et al., 1998; Greenwald, Draine, & Abrams, 1996; Kunde, Kiesel, & Hoffmann, 2003; Van Opstal, Reynvoet, & Verguts, 2005; see Snodgrass, Bernat, & Shevrin, 2004, for a review). These findings of subliminal priming not only were surprising in their own right, but also influenced theories of human information processing (see, e.g., Greenwald, Abrams, Naccache, & Dehaene, 2003), emotional processing (see, e.g., Li, Zinbarg, Boehm, & Paller, 2008), and mental pathology (see, e.g., Dehaene et al., 2003). Although the claim of subliminal priming is influential, the demonstrations of its existence have been critiqued on statistical grounds (Dosher, 1998; Reingold & Merikle, 1988; Rouder, Morey, Speckman, & Pratte, 2007). In this article, we provide evidence that previous demonstrations may have been susceptible to a subtle methodological artifact that is separate from any statistical critiques.

The subliminal priming claim is conventionally supported by a paradigm with two separate tasks. In one task, participants respond to a clearly visible target. The target is preceded by a briefly presented prime (see Figure 1A), and the researcher assesses the degree to which the prime has influenced the response to the target. In the present experiments, single-digit numbers served as targets, and participants classified them as less than or greater than 5. …

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