In a recent study, Pratte and Rouder ( 2009) claimed “to provide evidence that previous demonstrations may have been susceptible to a subtle methodological artifact” (p. If, in a separate task that assesses prime awareness, subjects are not able to identify the prime stimuli at better than chance levels (i.e., d′ is not statistically different from zero), then subliminal priming is said to have occurred. If the congruent prime–target pairs dog– tiger and pea– carrot yield faster responses than the incongruent prime–target pairs pea– tiger and dog– carrot, then priming is said to have occurred. Take, for example, an experiment in which subjects have to classify targets as animals or vegetables. A subliminal priming effect is obtained when undetectable prime stimuli modulate target-related processes in some way. The dependent measure is usually response times (RTs) in the case of behavioral paradigms, but the paradigm has also been used by cognitive neuroscientists with a wide range of neurophysiological measures, including event-related potentials (Kiefer & Brendel, 2006), lateralized readiness potentials (Eimer & Schlaghecken, 1998), motor evoked potentials (Verleger, Kötter, Jaśkowski, Sprenger, & Siebner, 2006), and BOLD signal changes in fMRI studies (Dehaene et al., 1998 Kouider, Eger, Dolan, & Henson, 2009 Pessiglione et al., 2007). Importantly, in this paradigm the target stimulus is preceded by a prime stimulus (e.g., the word “dog”) that is related to the target in one way or another. In a standard version of the subliminal priming paradigm, subjects are asked to categorize a target stimulus (e.g., the word tiger) into one of two groups (e.g., “Is it an animal or a vegetable?”). The masked priming paradigm is widely used in the investigation of word and object recognition (Forster & Davis, 1984 Grainger, Colé, & Segui, 1991), as well as in the investigation of nonconscious processes (Abrams, Klinger, & Greenwald, 2002 de Gardelle & Kouider, 2010 Dehaene et al., 1998 Finkbeiner & Palermo, 2009 Pessiglione et al., 2007). Thus, I conclude that controlling for task difficulty does not eliminate subliminal priming. In the prime-classification task, subjects reported the color of the primes very accurately, indicating almost perfect control of task difficulty, but they could not identify the primes. In the experiment proper, priming was observed. To address this possibility, prime words were here presented in color. Essentially, because the prime-classification task is more difficult than the experiment proper, the prime-classification task results may underrepresent the subjects’ true ability to perceive the prime stimuli. In a recent critique of subliminal priming, Pratte and Rouder (Attention, Perception, & Psychophysics, 71, 1276–1283, 2009) suggested that previous claims of subliminal priming may have been due to a failure to control the task difficulty between the experiment proper and the prime-classification task. Nevertheless, there are still those who remain skeptical. The subliminal priming paradigm is widely used by cognitive scientists, and claims of subliminal perception are common nowadays.
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