What every skeptic should know about subliminal persuasion

Thus, ample evidence attests to the fact that much of what goes on in the mind is unavailable to conscious awareness. Note, however, that the "elderly words" experiment, as well as the research on stereotype activation, used stimuli that were, or could have been, consciously perceived. Since this article's primary concern is the influence of subliminal stimuli, we turn to whether subliminally presented stimuli can actually be perceived, while still remaining unavailable to conscious awareness.

We believe that the research literature leaves little doubt that the answer is yes. Many researchers have reported, for example, that words presented subliminally can influence subsequent judgments. Dixon (1981, see also Epley 1998a) found that participants given a subliminal prime (e.g., the word pencil) were faster than those who had not seen the prime to later identify a related word (e.g., write). Likewise, Marcel (1983) found that participants' identification of a color on a computer screen was facilitated when it was preceded subliminally by the name of the color, but was delayed when preceded by the name of a different color. Although these early studies have been criticized on methodological grounds (Holender 1986; Merikle 1982), similar effects have been found using methodologies developed to address these criticisms (Greenwald Draine, and Abrams 1996; Greenwald and Draine 1997; Merikle and Joordens 1997).

In all, dozens of studies using implicit tests of perception now attest to the fact that subliminally presented stimuli can be perceived (for reviews, see Bornstein and Pittman 1992; Greenwald 1992). But can they persuade?

Ghosts In the Machine: Subliminal Influences on Cognition

For many, the Eiffel Tower is a beloved symbol of Paris. But this was not always true. When the structure was built in 1889, it was despised by many - some Parisians even advocated its destruction (Harrison 1977). Likewise, popular reactions to new artistic movements that are now cherished, from Impressionist painting to rock and roll music, were initially negative (Sabini 1995).

How can these changes of heart be understood? One answer has been proposed by Robert Zajonc (1968), who suggests that "mere exposure" leads to liking: The more one sees something, the more one comes to like it. Thus, the more times people were exposed to the Eiffel Tower, paintings by Monet and Renoir, and the music of Elvis and the Beatles, the more positive their evaluations became.

Experiments have demonstrated that this mere exposure effect is reliable, and, furthermore, that the phenomenon does not depend on one's conscious awareness of the exposure. In one study using subliminal stimuli, for example, participants were shown several irregular polygons for one millisecond, five times each. In a subsequent phase of the study, they were given pairs of figures, one that had been flashed to them previously and one they had never seen. Participants were then asked to make two judgments: which one had they seen before, and which one did they liked better. Although they were unable to determine which figure they had seen (these guesses did not depart reliably from a chance base-rate of 50 percent), participants did show an increased liking for the familiar shapes, preferring them 60 percent of the time (Kunst-Wilson and Zajonc 1980; see also Epley 1998b; Seamon, Marsh, and Brody 1984).