Sunday, March 3, 2013

Which priming claims conflict with research on subliminal perception?

I've received several interesting responses to my post on the history of disputed claims of subliminal persuasion. Perhaps the most interesting comment, from a theoretical perspective, was the idea that goal priming does not depend on the stimuli being perceived without awareness. According to this view, priming researchers are not actually interested in testing subliminal perception or persuasion. Rather, they are focused on the more traditional idea from social and cognitive psychology that we lack insights into the reasons for our actions; our behavior is influenced by primes that may or may not be processed without awareness, but we are unaware of the influence of those primes. By that view, presenting the primes subliminally is a means to an end, not an end in itself. As John Bargh wrote in 1992"subliminality of stimulus presentation, therefore, is important not because of the subliminality per se but because one cannnot be aware of the influence of a subliminally presented stimulus."

As I noted in my earlier post, claims of goal priming that do not argue for implicit perception are not controversial from a subliminal perception perspective, and implicit perception folks would not necessarily be skeptical of those.  For example, in their studies in which holding a warm or cold drink influences ratings of personality warmth, Williams & Bargh do not claim that the stimulus itself is implicit. It would be crazy to do so—after all, subjects were asked by the experimenter to hold the drink, so they presumably are aware of the drink and whether or not it is warm. Those studies are focused on a more traditional social psychology question: To what extent are we aware of the reasons or mechanisms underlying our judgments, and do those subtle mechanisms have big effects on behavior. That point is not controversial from an implicit perception perspective since there is no claim of implicit perception, but they are provocative for other reasons (see below). 

If all of the social goal priming research were focused on awareness of influence rather than on the subliminal nature of the stimuli themselves, it would not have inspired as much skepticism from those interested in subliminal perception. After all, the idea that we have mistaken intuitions about the workings of our minds is well established in both social and cognitive psychology.

But, many studies in the social priming literature explicitly claim that the prime stimuli themselves fall outside of awareness, and they use the subliminal nature of the primes to argue that the influence of those primes must occur outside of awareness as well. For example, consider these quotes from Bargh et al's seminal 1996 study of age priming (emphasis added):

"this behavior is unmediated by conscious perceptual or judgmental processes" 
"by the mere presence of environmental features, we mean that the activation of the behavioral tendency and response must be shown to be preconscious; that is, not dependent on the person's current conscious intentions."
"Social behavior is like any other psychological reaction to a social situation, capable of occurring in the absence of any conscious involvement or intervention."  
In their discussion, Bargh et al argue that their study was different from the Vicary "eat popcorn" study/hoax  because the behavioral goals were more relevant, accessible, and not in conflict with other goals (like staying in the theater). In other words, the age-priming study worked because it primed more accessible or actionable goals. Although the implicit nature of the prime is not the core issue for this study, and the result doesn't depend on it, the paper does imply that you don't need to perceive a stimulus consciously for it to have an influence. If conscious access to the prime itself is truly irrelevant, why bother trying to hide it in any way? Why measure awareness of it later?

Other more recent studies in the goal priming literature have made far stronger claims that the primes themselves are subliminal. For example, Hassin et al's PNAS paper claimed:

"We report a series of experiments that show that subliminal exposure to one's national flag influences political attitudes, intentions, and decisions, both in laboratory settings and in “real-life” behavior."
If the subliminal nature of the stimulus isn't central to the claims of goal priming, why claim that it was a subliminal exposure? Why bother presenting it rapidly and masking it? This one falls squarely into the much-disputed implicit persuasion literature, and it lacked adequate controls for awareness of the stimulus: it relied on post-experiment questioning to claim that the primes fell outside of awareness, a technique well-known to be inadequate to rule out awareness of the prime. This lack of proper control for awareness, coupled with claims of implicit persuasion, justify the sort of skepticism I wrote about in my previous post. More broadly, claims of subliminal influence like this one are not unusual—they seem to be accepted and grouped together with other goal priming findings in the literature, which leads me to the conclusion that at least some of the goal priming literature is assuming that the primes themselves fall outside of awareness. 

Another theoretical reason for skepticism

Although claims of subliminal persuasion are perhaps the largest reason for skepticism among those who study implicit perception, there are other theoretically motivated reasons to be skeptical of some recent claims that primes change behavior. Again, the skepticism arrises from a difference in the theoretical perspective of those studying goal priming and those studying other forms of priming. This reason has to do with the purported breadth, power, and persistence of the primes. 

Cognitive psychologists tend to think of priming effects in terms of spreading activation: Primes have a larger effect on closely associated representations and weaker effects on more remotely associated representations. Moreover, the activation diminishes rapidly as the associations become more remote, leading to almost no activation with relatively few steps between the prime and the target. Cognitive psychologists see the links between primes, goals, and behavior as remote, and if they are remote, the influence of a prime should be weak rather than strong. In contrast, goal priming advocates argue for a fairly direct link between primes and goals, with activation of goals directly influencing behavior even when people are not aware that their goals have been triggered by the prime. 

Why might cognitive psychologists question the close link between primes, goals, and behavior? Take what is perhaps the strongest and closest form of semantic priming (i.e., priming of meaning): A prime word leads to faster decisions about a closely related word. For example, seeing the word "doctor" leads to faster processing of the word "nurse." Even that closely related prime requires some spreading activation: Seeing the word doctor spreads to other closely related concepts (nurse), but it produces less priming of "nurse" than it does for "doctor." Such identity priming doesn't require as much spreading activation.

The implicit perception literature shows that it is exceptionally difficult to find evidence for semantic priming of closely related words when people are truly unaware of the prime. That was the focus of my last post. Yet, even with full awareness, a prime does not have a huge influence on semantically related words. In a meta-analysis of semantic priming, closely related semantic associates primed judgments about a related word (e.g., is it a word or not) with an effect size of about r=.21 (Lucas, 2000). Contrast that modest priming (with awareness) for closely related words to the much larger effects of goal priming from words to goals to behavior. For example, the reported effect size for the priming effect of warm coffee on personality judgments was approximately r =.3. It seems implausible to those who study semantic priming that holding a warm cup of coffee would have a bigger effect on personality judgments or pro-social behaviors than seeing the word doctor would have on judgments about the word nurse.

Reconciling the size of social priming effects with the apparently smaller size of explicit semantic priming requires one of three possibilities:

  • The chain of associations linking physical warmth to personality ratings is more direct than that between doctor and nurse. That would require a rethinking of the structure of representations.
  • The mechanisms guiding behaviors in goal priming are different from and more powerful than those underlying other forms of priming.
  • The social priming effects are not as large (or the semantic priming results not as small) as the published reports suggest. 
The first two possibilities would be strong theoretical claims that would require a rethinking of decades of priming research and research on the nature of semantic representations. Although they might be true, such strong claims merit skepticism (not dismissal. skepticism). The third possibility merits direct replication with large samples, preferably by multiple labs, in order to better estimate the true size of the effects. If the goal priming effects prove to be smaller than those for priming of close semantic associates, this second theoretical reason for skepticism would be negated (or at least weakened substantially). Given that the third possibility is the easiest to test and would potentially shore up the interesting claims of goal priming, it seems like the right way to go.