Research involving subliminal priming tends to instantly grab people's attention, I guess, because there is simply something very enticing, but simultaneously disturbing about the idea that the subconscious might have significant power over our conscience. We don't like to think that we are not fully in control of our own decisions, but we do like the thought that there is some additional hidden computing power behind the choices we make.
That information does not need to become conscious to affect our behavior is experimentally substantiated and popularly accepted. For example, a recent study involved the amount of effort people put into a task depending on the size of a reward they might win for completing the task. The study's results show that people give greater effort if the potential reward is larger, even if the size of the award is only presented subliminally; something we might expect.
An interesting question that arises with these studies, is whether the subconsciously held information is employed simply as an indiscriminate motivation trigger, or whether there is some strategic application involved in how the subliminal information is used. In a way, the question is how smartly we are able to apply subconsciously held information to a situation.
A clever study, investigating exactly this question was this month published in the American Psychological Association's journal Psychological Science.
The study, just as the one already mentioned above, involved the analysis of people's efforts in an incentivized number-retention task, in which participants were asked to remember either 3 or 5 digits for a certain period of time. They were then awarded some monetary prize for correctly recalling the memorized numbers. To measure the mental effort, that participant's put into the task, the study's authors, Erik Bijleveld, Ruud Custers, and Henk Aarts, looked at how widely a participant's pupils dilated during the number-retention task. This method of relating pupil dilation to effort, relies on our physiological understanding of how pupils respond to effort when controlling for other influences on sympathetic activity; possibly material for a different blog post.
The crucial hypothesis behind this experiment rests on the assumption that memorizing 3 digits is sufficiently easy so that a strategic response to an increased reward would not entail greater effort, because the marginal benefit of increasing one's effort is simply too small (i.e. you manage to fulfill the task just fine even without increasing your effort).
Memorizing 5 digits, in contrast, is slightly more difficult, and one might actually expect some additional effort to an increase in the reward size.
Looking first, only at people to whom the reward information was given supraliminal (i.e. to be perceived consciously), the researchers find a pattern that is in support of the above hypothesis. Participants, consciously aware of how high the reward would be, behaved strategically by increasing their effort for the larger reward when the task was difficult (5 digits), but maintaining their effort level when the task was easy (3 digits).
More interesting however is the second finding, which shows this exact same response pattern to hold true also for those people to whom reward information was only provided subliminally. I.e. the strategic application of additional effort only to the task in which the marginal benefit of this additional effort appears worthwhile, occurs for conditions with supraliminal as well as subliminal information.
As the authors state it:
"This indicates that awareness of a reward is not a necessary condition for strategic resource recruitment to take place."
;which is further confirmation that our subconscious is quite savvy indeed. g:-)
Main Reference:
Bijleveld E, Custers R, & Aarts H. (2009) The Unconscious Eye Opener: Pupil Dilation Reveals Strategic Recruitment of Resources Upon Presentation of Subliminal Reward Cues. Psychological science : a journal of the American Psychological Society / APS. PMID: 19788532
