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-- David Dobbs
, Editor, Mind Matters
Acting on information you didn't know you had
When we choose between two courses of action, are we aware of all the things that influence that decision? Particularly when deliberation leads us to take a less familiar or more difficult course, scientists often refer to a decision as an act of "cognitive control." Such calculated decisions were once assumed to be influenced only by consciously perceived information, especially when the decision involved preparation for some action. But a recent paper by Hakwan Lau
and Richard Passingham, "Unconscious Activation of the Cognitive Control System in the Human Prefrontal Cortex,"
demonstrates that the influences we are not aware of can hold greater sway than those we can consciously reject.
We make countless "decisions" each day without conscious deliberation. For example, when we gaze at an unfamiliar scene, we cannot take in all the information at once. Objects in the scene compete for our attention. If we're looking around with no particular goal in mind, we tend to focus on the objects most visually different from their surrounding background (for example, a bright bird against a dark backdrop) or those that experience or evolution have taught us are the most important, such as sudden movement or facial features -- particularly threatening or fearful expressions. If we do have a goal, then our attention will be drawn to objects related to it, such as when we attend to anything red or striped in a "Where's Waldo
" picture. Stimulus-driven and goal-driven influences alike, then, bias the outcome of the competition for our attention among a scene's many aspects.
The idea of such biased competition
(a term coined in 1995 by Robert Desimone and John Duncan, also applies to situations in which we decide among many possible actions, thoughts or plans. What might create an unconscious bias affecting these types of competition?
For starters, previous experience in a situation can make some neural connections stronger than others, tipping the scales in favor of a previously performed action. The best-known examples of this kind of bias are habitual actions (as examined in a seminal 1995 article by Salmon and Butters
and what is known as priming
Habitual actions are what they sound like -- driving your kids to school, you turn right on Elm because that's how you get there every day. No conscious decision is involved. In fact, it takes considerable effort to remember to instead turn left if your goal is to go somewhere else.
Priming works a bit differently; it's less a well-worn route than a prior suggestion that steers you a certain way. If I ask you today to tell me the first word that comes to mind that starts with the letters mot
and you answer mother
, you'll probably answer the same way if I ask you the same thing again four months from now, even if you have no explicit recollection of my asking the question. The prior experience primes you to repeat your performance. Other potentially unconscious influences are generally emotional or motivational
Of course, consciously processed information can override these emotional and experience-driven biases if we devote enough time and attention to the decision. Preparing to perform a cognitive action ("task set") has traditionally been considered a deliberate act of control and part of this reflective, evaluative neural system. (See, for example, the 2002 review by Rees, Kreiman and Koch -- pdf download
.) As such, it was thought that task-set preparation was largely immune to subconscious influences.
We generally accept it as okay that some of our actions and emotional or motivational states are influenced by neural processes that happen without our awareness. For example, it aids my survival if subliminally processed stimuli increase my state of vigilance -- if, for example, I jump out of the way before I am consciously aware that the thing at my feet is a snake. But we tend to think of more conscious decisions differently. If I have time to recognize an instruction, remember what that means I'm supposed to do and prepare to make a particular kind of judgment on the next thing I see, then the assumption is that this preparation must be based entirely on what I think I saw -- not what I wasn't even aware of.
Yet Lau and Passingham have found precisely the opposite in their study -- that information we're not aware of can more strongly influence even the most deliberative, non-emotional sort of decision even more than does information we are aware of.
Lau and Passingham had their subjects perform one of two tasks: when shown a word on a screen, the subjects had to decide either a) whether or not the word referred to a concrete object or b) whether or not the word had two syllables. A cue given just before each word -- the appearance of either a square of a diamond -- indicated whether to perform the concrete judgment task or the syllables task. These instruction cues were in turn preceded by smaller squares or diamonds that the subjects were told were irrelevant. A variation in timing between the first and second cues determined whether the participants were aware of seeing both cues or only the second.
As you would expect, the task was more difficult when the cues were the not same -- that is, when a diamond preceded a square or a square a diamond. The surprising finding was that this confusion effect was greater when the timing between the cues was so close that the participants didn't consciously notice the first cue. When the cues were mixed but the subjects were consciously aware of only the second instruction, their responses -- and their brain activity as measured by functional magnetic resonance imaging (fMRI) -- indicated that the "invisible" conflicting cue had made them more likely to prepare to do the "wrong" task. Although similar effects
have been shown on tasks that involved making a decision about the appearance of the image immediately following the "invisible" image, this is the first time this effect has been demonstrated for complex task preparation.
It may not be surprising that we juggle multiple influences when we make decisions, including many of which we are not aware -- particularly when the decisions involve emotional issues. Lau and Passingham, however, show us that even seemingly rational, straightforward, conscious decisions about arbitrary matters can easily be biased by inputs coming in below our radar of awareness. Although it wasn't directly tested in this study, the results suggest that being aware of a misleading cue may allow us to inhibit its influence. And the study makes clear that influences we are not aware of (including, but not limited to, those brought in by experience and emotion) can sneak into our decisions unchecked.
Susan Courtney is an associate professor of psychology at Johns Hopkins University, where she runs the Courtney Lab of Cognitive Neuroscience and Working Memory.
Edited by David Dobbs at 11/30/2007 11:26 AM
Edited by David Dobbs at 11/30/2007 11:29 AM