Each of these examples of mental contamination — the focusing illusion, the halo effect, anchoring and adjustment, and the familiarity effect — underscores an important distinction that will recur throughout this book: as a rough guide, our thinking can be divided into two streams, one that is fast, automatic, and largely unconscious, and another that is slow, deliberate, and judicious.
The former stream, which I will refer to as the ancestral system, or the reflexive system, seems to do its thing rapidly and automatically, with or without our conscious awareness. The latter stream I will call the deliberative system, because that’s what it does: it deliberates, it considers, it chews over the facts — and tries (sometimes successfully, sometimes not) to reason with them.
The reflexive system is clearly older, found in some form in virtually every multicellular organism. It underlies many of our everyday actions, such as the automatic adjustment of our gait as we walk up and down an uneven surface, or our rapid recognition of an old friend. The deliberative system, which consciously considers the logic of our goals and choices, is a lot newer, found in only a handful of species, perhaps only humans.
As best we can tell, the two systems rely on fairly different neural substrates. Some of the reflexive system depends on evolutionarily old brain systems like the cerebellum and basal ganglia (implicated in motor control) and the amygdala (implicated in emotion). The deliberative system, meanwhile, seems to be based primarily in the forebrain, in the prefrontal cortex, which is present — but vastly smaller — in other mammals.
I describe the latter system as “deliberative” rather than, say, rational because there is no guarantee that the deliberative system will deliberate in genuinely rational ways. Although this system can, in principle, be quite clever, it often settles for reasoning that is less than ideal. In this respect, one might think the deliberative system as a bit like the Supreme Court: its decisions may not always seem sensible, but there’s always at least an intention to be judicious.
Conversely, the reflexive system shouldn’t be presumed irrational; it is certainly more shortsighted than the deliberative system, but it likely wouldn’t exist at all if it were completely irrational. Most of the time, it does what it does well, even if (by definition) its decisions are not the product of careful thought. Similarly, although it might seem tempting, I would also caution against equating the reflexive system with emotions. Although many (such as fear) are arguably reflexive, emotions like schadenfreude — the delight one can take in a rival’s pain — are not. Moreover, a great deal of the reflexive system has little if anything to do with emotion; when we instinctively grab a railing as we stumble on a staircase, our reflexive system is clearly what kicks in to save us — but it may do so entirely without emotion. The reflexive system (really, perhaps a set of systems) is about making snap judgments based on experience, emotional or otherwise, rather than feelings per se.
Even though the deliberative system is more sophisticated, the latest in evolutionary technology, it has never really gained proper control because it bases its decisions on almost invariably secondhand information, courtesy of the less-than-objective ancestral system. We can reason as carefully as we like, but, as they say in computer science jargon, “garbage in, garbage out.” There’s no guarantee that the ancestral system will pass along a balanced set of data. Worse, when we are stressed, tired, or distracted, our deliberative system tends to be the first thing to go, leaving us at the mercy of our lower-tech reflexive system — just when we might need our deliberative system the most.
The unconscious influence of our ancestral system is so strong that when our conscious mind tries to get control of the situation, the effort sometimes backfires. For example, in one study, people were put under time pressure and asked to make rapid judgments. Those who were told to (deliberately) suppress sexist thoughts (themselves presumably the product of the ancestral reflexive system) actually became more likely than control subjects to have sexist thoughts. Even more pernicious is the fact that as evolution layered reason on top of contextually driven memory, it left us with the illusion of objectivity. Evolution gave us the tools to deliberate and reason, but it didn’t give us any guarantee that we’d be able to use them without interference. We feel as if our beliefs are based on cold, hard facts, but often they are shaped by our ancestral system in subtle ways that we are not even aware of.
No matter what we humans think about, we tend to pay more attention to stuff that fits in with our beliefs than stuff that might challenge them. Psychologists call this “confirmation bias.” When we have embraced a theory, large or small, we tend to be better at noticing evidence that supports it than evidence that might run counter to it.
Consider the quasi-astrological description that opened this chapter. A person who wants to believe in astrology might notice the parts that seem true (“you have a need for other people to like and admire you”) and ignore the parts that aren’t (maybe from the outside you don’t really look so disciplined after all). A person who wishes to believe in horoscopes may notice the one time that their reading seems dead-on and ignore (or rationalize) the thousands of times when their horoscopes are worded so ambiguously that they could mean anything. That’s confirmation bias.
Take, for example, an early experiment conducted by the British psychologist Peter Wason. Wason presented his subjects with a triplet of three distinct numbers (for example, 2-4-6) and asked them to guess what rule might have generated their arrangement. Subjects were then asked to create new sequences and received feedback as to whether their new sequences conformed to the rule. A typical subject might guess “4-6-8,” be told yes, and proceed to try “8-10-12” and again be told yes; the subject might then conclude that the rule was something like “sequences of three even numbers with two added each time.” What most people failed to do, however, was consider potentially disconfirming evidence. For example, was 1-3-5 or 1-3-4 a valid sequence? Few subjects bothered to ask; as a consequence, hardly anybody guessed that the actual rule was simply “any sequence of three ascending numbers.” Put more generally, people all too often look for cases that confirm their theories rather than consider whether some alternative principle might work better.
In another, later study, less benign, two different groups of people saw a videotape of a child taking an academic test. One group of viewers was led to believe that the child came from a socioeconomically privileged background, the other to believe that the child came from a socioeconomically impoverished background. Those who thought the child was wealthier reported that the child was doing well and performing above grade level; the other group guessed that the child was performing below grade level.
Confirmation bias might be an inevitable consequence of contextually driven memory. Because we retrieve memory not by systematically searching for all relevant data (as computers do) but by finding things that match, we can’t help but be better at noticing things that confirm the notions we begin with. When you think about the O. J. Simpson murder trial, if you were predisposed to think he was guilty, you’re likely to find it easier to remember evidence that pointed toward his guilt (his motive, the DNA evidence, the lack of other plausible suspects) rather than evidence that cast doubt on it (the shoddy police work and that infamous glove that didn’t fit).