Not only are we likely to get things wrong just because the equipment is faulty, our prior ideas can predispose us to get things wrong in a particular way. Think of it as a sort of built-in confirmation bias; our brains are set up in such a fashion that when we've already decided what's going to happen, it's much more likely that's what we'll perceive.
This latter problem was demonstrated in an elegant, if disturbing, fashion in a paper released last week in Science called "Pavlovian Conditioning–Induced Hallucinations Result From Overweighting of Perceptual Priors," by Albert R. Powers, Christoph Mathys, and Philip R. Corlett, of the Yale School of Medicine, the International School for Advanced Studies (Trieste, Italy), and the University of Zurich, respectively. Their research springboarded from previous studies wherein individuals who had been trained to associate a tone with an image were more likely to continue "hearing" the tone when shown the image with no accompanying tone than were members of a control group.
[image courtesy of the Wikimedia Commons]
The results were intriguing, to say the least. Both the schizophrenics and the self-described psychics were five times as likely to report hearing a tone when none existed than either the control group of healthy individuals or the psychotic individuals who did not hear voices. Not only that, the schizophrenics and the psychics were 28% more confident in their perceptions when they did hear a tone that wasn't there than were the other two groups when they made a similar mistake.
Further, the schizophrenics and psychics showed abnormal neuronal activity in two regions of the brain; the parts of the cerebrum involved in creating our internal representation of reality showed strikingly different firing patterns, and the cerebellum -- the part of the brain involved in planning and coordinating our motor responses to stimuli -- showed much lower than normal neuronal activity.
"The findings confirm that, when it comes to how we perceive the world, our ideas and beliefs can easily overpower our senses," said Albert Powers, one of the paper's authors. Which is about as succinct a cautionary statement about trusting our judgments as I can imagine.
While the researchers specifically tested the likelihood of experiencing auditory hallucinations, I find myself wondering if this study might not have wider applications. How do our prior perceptions bias us in general? I know I have frequently been baffled, especially in these fractious times, how two people can see the same event and come to strikingly opposite conclusions about it. At times, I have found myself asking, "Are we even talking about the same thing, here?" But if our preconceived notions about the world can bias us strongly enough to hear sounds that aren't there, why should any other perception be immune to the same effect?
This possibility drives me to a disturbing conclusion. How do you convince people that what they're perceiving is not real, if that conclusion is contrary to what their senses and their brains are telling them?
I think the key, here, is always to keep focused on the statement, "... but I might be wrong." A lot of our faulty judgments are caused not only by our coming to the wrong conclusion, but our stubborn certainty that we are, in fact, right. A willingness to revise our beliefs -- failing that, at least to consider the possibility that our beliefs are incorrect -- is absolutely critical.
Otherwise, we're at the mercy of sensory apparatus that are easily fooled, and a brain that bases what it perceives as much on what it already thought to be true as on the actual data it's presented with.
Which seems to me to be awfully shaky ground.