When we look at the world, what do we see?
We see what makes sense to us, and what we are comfortable with. Research into how the brain processes sight gives added emphasis to this concept because a large portion of what we perceive is manufactured by processes below our level of awareness.
This is true both physically and mentally.
Physically, humans have a blind spot. There are no photo receptor cells at the back of the retina where the optic nerve connects to the eye. Technically, it is called the punctum caecum. One of the brains best tricks is its ability to seamlessly fill in this blind spot based on surrounding information.
If we stare at a simple yellow wall or a detailed photograph, one’s brain fills in the blackness in the middle of our vision. Look closely, which part is manufactured and which part is real? It’s impossible to say. This spot is only five degrees wide but it exists nonetheless.
How clever this mechanism is can be demonstrated by the simple fact that it only came to light in the late 17th century. It was thought at that time that vision should be sharpest at the point where the optic nerve attached to the eye. Experiments were done to prove this. Factually, it was the opposite.
The phenomenon was first demonstrated by the French physicist and priest, Edme Mariotte, in the 1660s. He amazed the French court when he made a coin disappear from view by placing it in the blind spot.1
Even today, sight is commonly believed to be one-way, the result of light entering the eye, being captured by light sensitive cells, and then converted to electrical impulse. These impulses are shunted to the brain where they are combined with the data from the other eye. The brain then further processes the information into a three-dimensional rendering which we perceive.
This theory of sight is fairly universal. It has also influenced our perception of the world.
The phrase ‘seeing is believing’ is supposed to be true, but with more study and starting with the interpolation of the blind spot, it has become apparent that sight is a two-way process with information moving both up and down the optic nerve rather than simply moving in one direction.
Not only do we not see what really exists before us, but how we think about the things we see alters them to the point that our ideas about our past are likely to be very different from actuality.
In the American legal system, the honest recounting by eyewitnesses of what they have seen and heard has been an important factor in sorting the truth or falseness of witness statement by juries and judges. While deliberately lying to a court or to an investigative authority is a crime and punishable under the laws of perjury, misremembering is not. Just the same there is no guarantee that what is being related is the whole truth and nothing but the truth.
Eyewitness testimony has been found to be fallible in a number of ways:
Witness memories can be manipulated.
In the 1970s, experiments were conducted that found that false facts could be introduced into a person’s memory by a third party.
Subjects were shown slides of a car at an intersection where there was either a yield sign, or a stop sign. Sometime later the researchers asked questions about the presence of a stop sign, when there was in actuality a yield sign. At other times they asked about a yield sign when there was a stop sign. In both instances, witnesses were far more likely to remember the false image than the factual one.
Additionally, they were often more certain about the false memory than the correct one.
In another series, subjects viewed slides of a car accident. Some were asked how fast the driver was travelling when they ‘hit’ the other car, and others were asked how fast the car was traveling when it ‘smashed into’ the other car. Those that were asked about the car smashing into the other were more likely to remember seeing broken glass in the slide, when in fact none was present. 2
How can this be?
Perhaps the best way to answer this question is by pointing out that much of life is predictable. Our brains have limited processing power.
The idea that we only use 10% of our brain is patently false. Our bodies have a lot going on.
Take the simple act of sleeping. This is like flying an aircraft on autopilot. Breathing has to be maintained as well as the monitoring of heart rate, digestion, immune system, balance, salinity, and a host of other functions. The brain carries on monitoring and controlling regardless.
When awake, the outside world offers both threats and rewards. We think. We plan. We experience. Each of these takes processing power and, for the most part, we are limited in the number of things we can think about and process at any given time. The maximum is usually five to seven. After that we tend to freeze up. The brain overloads unless it can relegate some of the tasks to auto mode whereby learned behavior takes over, and we no longer have to think about it. But in order to do this effectively and not have the autopilot kick off and the action turned back over to conscious thought, surprises must be kept to a minimum.
For this to happen, the brain relies on much of what we perceive as being stable and predictable. How many times have we driven home from work only to not remember how we managed it because when asked to recall the details we could hardly remember one? Can you recall all the things you did this morning in sequence?
We see and recall what we expected to see because much of what happens around us happens on a regular basis. If life was completely unpredictable how could we survive?
Imagine having the scene before you change every few seconds. One moment you are at the beach. The next moment you are in the mountains. The next you are in a room. Your brain relies on the fact that things will not change too drastically from one moment to the next. How else could it fill in that blank spot? Without the ability to interpolate, we would be too stressed to survive. 3
Witness memories change.
When we recount an incident, the reason for telling the story plays a part. If we are asked at a friendly gathering to relate an amusing incident when we spilled soup at a dinner party, that story would be different from the one we would tell the police if questioned sharply about it.
Memory, it seems, is pliable and distorts with retelling. Recounting actually changes our reality, morphing it into a shape and a substance that we are most comfortable with. 4
Take for instance the memory of an expert trader. The trader recalls buying a particular stock many years ago at a particular price and watching it go up to four times his buy price before it falls back to well below the price he bought it. It is one of his stories that has motivated him to really study markets. Looking over the actual prices at that time finds a radically different picture. The true data is so different from his memory (and he points out he would have bet money that his recall was correct), he concludes his entire past is likely to be a fabrication of his brain. How many of our own stories are just like this one? 5
In the Tversky-Marsh study, eyewitnesses of a violent film scene were asked to recount what they saw. The conclusion was that the act of relating the event leads to memory changes; in addition, the greater the number of retellings, the greater the changes. 6
Memory, it seems, is a not simply a record of the past but a living thing that changes as we change. What we perceive is not simply a record of the world but a combination of reality and the experiences we put there.
Although these findings may downplay much of the importance of witnessed behavior, it opens up a much more interesting view of the human mind. We are not simply a walking hard drive but something a lot more complicated.
1. Eagleman, D. M. (2011). Incognito, The Secret Lives of the Brain. New York, NY: Pantheon Books
2. Engelhardt, L. (1999). The Problem with Eyewitness Testimony, a talk by Barbara Tversky, Professor of Psychology and George Fisher, Professor of Law, Stanford Journal of Legal Studies, retrieved June 14, 2013 from http://agora.stanford.edu/sjls/Issue%20One/fisher&tversky.htm.
3. Eagleman, op. cit.
4. Marsh, E., Tversky, B., Hutson, M.,(N.D.) How Eyewitnesses Talk about Events: Implications for Memory. Retrieved June 14, 2013 from http://psych.stanford.edu/~bt/memory/papers/marsh-tversky-hutson_eyewitness.pdf.
5. Tharp, V. K., (2013). Poloron Products: A Follow Up To My Faulty Memory. Retrieved June 14, 2013 from http://www.vantharp.com/Tharps-Thoughts/631_May_29_2013.html
6. Tversky, op. cit.
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