We all love the old cowboy movies. The good guys and their white hats. We hate the bad guys who all have black hats. How is this possible? The screen is white and it is impossible to project black. Black is the absence of colour. The projector can only leave a gap where the black should be. We should therefore see the blank, white screen. Our brain creates the reality of black. This is due to the brains’ amazing capability for perceptual completion. Our senses do not exist in isolation from our brains and memory, they are an integrated whole.
We tend to think of our senses as neutral measurement instruments. Our eyes are thought of as some form of camera that sends pictures to the brain. Our ears are microphones. The senses deliver undistorted reality. Nothing could be further from the truth. Our perception is not reality. We inhabit a personal virtual world created by our brains to maximize our chance of survival.
We blink on average fifteen times a minute. We never experience a moments interruption to our vision. In each eye there is a blind spot where the optical nerve attaches to the retina. In an area a few millimetres across there are no sensors. Even as an infant, we never experience the blind spots. Our brains are making compensatory adjustments.
Our lenses are a masterpiece of evolution. Physicists know that they cannot produce straight and parallel lines across our whole field of vision. Our mind makes sure that buildings do not bulge. When someone wearing a red shirt walks inside from bright sunlight to a room lit artificially, we see no change in colour. The difference in the frequency of the ambient light should change the colour.
The brain compensates for the other senses as well. If we touch a wall with our toe and finger simultaneously the signals cannot reach the brain at the same time. The one from the toe must travel further. This would be extremely confusing; perception merely equalizes the signals.
Perception can subtract as well as add. New odours are stronger to us when we first experience them. If we have continued exposure, then the smell “fades into the background”. The first day working on a pig farm is the worst. Repeated exposure means we do not notice any more. Our sense of all other smells meanwhile does not change. The effect reverses if we no longer work in the smell all day. Our sensitivity to that smell increases again. Taking a holiday can make the first day back on the farm unpleasant again.
Sometimes perceptual completion is not so helpful. The latest theories on tinnitus suggest that perceptual completion may be the cause. Tinnitus is a ringing in the ears that affects one in five adults. For some it is a minor distraction, for others a chronic disease. As hearing declines, the brain can be starved of input at certain frequencies. The latest ideas suggest that perceptual completion creates the ringing to complete the sound picture. The ringing is in the brain not the ears.
Reality is Just a Guess
To survive in our evolutionary past, we needed to recognize danger. Our brain learned to create the reality we needed. All the senses operate together in real time. The brain is searching for a pattern it recognizes. It iterates through all the senses and its associative memory looking for a fit. Perception is a constructive process. The brain is constructing a mental image that best suits us now. As it starts to get “a fit”, the brain redirects the senses to areas of the “scene” that need to be better defined.
The information received from the senses is always incomplete. Receptors may be faulty, more so as we age. The scene may have interference. A conversation in a crowded room must be distorted by the background noise.
Perception starts with what it has and then compares it with an accumulation of memories. It then uses problem solving and inference to find a fit. If that fails, it guesses. Our reality is not real and is just a guess.
Ageing Helps Perception
Perceptual completion comes to the aid of the Third Age consumer. Our senses fade with age. Not everybody loses a particular sense. Few people suffer deterioration in all senses. There is huge variability across individuals. The thresholds increase for those senses so that we need more stimulus: light, sound etc to react. Despite this perception is able to maintain our “virtual reality” for many years .
The ageing actually helps perception. We have a much greater collection of memories and scripts on which to draw. We have “seen it all before”. This improves the chances of our perception finding a fit in our associative memory. Age brings more experience at categorizing and abstracting. Both of these are essential parts of the pattern recognition process.
Age brings with it wisdom. We are able to see patterns that younger people cannot recognize. We are more emotionally stable. We are better at “pattern recognition” in stressful situations. Perception can use all of this to maintain our reality. If necessary, it will guess more. From the age of forty our perception increasingly depends upon our brains and not our senses. We really are in a virtual world of our own.
The Invisible Decline of the Senses
Because of this, self-awareness of the sensory loss is low. It is an extremely poor predictor of the actual state of our senses. In a fifty-five-year-old age group of women with proven clinical decline in their sense of smell, only one third said they had a problem. This dropped to twelve percent for the above eighty age group. The gap gets bigger as we get older. Our memories are increasingly driving our perceptions.
According to medical science the amount of light falling on my retina is less than half of someone half my age. Despite this I do not perceive myself walking around in the dark. My brain can fill in most gaps. Unfortunately, not all of them. I still cannot read the menu in a darkened restaurant. The input my eyes can provide, even with glasses is too low. Perhaps it is the brain that is no longer powerful enough to even make a guess?
Certainly, older people complain more and more about distraction. They complain about the noise is bars and restaurants. “I cannot hear myself think”. This may be truer than they think. Coping with distraction requires “multi-tasking”. We must filter the noise out whilst studying the menu and deciding what to eat. With age multi-tasking becomes more difficult. Is it easier to overwhelm the brain with too complex environment full of multiple stimuli.