Visual and other illusions

 

 Visual illusions vary. Some can be controlled. For example, I find that once I’ve seen both images in a dual-image illusion, I can see either one at will. The two faces vs vase is an example. Of course, I can’t see both images at once: The brain computes the image either as a white one on a black ground, or a black one on a white ground. Hence the illusion.

Others are a trickier, for example the Necker cube illusion. I can trigger the flip, but not entirely at will. I have to blink, so that the brain sees a new input, which will usually be computed the way I want it.

Others are impossible avoid, for example the staggered tiles illusion. The only way to see the horizontal lines as truly horizontal is to cover all except the top row of tiles. There is no way to control this illusion.

Many more visual illusions have been discovered in the last 50 years or so, when neurologists began to wonder why and how they happened. One of the most startling is that colour is always perceived as an illusion. The range of colours in a scene, the distribution of light and shadow, the colours in the light source, the colours of neighbouring regions, all these determine what the brain will compute as the “real” colours.

It’s now known that we suffer illusions in all our senses. The general principle is that the brain computes our perceptions from the filtered, hence limited, data provided by our sensory systems. Some of these computations produce illusions: false or mistaken perceptions. We cannot escape them. At best we can question them. By comparing the inputs from different senses, we can usually recognise hallucinations. Memories can also help do this, but are less reliable. 

Knowledge (gleaned from observation and experiment critiqued and organised with reason) can reveal the reality that the brain miscalculates or fails to perceive at all. But this process is not easy, and above all, it’s slow. It takes patience, experience, and understanding of sometimes opaque methodologies to apprehend the reality beyond the illusion. That reality cannot be perceived, but usually there are procedures to calculate perceivable effects. When these are confirmed by observation, we say that we are now a step closer to the “underlying reality.” The name for the knowledge thus generated is “theories”. 

What’s true of the senses is also true of conceptualisation. A concept is a pattern. We suffer from conceptual illusions just as we suffer visual ones. I think the most pervasive one is that these abstract patterns we call theories are closer to the “underlying reality” that our senses so inconveniently misrepresent or hide from us.