What Are Illusions?

Chris at Mixing Memory has a post discussing few visual illusions, and also pointing to the announcement of the Best Visual Illusion of the Year.

As illusions came out also in the discussion we had with Richard in the comments, I thought I write a post about them.

What are illusions?

I guess the first intuitive answer would be: “the illusion is when something appears differently from how it is”. For example… two lines are same length, but they appear as having different lengths. Or… some color is gray, but we see it as yellow (check under Colour Perception illusions here). Or, there is no painted skull on the wall, but it seems to us that there is a skull. And so on…

But saying that “things appear differently from how they are”, has certain problems…

To point to one of the problems, I will point to a simple illusion. Take a white ball, for example. The ball is white and seems white. Now shine a red light onto it. The ball seems red, right? But what does “seems red” means there? We can say that white ball when under red light appears same as red ball under white light. But why put priority to how the red ball appears under white light? Why not say that red ball under white light appears as white ball under red light. What is so special about white light?

It seems to me, all we can say here, is that “red ball under white light” and “white ball under red light” appear the same. But if we don’t put priority on the one of those situations, where does the illusion come from?

Let me now propose the different description of what illusions are about, and then try to discuss it further:

Desc*: Illusion:One thing can appear as some another thing even if the things are different. In the course of our lives, we are encountering one of those situations more often, and the other situation usually requires a deliberate setup, or unlikely conditions which rarely occur. So, when we encounter the second situation we tend to judge it to be the first situation.

Illusions are then, not inherent in perception but are problem of the judgment, and usually of our ignorance of the complications in the situation, including the ignorance of the limits of our senses of perception.

So, how this differs from that first explanation that was proposed… Here is I think main differences:

1. That first explanation seems to imply that there is some such entity as “an appearance of a thing”. The logic is, if two things appear as same or similar, there is something identical in both cases, and that which is identical is “an appearance”, then this “appearance” is reified as independent thing, and most likely located in the mind/brain of the subject. (I will explain why in the next point). And because the appearance is something in the mind, to which we have direct access, if there is some mistake it has to be in the appearance itself. Instead of this kind of thinking, in this other way of looking at the illusions, we can negate that there are such things as appearances. Instead we speak about things appearing some way to us, that is, “appear” is used just as a verb and points to a relation between the thing and a person, and not to some other specific entity.

2.When talking about “the appearances” as entities in the previous case, they are imagined as simple, and things to which the subject now has some kind of direct and infallible access. It has to be infallible in this model, because if it is fallible then we haven’t solved the problem at all. Because of this fallibility it will be possible for the “appearance” to appear differently to the subject. And then we need to assume another level of “appearance” and so on…

3.Instead of that, in Desc*, we can include in the picture different properties of the subject’s access to the thing. To be more precise, in one case of appearance,  we can talk about:

  • the intentional content (that to which we access through our senses – it can be a dog, cow, box, etc…)
  • the type of intentional access (e.g. seeing, hearing, etc..)
  • the different characteristics of the intentional access (for example, when we talk about seeing, a person can have glasses, the object might be put under different light or context, there can be fog, can look at the thing from different angles and distances, his eyes might be tired, someone might have rewired some things in the brain, etc…)

All those complications now become possible variables which might be tampered with, in order for something to look like something else.
For example we can say things like “a red ball in normal context appears like a white ball when one sees it through red glasses (or other way around)”, or “two lines with equal lengths drawn on paper with added arrows at the ends, look like lines with different lengths seen in perspective”, or that “gray circle in certain context seems like purple circle in normal context”, or that “a wall after we tamper with our eyes by fixing our eyes to certain color, appears like wall with a circle on it”, and so on…

So, in general there is nothing problematic here that is not present in simple case where a box, and a pyramid can appear same, if we look them from proper side. Things appear same because of limits of our perception, and some of those require a deliberate setup and are rarely encountered, so we will tend to judge such situations as others.

Take for example, a case of afterimage illusions. It requires first fixing your eyes at a specific place for certain time (say 20-30 seconds), and then looking at some blank wall, and not moving the eyes, in order to trick us into making wrong judgment. But we usually don’t make wrong judgment, and say that it “seems” because we are aware that the situation just seems like that other situation (as both situation seem same), and not that it is that other situation.

If you by chance glance towards the sun, it is pretty easy after that to tell that you have problem with the vision. It is not that we are thinking that world has gone weird and some green patch is moving over it.