What does an illusion of x show?

Previous post: what perceptual theories should explain about illusions.

Previous post: universal illusory counterparts

I assume that I am not under a universal illusion. Of course, I would assume that even were I under a universal illusion.

Just as I cannot assume that how things seem is how things are, so I cannot assume that how things seem is not how things are. I agree with Levin 2000 that, although it is possible that I am under a universal illusion, it is also possible that I am not under a universal illusion; further, it is difficult to find evidence that would decide for the former.

If I assume that, then the possibility that I am under such a universal illusion is not something I will try to prove or disprove. What then is the point of discussing universal illusion? To illustrate the following: there can be illusions; a subject of an illusion can fail to detect that they are under an illusion; just because something is apparent does not mean that it is how things are. Thus, if one is naive, and takes all appearances to be how they are (colour? Shape?), one could be misled without knowing it(about colour? Shape?).[1]

And so one might think this: although there may not be evidence of a universal illusion, surely there is evidence that we are capable of being under such a universal illusion. That is, there is no evidence that, for everything I seem to have experienced, all of the object and properties that are or have been apparent to me, are illusory; but there is evidence that I am capable of such illusory experiences, regarding any objects and properties that are or have been apparent to me. That is, based on how I am constituted in this world, I am capable of being misled regarding anything that is apparent to me.

But are we sure there is evidence for such a capacity for universal illusion?

What sort of evidence is there? Well, how about: people hallucinate — even do so easily, given the circumstances, such as a sensory deprivation tank; people experience distortions in sound, smell, sight, and touch; people dream so vividly that they believe, on waking, that it was no dream. People have false memories (and of course false expectations, but this would be a different meaning for ‘illusion’); people have after-images, which they do not know as being ‘in the mind’ (or whatever is going on there) and interpret as being out in the world. By my own analysis (Power 2011, and discussed in the footnotes of this post), Perky’s results suggest people can even have illusions in their imagination.

This plenitude of distortion and misleading appearances suggests that these are only a sample of what goes wrong, for any mode of perception, and that the list of illusions which our perceptual system is capable of extends much further. So, from this, we might conclude that,  our perceptual system is capable of any illusion. For any veridical appearance, there can be a non-veridical, illusory counterpart appearance, i.e., we can assume a principle of universal illusory counterparts.

What can be drawn from an illusion of x

We might conclude this, but it is worth being slow about it. To do so would be equivalent to concluding that, because there are so many ways you can pull apart an object, then one can actually pull it apart in any conceivable way. This would be a controversial assumption, and it ought to be for perception as well. We might conceive of an appearance of P without P being real, but this does not mean that, for any actual subject, there can be an appearance of that P without P being real. It would only follow if one assumed a principle of universal illusion; but the point here is not to assume the principle of universal illusion, but to provide evidence in support of universal illusion.[2]

Instead I think you should only draw the following (here, I mean by ‘y depends on x’, in cases of properties, that for there to be an instance of y, there must be an instance of x):

1. Trivially: each example of illusion, each illusion of an x is evidence that there can be an illusion of that x. That certainly has consequences just from that particular discrepancy between appearance and reality. For that x, its appearance does not mean that we conclude that there is an x. But this does not mean that an illusion of x shows we are capable of an illusion of anything other than x. Unless:

2. Since the appearance of x can occur without actual x, then if the appearance of something else, call it y, depends on the appearance of x, it can occur without there being an x.

To use an example from my 2011, a house can look like a giant castle if its appearance as a giant castle depends, on the one hand, on its apparent shape and, on the other hand, on its apparent distance. If its apparent distance is illusory, it’s ‘giant castle-ness’ will be illusory. One can easily demonstrate dependencies about distance, shape and size, e.g., as seen in Bernard Pras’ work: http://www.bernardpras.fr/

Such illusions, however, do not show illusions which do not depend in this way on x, i.e., some z that is not y. The shape or size of something can be distorted by distortions in distance, but this does not mean that its colour or shade can; one must show something else for that. Nor do they show that these dependent illusions, the ‘y’s, are illusions of the other apparent properties; distance may show the size is distorted, but fail to show the shape is distorted.

Of course, other illusions might do this (and I can think of some that do for the particular examples) but that does not mean that the offered example of illusion shows it. And this should not be surprising. Consider the examples of illusions above, of the Ebbinghaus illusion and the ‘checker shadow’ illusion. From the Ebbinghaus illusion, one can safely infer that the relative size between objects (x) can be illusory. But it is not obvious that one may conclude from the Ebbinghaus illusion what is shown in the ‘checked shadow’ illusion, that a difference in shade can be illusory (y). Further, even if one did think this, it would be because they can show that the differences in shade (y) is in some way dependent on what is illusory in the Ebbinghaus, the differences in size (x), i.e., just the point made here.

3. The opposite dependency relation that is in ‘2’ is this: Unless the appearance of x itself depends on z, then the dependency of x on z does not guarantee that, from the appearance of x, there is a z.

Say that the shape, x, of an object O depends on z, a particular set of three-dimensional properties in physical space, e.g., an object’s apple-shape depends on the object’s ‘fairly-spherical’ three-dimensional properties (this is very rough, I know). If O merely appears to be x, that there is an illusion of x in perceiving O, then from the mere appearance of x, O’s apparent apple-shape, one cannot conclude that there is a z, that O has fairly-spherical three-dimensional properties.

Of course, it might still have those three-dimensional properties. But you can’t take that from its apparent apple-shape, because it really isn’t apple-shaped. If it was really apple-shaped, then you could conclude that it had those three dimensional-properties. But then there would be no illusion here of the apple shape, the x in this example.

From ‘1’, ‘2’, and ‘3’, one can draw other conclusions: mutually dependent properties are combinations of ‘2’ and ‘3’. The point is, other than these three conclusion, I am not sure what else one can draw from an illusion of x. (Suggestions are welcome).

Illusions of space and time

Someone might wonder: so what?  This is all very well if one did not know the following:

There can be illusions of fundamental properties, properties on which most other properties depend. These are properties of space and time — that is, there can be illusions of space and illusions of time.

Thus, there can be illusions of any properties dependent on their occurrence on spatial and temporal properties (or their appearance on the appearance of spatial and temporal properties).   Most properties, especially in the phenomenology of perception, depend on spatial and temporal properties.

And there are lots of instances of illusory spatial and temporal properties.


It’s Now Over There: illusions of space (there) and time (now)(in development)

Illusion and the embedded and extended mind debate

1. Some philosophers (e.g., Crane 2006, Tye 2007, and Harman(discussed in Lycan 1996)) claim that, in having an experience, what is apparent to us, e.g., what we seem to see, hear, touch, etc., seems not to belong to the experience itself, but only to belong to things in the external world, independent of experience itself. The experience’s own properties are not apparent to us at all. Tye refers to this as the ‘transparency’ of experience; Crane refers to it as the ‘diaphanousness’ of experience.

One point I think could be drawn from the issue with illusion is that, even if it seems that way, that experience is transparent, that we only experience properties of external things, we possibility of universal illusion means that cannot be sure that it is that way. But, again, it does not mean that we cannot be sure that it is not that way either. My point throughout is that, without actual evidence for one or the other, I think one has to either throw up one’s hands and then sit on them about the whole affair, or draw on the only thing available to prefer one or ther other: appearances themselves, that it seems that way.

[A footnote to the footnote: on the claim that transparency/diaphanousness -> we do not experience the properties of experience themselves.

Because I am interested in the structure of experience, in how it is constituted and its spatiotemporal conditions, and, further, I am sympathetic to positions involving an object being necessary and presented for experience (somewhat in the spirit of naive realism and indirect realism) I tend to take it that, in one way at least, it should be an open possibility that we experience properties that  strictly (though indirectly) belong the experience.

These are properties of the object of experience under a conception of the experience/object relation as one where the object is a constituent of the experience. In that case, one might say that we experience a part or constituent of experience, the part being the object of the experience, or its properties. If we think of the whole inheriting the properties of its parts (e.g., a woolly mammoth is woolly — except, of course, only part of it is woolly(its tusks, eyes, and toes aren’t)), then we are in this sense experiencing properties of the experience.

I think is reasonable to think that is a metaphysical claim about experience; it is not a naive claim, or simply pointing out the phenomenology of experience, i.e., how we describe it. But I also think that the alternative is not a naive claim, a simple pointing out of the phenomenology, either: that, conceiving of experience as something that happens,  then experience is something completely separate to what we experience, what we experience is not part of experience.

After all, the very motivation for transparency/diaphanousness is that the phenomenology, in having an experience, is only of the object and its properties, of what we experience. In ignorance of the complex processes involved in experience, one might think that all there is to experience is what is experienced; all that is happening is only what we are experiencing. In that case, one experiences the properties of experience because the only properties experience has are the properties of what we experience.

Of course, I do not assume that this is true, nor do I expect anyone else to assume it in this debate. But I do not think it is false because experience is separate or separable from what we experience. It is my view that, for various reasons, one might want to develop an account of experience that says experience includes the properties of what we experience, and more, rather than excludes those properties (which are, again, the only ones of which we are aware in having an experience).

(I will say more about this in a later post)]

2. One might think that the fact we are talking about appearances means automatically that there can be an illusion. That is, an: appearance of x -> possibly ( illusion of x).

First, as the discussion so far should show, the issue doesn’t just concern the possibility of illusion. It concerns there being evidence that, given how our actual perception works, that, for a particular x, x can appear without being real.

Second, it is true that ‘appearance’ and ‘not real’ are compatible, that ‘apparent(x) and ~x’ is a coherent phrase, and that an entity can have the concept of ‘appearance’  and ‘unreal’ or ‘not real’ coherently applied to it (in contrast, the special concept I introduce as ‘obviousness‘ is not compatible with ‘not real’; ‘obvious(x) and ~x’ is incoherent — as incidentally is ‘obvious(x)’ and ~apparent(x)’). But that something is conceivable, again, does not mean we have to satisfy it with our explanations about how actual perception works (something similar is argued by Harman, discussed in Arstilla 2005). 

(I can think of at least one group of theorists should agree with this last point: those who hold that some apparent properties are only apparent, without there being any case where they correspond to something real, e.g., representational physicalists who agree that qualia  (1) are apparent and (2) are non-physical but reject having to accept them as something real (e.g., Dennett 1991, perhaps; Lycan 1996; discussed by Crane 2006).  For reasons that have been touched on so far, I think one should resist approaching the problems of consciousness in this way, but never mind that now).


4 thoughts on “What does an illusion of x show?

  1. Pingback: What illusions do theories of perception have to explain? « Time and Illusion

  2. Pingback: Complexity and illusion « Time and Illusion

  3. Pingback: Illusion and the embedded/extended mind hypotheses « Time and Illusion

  4. Pingback: Spatial illusions and temporal illusions (I): Three Dimensions | Time and Illusion

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