Illusion / delusion / hallucination

[Dr B]

There is often a great deal of confusion - amongst believers and some skeptics - over the role of illusions, delusions, and hallucinations in the paranormal etc.

I thought the following views might help as they reflect the main central themes from science. There are some that disagree with what I am about to say - but most scientists working in the field would recognise and endorse something along the following lines.

An illusion (as in a perceptual illusion) is not the same as a delusion and both are somewhat dissimilar to hallucination. An illusion is seen as a forced mis-perception or the perception of implied objects and object relations etc. They reveal how the brain goes far beyond the sensory data when constructing perception.

A delusion is the incorrect attribution or interpretation of stimuli - like a false-belief. A good example is Capgras syndrome - where patients suffer a delusion of familiarity and think that people who should be familiar to them have been replaced. It is a fantasy. In this sense one can arrive at a delusional interpretation of ambiguous stimuli (dripping tap = footsteps etc). So there can be a real external stimulus of some sort - but the resulting interpretation is false. Also alien-hand syndrome is often seen as a delusion (a misattribution of the agency of ownership, volition and action)
These instances above are not hallucinatory and it would be wrong to think of them as such (in a classical sense).

Hallucination is generally thought of as being purely internally driven - having no veridical external stimulus. It is the imagined - seen as perception. The problem is further compounded when it is realised that hallucinations can be called 'pseudo-hallucinations' or 'real hallucinations' - only in the latter circumstance is the hallucination treated as real (i.e., a reality to rival perception). It is entirely possible to hallucinate and not think it is real at all. From this, one could argue that 'true-hallucinations' can be seen as part hallucination and part delusion as, for it to be seen as real, this must be a false belief. It is a fair point - but this is where a great deal of confusion lies.

The point is - some paranormal experiences are more delusion than hallucination. The reason it is so important to be clear on these distinctions is that they require separate neurocognitive mechanisms to occur and so, while one may be able to rule out hallucination, say because 10 people heard the noise (- though this does not entirely rule hallucination out at all... :cheesy:) the experience could still be explained as being due to a deluional interpretation of that noise. In this latter sense - there really was a noise - but the interpretation may well be fanciful. O0

[Cuddles]

Interesting. The only phenomenon I've ever experienced is waking up in a dark room to see someone leaning over me, that turns out to be a coat hanging on the door. I'd always assumed that would be called a halucination, but according to this is would be a delusion.

I'm not sure I agree with illusion being different though. An illusion takes a real physical input and interprets it as something different, which seems to be exactly the same as a delusion. The only difference is that an illusion is often constructed deliberately and is repeatable and viewable by others, while delusion tends to refer to one-off events.

Edit: Incidentally, is the other thread that looks just like this one an illusion or hallucination?:tongue:

[MRT]

A delusion is the incorrect attribution or interpretation of stimuli - like a false-belief. A good example is Capgras syndrome - where patients suffer a delusion of familiarity and think that people who should be familiar to them have been replaced. It is a fantasy. In this sense one can arrive at a delusional interpretation of ambiguous stimuli (dripping tap = footsteps etc). So there can be a real external stimulus of some sort - but the resulting interpretation is false. Also alien-hand syndrome is often seen as a delusion (a misattribution of the agency of ownership, volition and action)
These instances above are not hallucinatory and it would be wrong to think of them as such (in a classical sense).

Now you've got me confused! I would have said a 'dripping tap = footsteps' was an auditory illusion! Similarly, I thought 'alien hand' was more of an illusion. I base this on the idea that an illusion is where the brain is fooled by ambiguous sensory input into misinterpreting what is real. I thought delusion was an actual 'fault' in the way the brain is interpreting the world, with no sensory input required. In other words 'illusion = sensory mistake', 'delusion = brain functioning mistake'. Perhaps you could clarify, please, DrB?

[wooo_oops]

Interesting. The only phenomenon I've ever experienced is waking up in a dark room to see someone leaning over me, that turns out to be a coat hanging on the door. I'd always assumed that would be called a halucination, but according to this is would be a delusion.

Hm. Now I would've said that was an illusion.:-\

An illusion (as in a perceptual illusion) is not the same as a delusion and both are somewhat dissimilar to hallucination. An illusion is seen as a forced mis-perception or the perception of implied objects and object relations etc. They reveal how the brain goes far beyond the sensory data when constructing perception.

[Cuddles]

Hm. Now I would've said that was an illusion.:-\

I was going more for this one:
A delusion is the incorrect attribution or interpretation of stimuli - like a false-belief.
However, I think this kind of reinforces my point that these definitions mean illusion is basically a special case of delusion rather than a seperate phenomenon.

[MRT]

I suspect the problem with overlaps is because many illusions are neuro-physiological. Perception takes place largely in the brain which is also the seat of delusions. Optical illusions, for instance, resemble a sort of reflex reaction in the brain which we cannot control. Delusions are, by contrast, false beliefs which affect how people deal with the world but not what they actually see or hear.

[Dr B]

Now you've got me confused! I would have said a 'dripping tap = footsteps' was an auditory illusion!

No - it's a high-level false belief. An erroneous interpretation thus a delusion. These delusions are more of a high-level attribution (or mis-attribution if you will). An illusion is not a belief or attribution - it's an unavoidable perception (more low-level and perceptual). Like the muller-lyer illusion - you cannot avoid seeing it. This is not an interpretation in the true sense of the word.


Similarly, I thought 'alien hand' was more of an illusion.

Definately not! Alien hand syndrome is a delusion - a high-level mis-attribution.


I base this on the idea that an illusion is where the brain is fooled by ambiguous sensory input into misinterpreting what is real.

We have no idea that the input in alien-hand syndrome is ambiguous - its the higher-level attributional processes where this breaks down.


I thought delusion was an actual 'fault' in the way the brain is interpreting the world, with no sensory input required.

Not quite - it does require sensory input - otherwise it is hallucination :cheesy:

Seems like this discussion is going to be more of use than I thought!!!!

[Dr B]

I'm not sure I agree with illusion being different though. An illusion takes a real physical input and interprets it as something different, which seems to be exactly the same as a delusion. The only difference is that an illusion is often constructed deliberately and is repeatable and viewable by others, while delusion tends to refer to one-off events.


Hiya Cuddles

A delusion, dont forget, replaces reality and thus 'deludes' one. An illusion does not replace reality. I would describe your example as an illusion (implied via ambiguous sensation) - if you still believed it to be a real person / ghost - then that would be furnished with further delusory interpretations and thus may, over time, morph into a delusion.

[Dr B]

However, I think this kind of reinforces my point that these definitions mean illusion is basically a special case of delusion rather than a seperate phenomenon.

No - it is a separate phenomenon in the brain. Illusions only require early low-level processing to occur. A delusional belief requires none of this and can exist in the absence of an illusion.

An illusion may trigger a further cascade process (over time) and lead to a delusional belief - but the formation of that belief and the content of it are independent of the processes giving rise to the illusion.

There will always be circumstances that feel more difficult to define - but it is important to first understand what the correct terminology is before one can decide how to label it, or indeed if such labels are useful.

Bentall (for example) has argued against many definitions in the DSM - and I agree with him on most of them O0. Bentall would agree with most of what I have said above.

[Dr B]

Optical illusions, for instance, resemble a sort of reflex reaction in the brain which we cannot control.

Exactly - it's low-level and based on early grouping / parsing processes. It cannot be penetrated by higher-level thoughts.


Delusions are, by contrast, false beliefs which affect how people deal with the world but not what they actually see or hear.

Exactly, a higher-level phenomenon - but definately not an illusion!!!!!O0

[John Jackson]

Illusions can lead to delusions which is where some confusion may be creeping in. As Dr B says, however, the two are actually different things.

Illusions occur because of the way our brains process information at a low level or automatically. Reading is an example of (learned) automatic processing. The advantage of this is that it does not require conscious effort to complete the task; the disadvantage is that such automatic processing cannot be ‘switched off’ or overridden.

Optical illusions give the best demonstrations of this effect. Look at this picture of two tables. One is long and thin or rectangular, the other is shorter and thicker – almost a square.

http://www.ukskeptics.com/graphics/illusions/table_illusion.gif

The truth is that both table tops are identical! If you print the picture off and use tracing paper to copy one table top then swivel it around and superimpose it on the other one you can prove that they are identical.

The thing is, now that we know that the tops are identical, and have proved it, we still see one as being longer and thinner than the other – the illusion cannot be overridden. We will see the illusion no matter how much we know about it or how many times we look at it.

There are also many other automatic short-cut processes we use (known as heuristics) to process information other than optical. We’re also prone to ‘cognitive illusions’ which arise from how we process other types of information. A simple example is Contiguity (where things occur in close proximity, including in time) leading to the ad hoc or post hoc fallacies. This ‘cognitive assumption’ of cause and effect can lead to people believing that their homeopathic remedy cured their cold or that a new garment worn led to a date with a member of the opposite sex – hence the belief in a ‘lucky shirt/blouse’.

There are many more heuristics which lead to cognitive illusions but they basically work in the same way as optical illusions do. They’re just not so easy to demonstrate.

So illusions of this kind can easily lead to false conclusions, and therefore delusions. Of course, there are other ways that one can reach false conclusions (false beliefs or delusions) which is why delusions are different from illusions. Delusions can be caused by illusions but they are not dependent on them.

Now…

How often do we hear people who believe in ‘weird’ things saying things like: “you’ve got to try it for yourself”, “I saw it with my own eyes”, “I experienced it so I know it was real”, etc.?

What they are not considering, probably because they are unaware of it, is how we can be fooled not only by others, but by ourselves. They’re falling for the fallacy of the infallibility of their own perception.

And illusions are just one example of how we can fool ourselves!

Optical illusions like the one above are a great way of convincing people that what they see is not necessarily what is so. Ironically, because they see it with their own eyes!

But there are also many other forms of cognitive illusion too that are not so easy to demonstrate and unless we know what they are, we fall victim to them in blissful ignorance. They are just as real as the table illusion however. ???

[Dr B]

Now, building on this I would like to state something else. The term 'pseudo-hallucination' is controversial - because hallucinations once considered real can become seen as being unreal (as with the Charles-Bonnet syndrome).

However, it is importarnt for the paranormal in a number of ways. For example, not all skeptical explanations need to recruit notions of hallucination. It could be illusion and even delusion - both of which are independent of hallucination. Then - even if / when one decides it was hallucinatory - there are sub-divisions.

The point to keep in mind is some people hallucinate and know - during the experience - it is unreal. However, some do not - and fully believe their hallucinations to be real. These require different explanations (and are more likely to be invovled in the paranormal).

Also - beware of the Pseudoscientists that say something like "it can't be hallucination because most hallucinations are not treated as real - and this experience clearly was" (the type of argument Fenwick / Parnia and other survivalists trout out all the time). This is not true and what these people are doing is pointing to the literature on 'unreal hallucinations' only (controversially known as pseudo-hallucinations) and claiming that this is true for all hallucinations - not so! Such argumentative style is, at the very least, intellectually misleading.