A long standing problem in the philosophy of mind concerns the subjective indistinguishability of hallucinations and normal perception. Macbeth’s phenomenal perception of the dagger cannot be differentiated from a normal phenomenal perception of a dagger. So there seems to be no way in which we can tell abnormal perception from normal perception.
(Are hallucinations subjectively indistinguishable from normal perceptions? The answer may be yes and no. I draw on Macbeth’s soliloquy as follows:
Is this a dagger which I see before me,
The handle toward my hand? Come, let me clutch thee.
I have thee not, and yet I see thee still.
Art thou not, fatal vision, sensible
To feeling as to sight? or art thou but
A dagger of the mind, a false creation,
Proceeding from the heat-oppressed brain?
I see thee yet, in form as palpable
As this which now I draw. (II, i)
From this soliloquy, we understand that the hallucinated dagger appears to Macbeth as “palpable” or evident to him as his real dagger. It is in this sense that hallucinations are subjectively indistinguishable from normal perceptions. Yet, we might infer that the total phenomenal experience of a hallucinated dagger is not the same as that of a normal perception- the hallucinated dagger cannot be felt, it can only be seen. This is how Macbeth is able to question his perception of the dagger, questioning if it is real, or if it is a dagger of the mind. In this example, what Macbeth experiences would be a confusion in which it is difficult to know just what is real and what is not.)
There is a similar problem in the case of delusions. It is hard to tell that one has a false belief. I believe that John is out to get me, but John is not out to get me. How is my erroneous paranoid belief different from any other normal case of belief?
In response to these problems, disjunctivist theories of perception hold that there are genuine differences between abnormal perceptions and normal perceptions, despite the appearance of there being no difference. I defend a kind of epistemological disjunctivism about perception.
In this essay, I argue that the main difference between abnormal perception and normal perception is the mind-dependence of abnormal perception. Perception is mind-dependent in that either the existence or the character of the objects of perception depends upon the mind.
Perception would be mind-independent if it were not mind-dependent. That is, perception is mind-independent whenever the existence of the character of the objects of perception does not depend upon the mind.
In normal perception, there is a definite extent to which there is mind-independence of the objects of perception. Without my perceiving the object, the object would still exist. By contrast, the hallucinated object cannot exist without my perceiving it.
In the case of delusion, the mind is needed to cause the distortion of the perception. By contrast, the normal perceiver’s experience is mind-independent. Although it is necessary for there to be an act of perception in order for the object to appear, it is not necessary for there to be a mind in order for the object to appear as such-and-such.
The structure of my essay is as follows. I first give an example of a hallucination, and then an example of a delusion. I then use a simple act-object model of perception to explain the mind-dependent nature of the objects and acts of psychotic experience.
Hallucinations typically involve the perception of things that do not exist, while delusions typically involve distorted perceptions of things and false beliefs about things that do exist. The mind-dependence of hallucinations is therefore more prominent than the mind-dependence of delusions.
Psychosis is an experience whereby an individual has hallucinations, delusions, or abnormal behavior as a result of abnormal thinking and perception. The objects of psychotic experience are mind-dependent, in the sense that
a) the objects of hallucinations depend upon the mind for their existence
b) the objects of delusions depend upon the mind for the distortion of perception.
If we can explain the essential difference between abnormal and normal perception, then the problem of subjective indistinguishability becomes less worrying. We are at least able to define an essential condition of hallucinations: X is a hallucination whenever X is an entirely mind-dependent object of perception.
As such, if Macbeth sees a dagger, then we know that the dagger is a hallucination if Macbeth’s experience of the dagger is an entirely mind-dependent experience. What Macbeth sees is not a real dagger. Although we are unable to phenomenally distinguish between hallucinations and normal perception, it is possible to at least distinguish them conceptually.
It is more difficult in the case of delusions, because if Y is a somewhat mind-dependent object of perception, the condition is insufficient for Y to be a delusion. Normal perceptions are, to some degree, mind-dependent. Yet we cannot add that Y is a distortion of perception, since that is simply to re-word the problem. Setting out the conditions for delusions is a difficult problem indeed.
Perhaps the difference between a delusion and a normal perception or belief lies in discerning between different senses of mind-dependence. A delusion is mind-dependent in that the mind causes distortion, while normal perception is mind-dependent in the usual way of the objects of perception being conceived through concepts of the mind.
Case of hallucination: the yellow wallpaper
Here is an example of a hallucination that depends upon the mind for its existence.
In the story, The Yellow Wallpaper, by Charlotte Perkins Gilman, the protagonist at one point believes that she sees a woman in the wallpaper. The woman hides in the wallpaper, and comes out of the wallpaper, creeping and hiding.
How does the protagonist make out a woman hiding from the shapes that she sees in the wallpaper? The protagonist stares at the wallpaper and at the patterns in the wallpaper. There is a sense in which something is odd about the wallpaper, and she wants to find out what exactly is odd about it. The protagonist is having a premonition.
The premonition is required for there to be a hallucinatory experience. Since the experience of having a premonition needs to be supported by some evidence, the protagonist finds a woman in the wallpaper as an explanation for having the premonition. The creeping woman fits into her overall experience. Only if it is a creeping woman does her observation about the wallpaper make sense.
The mind is required for there to be a premonition. Premonition is not simply a thought that occurs to one, but an emotion or feeling that may include a heavy and fuzzy feeling of anxiety or nausea. For the protagonist in the story, the feeling of premonition collided with the observation of various shapes on wallpaper in a complex way to create the image of a woman creeping.
Case of delusion: an epiphanic moment
Here is an example of a delusion that depends upon the mind for the distortion of perception.
Suppose that two individuals are looking at a small, blue chair that is next to a larger, green chair. The normal individual perceives these as pieces of furniture in a room. The psychotic individual has an epiphany. He perceives these objects as reflecting the relationship between mother and child. The larger green chair stands for the mother, and the small, blue chair stands for the child. The green color of the chair represents contamination of thought and deed, while the blue color of the chair represents purity of thought and deed. Further, the psychotic individual sees himself as being represented by the blue chair, and his mother as being represented by the green chair.
How does the individual with psychosis come to have this false belief? The psychotic individual projects his thoughts about the relationship between himself and his mother onto the pieces of furniture. The pieces of furniture by themselves do not say anything about the relationship between particular human beings. What caused the epiphanic nature of the experience was some kind of connection made between the individual’s background of ideas and thoughts and the appearance of something.
The psychotic individual had made a parallel between his thought and what he saw in the world. The appearance of two chairs had the same underlying pattern as the relationship between two human beings. The large size of one chair suggested the notion of an adult, while the small size of the other chair suggested the notion of a child. The appearance of two chairs and the buried thought in his mind coincided to form the epiphanic moment.
Both the appearance of the two chairs and the buried thought-the causal elements of the psychotic experience- are mind-dependent. The appearance of the two chairs was not passive reception of data, but the active organization of data into objects that became signifiers for something else. The buried thought forms part of the background of ideas and thoughts. As the mind saw the two chairs, it linked together the buried thought with the appearance of the two chairs, causing the ‘eureka’ moment.
I have chosen the epiphanic moment as an example not because it is unique only to delusions and not to hallucinations. A hallucination can be accompanied by the feeling of epiphany. In this case, though, the epiphanic moment illustrates false belief.
The act-object model of perception in psychotic experience
In a simple act-object model of perception, the act of perception is the looking at an object, while the object of perception is what appears to the perceiver. If I am looking at a brown table, my looking at the table is an act, while the appearance of the table is the object. I shall use this act-object model of perception as a starting point to think about the nature of psychotic experience.
Initially, the objects and acts of perception in psychotic experience appear to be mind-independent. This is the pre-theoretical view of perception. If I see a tree, it is because there is a tree. Data that there is a tree is given to me, and the data informs me that a tree exists in front of me.
However, if the objects of perception in psychotic experience were mind-independent, then these objects would exist in the external world. Since many of these objects, for example, hallucinated voices, do not exist in the external world, so the objects of perception in psychotic experience are not mind-independent.
And if the acts of perception in psychotic experience were mind-independent, then the acts of perception would be thoroughly passive in character. Perception would be like a sponge soaking up water. If the acts of perception were thoroughly passive, though, it would be difficult to explain delusional phenomena like false beliefs and false epiphanic moments. Hence, there is explanatory value in stating that the acts of perception in psychotic experience are mind-dependent.
I use an act-object model of perception to analyze psychotic experience, because, it seems that the difference between psychotic and normal experience lies in perception, and it seems that the act-object model is a useful way of thinking about perception. If the objects and acts of perception in psychotic experience are mind-dependent, the question arises as to how they are mind-dependent.
The mind-dependent nature of the objects of perception in psychotic experience
The objects of perception in psychotic experience are mind-dependent, even if they seem to be mind-independent.
In psychotic experience, the objects of experience seem to be given. There seems to be passive reception of the objects of experience. For instance, it would seem to Macbeth that the dagger appears before him without his actively seeking it. If the objects of psychotic experience are given, then the objects of psychotic experience are said to be mind-independent.
However, this appearance of passive reception of objects of psychotic experience is obviously untrue. The experience of a hallucination cannot be mere passive reception. If an individual with schizophrenia hears voices, and everyone else hears silence, and if the environmental conditions are the same, then it is likely that the mind-independent external world did not cause the change in what is perceived. Rather the change was caused by a difference in the individuals’ faculties of perception or a difference in the particular acts of perception, or both.
Likewise, the experience of a delusion is not passive reception. If an individual with psychosis sees a string of numbers as hiding a coded message from a well-known celebrity, and if everyone else sees the same string of numbers as a random string of numbers, then all other things being equal, it is likely that the change is what is perceived comes from a difference in the individuals’ faculties of perception or a difference in the particular acts of perception, or both.
The faculties of perception are powers to perceive. For example, the faculty of vision gives one the power to see things. The faculty of vision can affect what is seen, so a particular individual’s faculty may not be able to distinguish between red and green. Here, the defect is in the faculties and not in the acts of perception.
By contrast, an act of perception is the doing of perception. For example, looking is an act of perception. The act of perception differs when the perceiver looks at an object in one way rather than in another way, so that for instance, for one individual, all the objects remain in the background, but for another individual, some objects are highlighted, as it were, to the mind. The act of looking confers meaning when attention is drawn to particular objects and not to others.
Prima facie, it might seem as though the matter is a difference in interpretation- one interpretation being the coded message from a well-known celebrity, and another interpretation being a random string of numbers. Just as we can interpret a visual illusion to be either a vase or two persons’ side profiles, we can interpret any phenomena to be either such-and-such or thus-and-so.
If the difference were one of interpretation, then there is still a large sense in which the objects of psychotic experience are mind-independent. Just like a traditional view of how data is mind-independent and theory is mind-dependent, the objects of experience- whether psychotic or not- are mind-independent and the interpretations of the objects are mind-dependent.
The problem with the view that a delusion is simply a different interpretation of the same phenomena, is that it neglects the actual difference in perception between the normal individual and the individual with psychosis. For the individual with psychosis, various items appear to pop-out in experience. This does not happen for the normal perceiver. The phenomenon of popping-out is not a way of interpreting data, but a way of looking at and selecting the items of experience.
“Popping-out” in basic perceptual reality can be explained in terms of attention. The appearance of “popping-out” is not caused by the things themselves, but is caused by the mind’s spotlight of attention focusing onto particular things but not onto others. So, while a normal perceiver would scan around a room and not notice anything special, a person with psychosis would zoom in on two particular chairs, feel an epiphanic moment, and see a special significance. What happens when the two chairs are “popping-out” in his experience is his mind somehow focusing attention on the two chairs.
As such, the difference between a delusion and a normal perception is not simply a difference in interpretation. The objects of experience cannot be mind-independent in the simplistic manner following the traditional view. So, one obvious sense in which psychotic experience could be mind-independent seems mistaken.
To say that psychotic experience is mind-dependent is to say that there would be no psychotic experience if there were no mind. In other words, psychotic experience is a mental phenomenon. This applies to both hallucinations and delusions. In both hallucinations and delusions, there appear to be mind-independent objects which are either entirely mind-dependent, in the case of hallucinations, or somewhat mind-independent, in the case of delusions.
This mind-dependence is a striking difference between cases of abnormal perception and normal perception. If so, the subjective indistinguishability of hallucinations and normal perceptions seems less worrying. The mind-dependence of delusion also highlights the difference between belief and distorted belief.
The argument from hallucinations is characterized as follows:
(1) We cannot phenomenally distinguish between hallucinations and normal perceptions.
(2) Both hallucinations and normal perceptions seem to involve mind-independent objects.
(3) Hallucinations do not involve mind-independent objects.
(4) We cannot know whether normal perception really involves mind-independent objects.
If we conceptually distinguish between hallucinations and normal perceptions as I have done in this essay, this is to assert that what makes hallucinations different from normal perceptions is precisely that one involves mind-independent objects, but the other involves mind-dependent objects. The argument from hallucination could be re-written as:
(1) If we cannot phenomenally distinguish between hallucinations and normal perceptions, then there is no difference between the objects of hallucinations and the objects of normal perceptions.
(2) The objects of hallucinations do not exist.
(3) Hence, the objects of normal perceptions do not exist.
However, there is a difference between the two, namely, that one is mind-dependent and that the other is mind-
independent. We can contrast hallucinations and normal perceptions in the following manner:
In normal perception-
What I see is what is the case.
I see a blue pen.
There is a blue pen.
What I see is not the case.
I see a blue pen.
There is no blue pen.
Further, visual illusions like the Müller-Lyer illusion tell us that what we phenomenally experience may not be the best indicator of what is true. Even if we are unable to phenomenally distinguish between hallucinations and normal perceptions, it does not tell us that there is no genuine difference, possibly epistemological, between hallucinations and normal perceptions.
We can extend the analysis to include delusion.
What I see is not the case.
I see a blue pen hiding a message from God.
There is a blue pen, but no message from God.
The breakdown of delusion shows that delusion is very different from what a normal perception might be. In this essay, I have tried to show how abnormal perceptions like hallucinations and delusions are different from normal perceptions. I hope that this in some way creates understanding that the argument from hallucinations may not be a problem at all. Secondly, I hope to have made some headway into the problem of delusions in general.
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Schiller, L and Bennett, A. 1994. The Quiet Room. USA: Warner Books