IMPORTANCIA, ADMINISTRACIÓN Y MEDICIÓN DEL RIESGO DE MERCADO

There is a much overlooked form of the argument from hallucination concerned not with types of experience but with the token experience involved in a token perception: it aims to show that this token experience could have occurred in the absence of the object perceived and so cannot be sufficient to

ground direct demonstrative reference to the object perceived. Establishing this conclusion, of course, is establishing the falsity of Sartre’s conception of perceptual experience as apprehension of mind-independent reality. The argument is based on the generative theory: if a token experience is caused by the excitation of the neural system, then even if there is no causal or other law connecting the two events qua events of certain types, there is still the token relation of causation between the events considered as tokens. Given the generative theory, then, the token neural stimulation is alone sufficient for the occurrence of the token experience involved in a perception, and since the object seen is no part of the token neural stimulation, the token experience could have occurred in the absence of the object seen. If the token experience is independent of the object in this way, if it could have occurred as an hallucination, the argument runs, then it cannot ground the perceiver’s ability to demonstratively identify the object (see Malebranche 1997, 10-11; Valberg 1992, ch. 1).

More formally, this argument adds just one premise to the generative theory to reach its conclusion. This second premise, which I shall refer to as ‘the causal claim’, states that a token event could counterfactually have been

caused by an event other than the event which in fact caused it. If ei caused

0 2, according to this premise, ez could have occurred without ei so long as

some other event occurred in the place of e^ and that other event caused Oz. Although, when I see a table, certain disturbances in my visual cortex are traceable along an actual causal chain back to the event of light bouncing off the table, the same token disturbances could counterfactually have been brought about even if the table had never existed - perhaps by the direct stimulation of my retina by electrodes, or by the agency of God.

The generative theory and the causal claim form the premises of what I shall refer to as ‘the casual argument’: a token perceptual experience is generated by a token neural stim ulation; that token neural stim ulation could counterfactually have been brought about in the absence of the object

actually perceived; therefore a token perceptual experience could counterfactually have been brought about in the absence of the object actually perceived. Strong disjunctivists such as Sartre are immune to this argument since they reject the generative theory. But weak disjunctivists accept the generative theory, and so must do one of three things: deny the causal claim; deny that the conclusion follows from the conjunction of the generative theory and the causal claim; or accept the conclusion but deny that it presents any threat to weak disjunctivism.

In order to reject the causal claim, weak disjunctivists must claim that there is a class of token events such that no member of the class could have occurred in the absence of its actual causal aetiology and this class includes token perceptual experiences. In order to make this claim, it is not sufficient to point out that a perception - like a footprint or a photograph - must by definition be caused in a certain way (e.g. Pitcher 1971, 50-7), since this obviously allows that the same token experience could occur as a perception or as an hallucination depending on its causal aetiology, which is precisely what all disjunctivists reject.

What is required to deny that any token experience could have occurred in the absence of its actual causal aetiology is a form of causal essentialism according to which there is a class of token events such that it is essential to each member of the class being the event it is that it has as an immediate cause the token event that in fact caused it. So long as token event e2 is in

this class, it is simply not true to claim that 0 2 could have occurred in the

absence of its actual cause ei. Since e2 was caused by ei, e2 is essentially

caused by ei, so unless ei had occurred, 0 2 could not have occurred. If this

causal essentialism is to protect weak disjunctivism from the causal argument, the class of token events that have their causes essentially must include token perceptual experiences and all the token events involved in linking token experiences to perceived objects in perception. If any event in the causal chain reaching from a token perceptual experience of a table back to

the table is outside the class of events that have their causes essentially, then bringing about that event in the absence of the table will bring about the rest of the actual causal chain including the resulting experience. Given suitable membership of the class of events that have their causes essentially, then, this causal essentialism would allow weak disjunctivism to resist the causal argument: an experience actually caused by a chain of events leading back to light bouncing off a table could not have been brought about in any other way.

The problem with this causal essentialism, though, is that unless a sufficient motivation can be provided for embracing it an opponent can simply deny it, and it seems that there is no available motivation for it. The motivation, it seems, must be based on an adaptation of Fine’s (1994) conception of the relation between essence and definition, so that the properties mentioned in or entailed by the definition of a token event are essential to that token event. The cause of a token event will be essential to it, then, if it is mentioned in or entailed by the identity and individuation criteria that single out that token event in the actual world. Since the cause of a token event is not entailed by any definition of that event except one that explicitly mentions the cause, this form of causal essentialism must embrace the view that there is a class of token events that are identified and individuated (at least partly) by reference to their causes. And herein lies the problem: since the cause of a token event is another token event, as Quine (1985, 166) has pointed out, any definition of token events in terms of their causes already quantifies over token events and hence presupposes a prior individuation criterion for the token events over which it quantifies. Once this prior criterion is in place, there is no room for a second, causal criterion for any token events. It is this problem of circularity that underlies Davidson’s rejection of his former view that events are to be identified and individuated by reference to their causal roles (see Davidson 1969, 231; 1985, 175).

It is impossible, therefore, to define a token event by reference to its cause, and in the absence of such a definition it is difficult to see how one could

motivate the claim that the events involved in perception have their causes essentially. Weak disjunctivists cannot, it seems, deny the causal claim by claiming that there is a class of token events such that no member of the class could have occurred in the absence of its actual causal aetiology. This failure to deny the causal claim leaves the weak disjunctivist with two options: deny that the conclusion of the causal argument follows from its premises, or deny that the conclusion is incompatible with weak disjunctivism.

In order to claim that the conclusion of this argument does not in fact follow from the conjunction of the generative theory and the causal claim, weak disjunctivists might exploit the argument's presumption that when I see an object in ordinary ambient light, for example, the object I see is necessarily the one that last reflected or significantly refracted the light that entered my eyes, or in the case of silhouettes and back-lit objects the object that blocked light otherwise heading for my eyes, or in the absence of reflection, significant refraction, or blocking, the one that emitted light directly into my eyes. The argument presumes, that is, that an experience brought about by an object transmitting light into my eyes or blocking light otherwise heading for my eyes

is thereby a perception of that object.® The weak disjunctivist might try to deny

this assumption, and thereby maintain both the generative theory and the causal claim while resisting the conclusion of the argument, by construing perception as a relation between perceiver and perceived that is distinct from but brought about by the causal relation. Optical stimulation, to take seeing as an example, delivers information to the visual system, on the basis of which the seer’s mind directs its attention to some part of the immediate environment and the ensuing experience consists in a direct relation to the part of the environment attention is directed towards. The experience is brought about by the causal relation between an object and the seer’s eyes but is not thereby a perception of that object; rather, the experience is a perception of that object in virtue of the experience itself being a separate relation between seer and object. This form of weak disjunctivism, then, agrees that a perceptual visual experience results from the excitation of the

Visual cortex but denies that the same experience could occur in the absence of its object (see Coates 1998, 20-5).

In order to avoid collapsing into intentionalism, of course, this form of weak disjunctivism must deny that experience consists in having information encoded in a brain state. Instead the information encoded in the brain state must be taken to determine the direction and range of some sort of mental glance and the experience consists in this glance. The information must determine which object in the perceiver’s environment is to be glanced at, however, and herein lies the problem with this conception of perception. In the case of visual perception, the object at the centre of visual attention is always the object transmitting light onto the foveal regions of the retinas, or blocking light otherwise heading there. Any theory of vision must allow for this fact. The form of weak disjunctivism under consideration, then, must claim that in such cases the information encoded in the brain state uniquely specifies the object transmitting light onto the foveal regions. Since there may be two objects equidistant from the perceiver and alike in all respects except spatial location, the information encoded in the brain state can single out which object to glance at only by (egocentric or objective) spatial co-ordinates.

But this view, that seeing a part of the world consists in a relation independent of any causal relation but determined by spatial co-ordinates encoded in a brain state, is clearly falsified by experiments involving displacing glasses. Such glasses alter the angle at which light enters the eyes, so that (for example) light deflected from a table to my left will enter my eyes at the angle it would normally have entered at had the table been straight in front of me. The form of weak disjunctivism that we are considering predicts that in such a case (wearing the glasses for the first time, so that my brain has not had time to adjust), I will cast my mental gaze ahead of me toward the location indicated by the message received from my retinas and see whatever is there (not the table, which is to my left). In such a situation, however, I do in fact

see and can describe the table, but I mislocate it in space - it is my behaviour that misfires, not my perception (see Gregory 1998, 138-43).

Only (egocentric or objective) spatial co-ordinates can be relied upon to single out a specific object, then, but experiments involving displacing glasses have shown that visual perception does not consist in an experience directed toward an object in virtue of a set of spatial co-ordinates. Visual perception, therefore, does not consist in a mental glance directed toward an object specified by information encoded in a brain state. This form of weak disjunctivism, therefore, is false. In order to guarantee that an experience brought about by an object transmitting light onto the foveal regions of my retinas, or blocking light otherwise heading for the foveal regions of my retinas, is a perception of that object, we must agree with the presumption of the causal argument that the experience is a perception of that object in virtue of that causal relation between the object and the brain. Given this presumption, the causal argument is valid, so the weak disjunctivist is left with the option of denying that the causal argument presents any significant threat.

Weak disjunctivists might argue that the conclusion of the causal argument is incompatible with weak disjunctivism only if it is understood in terms of a conception of token experiences, of experiences as particulars or datable occurrences, that includes reference to experiential type. On a conception of token experiences inspired by Kim's (1973) conception of a token event as the exemplification of a property by an object at a time, a token experience is the having of an experience of a certain type by a particular experiencer at a particular time. If this is what a token experience is, then having the same token experience involves having an experience of the same type, so if an actual token perceptual experience could counterfactually occur in the absence of the seen object, then an experience of the same type as occurs in a perception could occur as an hallucination, which is precisely the ‘single common element’ or ‘highest common factor’ view of the relation between perception and hallucination that is denied by all forms of disjunctivism. But

this just shows that the Kimesque conception of token experiences is incompatible with weak disjunctivism, given the causal claim and the presumption of the causal argument. Weak disjunctivists need not be troubled by this, since they can deny that identity and individuation criteria for token experiences make reference to experiential type. They may, for example, appeal to conception of token experiences based on Davidson’s (1985, 175) conception of token events as unstructured particulars picked out by their spatiotemporal co-ordinates. On this conception, the same token experience can occur actually as a perceptual experience and counterfactually as an hallucinatory experience: all that matters for sameness of token experience is sameness of spatiotemporal co-ordinates. So the fact that the token perceptual experience could counterfactually have occurred in the absence of the seen object is no threat to weak disjunctivism: had it so occurred, it would not have been a perceptual experience affording direct demonstrative reference to a part of the world, but instead the same token experience would have been an experience of the hallucinatory type.

This response to the conclusion of the causal argument on behalf of weak disjunctivism is, so far as it goes, entirely correct. The conclusion of the causal argument is strictly incompatible with weak disjunctivism only given a Kimesque conception of token experiences, a conception that weak disjunctivists can reject. But the response does not go far enough, because the threat posed to weak disjunctivism by the causal argument need not be construed as the establishing of a conclusion incompatible with weak disjunctivism. The causal argument might rather be construed as highlighting an explanatory deficiency of weak disjunctivism. If a token neural stimulation, whose spatiotemporal co-ordinates are all within the subject’s body, causes a token experience which might occur as either perceptual or hallucinatory, then what explains whether the experience is perceptual or hallucinatory? What explains the difference in type between the actual perceptual experience and the counterfactual hallucinatory experience when both are claimed to have been generated by the same token neural stimulation?

We have seen in discussing the possibility of causal essentialism that it would be simply arbitrary to deny that the same token neural stimulation could occur with a different causal aetiology, so if there is any possible world in which the token neural stimulation involved in my actual perception of the London Eye generates an hallucinatory experience, then there is no reason to rule out there being a possible world like the actual world in all respects (including causal aetiology of the neural stimulation) except that on that occasion I have an hallucinatory rather than a perceptual experience. I am now perceiving, that is, but if it is possible for my actual token neural stimulation to cause an hallucination, then it is possible for my actual token neural stimulation with its actual causal aetiology to cause an hallucination, so there is no reason why I am not hallucinating.

In appealing to the claim that the same token neural stimulation causes the same token experience but sameness of token experience is independent of whether the experience falls under the perceptual or hallucinatory type, then, weak disjunctivism is hoist by its own petard: it rules out the possibility of any general account of why people have perceptual and hallucinatory experiences when they do. Providing an account of the relation between perceptual and hallucinatory experience that explains why one has the experiences one has is the key aim of theories of experience; any theory that rules out such an account is missing the main course.

So the view that a perceptual experience involves the perceived object in such a way as to ground direct demonstrative reference to it cannot be satisfactorily defended against the causal argument by weak disjunctivism. It allows that the token neural excitation that actually generated a perceptual experience might counterfactually have been the same in all respects but have generated an hallucinatory experience. If the token event that generated a token perceptual experience might just as well have generated an

hallucinatory one, we are left without any possible explanation of why it generated a perceptual as opposed to hallucinatory experience.

What is required to block the causal argument satisfactorily is not the type- externalism of weak disjunctivism, but a token-externalist conception of