Introduction
Blindsight is often understood as supporting certain claims concerning the function and
the status of the phenomenal qualities of visual perceptions. In this talk I am going to
present a short argument to show that blindsight could not be understood as evidence for
these claims. The reason is that blindsight cannot be adequately described as a special
case of seeing. Consequently, it is not possible to draw inferences from it concerning the
role of the phenomenal qualities for seeing.
Visual perceptions are supposed to have two sorts of content. First, they have intentional
content which relates them as representations to the external world. The properties
that constitute the intentional content are called representational
or intentional qualities. Second, visual perceptions have phenomenal
content which characterises the subjective experience of them. The phenomenal content
is constituted by introspectively accessible sensational or phenomenal
qualities, so-called visual qualia.
Concerning the role of the phenomenal qualities for seeing particularly the
following two questions are of importance:
(1) The first question is dealing with the causal or functional role
of phenomenal qualities: Under the assumption that seeing is based on cortical
information-processing, the question arises, whether the phenomenal qualities of visual
perceptions have a function with regard to this processing, in the sense that the
intentional content of visual perceptions depends not only on their intentional, but also
on their phenomenal qualities. Is it true, as among other authors Frank Jackson and Steven
Pinker claim, that phenomenal qualities are only epiphenomena, not having any function for
information-processing? (1)
(2) The second question concerns the status of phenomenal qualities: Are the
phenomenal qualities of visual perceptions non-intentional qualities, or do they belong to
a certain type of intentional qualities? In other words, are phenomenal and intentional
contents essentially different, or are the so-called phenomenal contents of visual
perceptions really part of their intentional contents?
In order to come to a decision concerning these two questions, several authors, among
them Peter Carruthers, Daniel Dennett, Colin McGinn, Nicholas Humphrey and Robert
VanGulick, refer to an empirical phenomenon called "blindsight". (2)
Since blindsighted persons receive informations without conscious perception, blindsight
is often understood as supporting the claim that the phenomenal qualities of visual
perceptions do not have a function for the information-processing which gives rise to
their intentional contents, and, consequently, that they are not intentional qualities. In
other words, since blindsight is understood as evidence for the possibility of visual
perceptions of having intentional content, but lacking phenomenal content, blindsight is
interpreted to show that visual qualia are epiphenomenal with regard to the
information-processing of visual perception.
The Phenomenon of Blindsight (3)
Blindsight is a defect which some persons suffer from as a result of a partial damage
of their primary visual cortex. It is typical for this partial cortical blindness that
there is a blind area within the visual field of the persons, who have this sort of brain
damage. Blindsight is remarkable because of the contrast between the lack of declarative
knowledge of the blindsighted persons about the stimuli presented within the blind area,
and the high rate of correct answers to questions concerning those stimuli. On the one
hand, blindsighted persons claim to see nothing within their blind areas: they say that
they do not to have any visual experiences of objects presented within the blind field. In
accordance with this, they are not able to react spontanously to optical stimuli presented
in the blind area, and they also cannot decide on their own, whether something was
presented to them in the blind field, and how the presented objects look like. But on the
other hand, with a frequency significantly above chance level they are able to give
correct answers concerning opticial stimuli present within the blind area, when they are
asked to decide between given alternatives. However, this ability is restricted to a
narrow range of optical stimuli. For example, blindsighted persons can give mostly correct
answers about the presence and absence of points of light, and they are also able to
distinguish simple geometrical forms and patterns. With regard to optical stimuli of this
kind the rate of success of blindsighted persons is between 80 to 90 % of the rate of
success of persons with normal sight. (4)
It is particularly important that blindsighted persons describe themselves as not
seeing anything within their blind fields, and as not having any knowledge about the
objects presented there. Hence, from their perspective they are only guessing, when
they are forced by the insistence of the experimentator to make decisions between given
alternatives. What is amazing about blindsight, is the fact that there is a significant
contrast between the declarative and the procedural knowledge of the blindsighted persons.
Blindsight as a Special Case of Visual Perception
We now come to the question of whether blindsight can be understood as a special case
of visual perception. The reason for this examination is that only under the condition
that blindsight can be regarded as a certain type of seeing, it is possible to draw
conclusions concerning the role of the phenomenal qualities for seeing from the
characteristics of blindsight.
Under the precondition that there is a sufficiently illuminated object x within the
visual field of a physiologically intact person s, the following three points are
candidates for necessary conditions of the application of the term "seeing":
(1) contrafactual condition: The occurrence of a visual perception v is
contrafactually dependent on the presence of an object x within the visual field of a
person s, in such a way that s would have had another visual perception v´ with a
different content than v, if instead of x the different object y would have been presented
to s.
(2) condition of consciousness: The visual perception respectively its
phenomenal qualities must be experienced consciously.
(3) epistemic condition: If a person sees something, then she acquires beliefs
about the presented objects.
ad (1): The contrafactual condition was developed by David Lewis in order to
exclude veridical hallucinations from seeing. This condition is fulfilled in the case of
blindsight, because the answers of blindsighted persons vary in dependence from the
objects which are presented within the blind field. (5)
ad (2): If it is true that blindsight is characterized by the absence of
phenomenal consciousness, then it does not meet the condition of consciousness.
Nonetheless, this condition is not without problems, because it excludes all types
of unconscious visual perception. But psychological research has shown in a number of
different cases that the contents of unconscious visual perceptions of persons with normal
sight actually do have a systematical influence on their behaviour. Therefore, as a
general condition for seeing the condition of consciousness is too narrow and has to be
replaced by a less restrictive condition, which allows both conscious and unconscious
visual perceptions. Consequently, we may regard blindsight as a case of unconscious visual
perception.
ad (3): Verbs of perception are mainly used in two different ways: (1) In the
case of the non-propositional or nominal use, the grammatical object of
the verb consists in a noun, as for example in the sentence "I see Jane".
Generally, this use can be characterized with sentences of the following form: "s
perceives x" ("s" and "x" are placeholders for
persons and for perceived objects). (2) In the case of the propositional use,
the grammatical object of the verb is a proposition, as for example in the sentence
"I see that Jane is blonde". This use can generally be described as follows:
"s perceives that x is F" ("s", "x" and
"F" are placeholders for persons, perceived objects and properties).
In the distinction between non-epistemic and epistemic seeing
Fred Dretske and also G. J. Warnock and Frank Jackson refer to these two different uses of
perceptual verbs. (6) According to Dretske, non-epistemic
seeing is a basic form of visual perception which does not imply the acquisition of
beliefs. Non-epistemic seeing is described by sentences of the general form "s
sees x". It is characteristic of non-epistemic seeing that from "s sees
x" it does not follow that "s sees that x is F". Hence, it is
possible to describe the content of non-epistemic seeing independently from the beliefs of
the perceiver. That means, "s sees x" is an extensional context,
where it is possible to substitute coreferential terms for "x" salva
veritate. In contrast to this, epistemic seeing is characterized by the acquisition of
beliefs. Generally, it can be characterized with sentences of the form "s sees
that x is F". The content of epistemic seeing must be described with reference to
the beliefs of the perceiver. Thus, "s sees that x is F" is an intensional
context, to which the above mentioned principle of substitution cannot be applied.
Blindsighted persons describe themselves as not having any knowledge about the objects
presented within their blind fields. Hence, blindsight does not fulfill the third
condition, if we rely on an internalist conception of belief, since
according to this conception we can ascribe beliefs only under the condition that, for
example, a person has second-order beliefs about her first-order beliefs, (7)
or that she is able to articulate her beliefs verbally, or at least that she does not deny
to have those beliefs we are ascribing to her.
But if instead, following Charles S. Peirce or Gilbert Ryle, we assume the externalist
conception of belief that it is sufficient for the ascription of beliefs, if persons
have certain dispositions of behaviour, then blindsight may meet the epistemic condition. (8)
Although, it is still necessary to define the range of behavioural dispositions in a way
that allows to include the dispositions of persons to react with guessing when
responding to forced-choice-tests. In other words, we also have to take into account
those dispositions of behaviour which persons do not show spontanously, but only after
being forced to make decisions between given alternatives. On the one hand, this
externalist conception of belief is tailor-made for blindsight. But on the other hand, it
is an extremely wide concept of belief, and, thus, not convincing. Therefore, the answer
to the question of whether blindsight meets the epistemic condition, must be negative.
To sum up, from what has been said we can draw the conclusion that blindsight may at
best be regarded as a type of unconscious and non-epistemic seeing. But in this case the
distinction between the intentional and the phenomenal content cannot be applied to
blindsight. This distinction is reserved for epistemic seeing, because non-epistemic
seeing has neither intentional nor phenomenal content. We don´t even have to go so far as
David Armstrong, who claims that only those perceptions have intentional content, which
give rise to beliefs. (9) We only have to follow Dretske´s
view that non-epistemic seeing carries no information. (10)
Therefore, since there are good reasons against ascribing intentional content to
blindsight as a case of non-epistemic seeing, we come to the conclusion that blindsight
cannot give us any evidence about the function of the phenomenal qualities with regard to
the intentional content of visual percep tions.
In addition, it is also doubtful whether blindsight actually meets the conditions for
non-epistemic seeing. According to Dretske, if a person sees a certain object
non-epistemically, then this object is visually differentiated from its immediate
environment by the perceiver. (11) In other words, the
object looks some way to the perceiver. Since blindsighters report that there is nothing
which looks some way to them, it is not without reason to conlude that blindsight even
fails to meet the conditions for non-epistemic seeing.
So we may conclude that blindsight is neither epistemic nor non-epistemic seeing.
Therefore, I think that what we cannot learn from it, is something about the role of
phenomenal qualities for seeing.
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