Holt J. Department of Philosophy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 Canada holtj@cc.umanitoba.ca
Blindsight is a hot topic in philosophy, especially in discussions of consciousness. Here I critically examine various attempts to bring blindsight to bear on debates about qualia -- the raw constituents of consciousness. I argue that blindsight does not unequivocally support any particular theory of qualia. It does, however, vindicate the view that there are qualia, despite arguments -- most notably by Daniel Dennett -- to the contrary.
Kentridge R.W. Dept. of Psychology, Science Laboratories, South
Road, Durham DH1 3LE, U.K Robert.Kentridge@durham.ac.uk
Heywood C.A.
In this introductory paper, we assess the current status of blindsight -- the phenomenon in which patients with damage to their primary visual cortex retain the ability to detect, discriminate and localize visual stimuli presented in areas of their visual field in which they report that they are subjectively blind. Blindsight has garnered a great deal of interest and critical research, in part because of its important implications for the philosophy of mind. We briefly consider why this is so, and then go on to examine three empirical questions which have fuelled challenges to the validity of blindsight as a distinct neuropsychological phenomenon. First, is blindsight simply degraded normal vision? Second, does blindsight depend on undamaged areas of primary visual cortex? Third, does evidence that blindsight patients are aware of moving stimuli undermine the apparent dissociation between access to visual information and visual experience in blindsight? In the course of the review we introduce the four other papers on blindsight in this issue. We conclude that, although patients with primary visual cortex damage may indeed perceive moving stimuli, there is still good evidence for a dissociation between access to information and phenomenal experience which cannot be accounted for in terms of degraded normal vision or undamaged primary visual cortex.
Marzi C.A. Dipartimento di Scienze Neurologiche e della Visione, Universita di Verona, Strada Le Grazie 8, 37134 Verona, Italy marzic@borgoroma.univr.it
It is proposed that there are at least two categories of blindsight. One is present in visually guided behaviour in normals as well as in brain-damaged patients, while the other is present only following cortical lesions. It is also proposed that blindsight is blind because residual visual functions are banned from consciousness either when they are subserved by subcortical centres alone or when they are mediated by cortical areas that have never been exclusively associated with such functions before brain injury.
Morland A.B. Physics Department (Biophysics), Blackett Laboratory, Imperial College, London SW7 2BZ, U.K
Following lesions to the primary visual cortex, some patients maintain visual capacities within areas of the visual field in which they are defined as clinically blind by static field perimetry. Blindsight describes the ability to discriminate visual stimuli in the absence of awareness of the stimuli in such patients. Some patients exhibit blindsight, but others are aware of the stimuli with which they are presented, a response mode that has been referred to as residual vision. The two response modes are of great interest as they are capable of providing us with information concerning the conscious and unconscious processing of visual signals in humans. However, determining consciousness in these patients is a difficult task and relies on the patient assessing and then reporting on his awareness. In this paper, an experiment is described which is capable of demonstrating conscious visual processing of motion under conditions where the observer is not required to assess his level of awareness. In applying this technique to a human hemianope, GY, it is demonstrated that GY has veridical and conscious perception of visual motion presented to his blind hemifield. Although previously reported, this result can be derived without any reference to GY's commentary on his blind field perception.
Pribram K.H. Center for Brain Research and Informational Sciences (BRAINS), Radford University, 423 Russell Hall, Radford, VA 24142, USA kpribram@runet.edu
A report on the meeting on consciousness at King's College London, April 24-25th, 1999
Stark A.
Since you cannot be certain what I mean
By redness, and your experience of violet
Must always be a mystery to me, it seems
We have never really met. Even now,
As we sit face to face, leaning close,
Knees touching, fingertips exploring,
Wide, naked eyes -- we see only images.
You can never be certain what I mean
By despair and, perhaps, you name danger
What I call love. Separated, as we are,
Entombed in our abstractions. Then, you say
'Let's tell the truth' and the terror
of that possibility shakes us awake.
It is only here, before the next thought,
In this electric present, we may connect.
Mosley I. (trans.)
How do birds and fishes feel?
I'll never know!
Here's to the Old Year passing!
Haiku by Basho (1644-94)
The Japanese of the above is:
Uo tori no
Kokoro wa shirazu
Toshiwasure
Mosley I.
I woke from dreaming I was a frog
Into consciousness. A message came to me
(from somewhere in my brain):
Go get your breakfast. I obeyed. Over my newspaper, I read
Of a man called Fred, who killed his children
In search of short relief (perhaps)
From conscious pain.
Oddly confident as to what human consciousness is,
I took my dog, who does not seem to possess the faculty of reason
(though to call him unconscious would seem an abuse of language and
himself,
so busily does he seek out diverse information)
For a walk.
While chasing squirrels
(who seem to me short on that extraordinary quality known as empathy,
something my dog most certainly has, though perhaps he does not know
it)
My dog acquired a tick, whose complex sense of warmth and smell enabled
it
To burrow in his flesh and drink his (tasty?) blood.
I surmised:
The consciousness of ticks is less than that of squirrels
(who gather nuts with an oft-admired foreknowledge)
Lacking, as it does, an awareness of seasons.
I watch the water of the lake, while
The tick feasts on his diet of blood
(and Fred has killed his children)
Reflecting:
How great and many faceted the consciousness of ticks is,
Compared to that of trees
Which, lacking an animal’s complex organs of perception,
Rely on concerted cell reactions
To make their mighty hymns to the Creation —
That shared and primal mystery
Whose solitary and persistent being
Is the inscrutable axiom
Around which all our are worlds are built,
In front of which all posturings save an offering of self
Are laughable and self-deceiving folly.