Chapter 18: Damaged Brains
- Brain damage-caused deficits one important source of evidence
about the neural correlates of consciousness and other "mental"
- E.g., loss of impulse control and planning ability in patients
with damages frontal & prefrontal lobes supports the hypothesis
that that choice and volition are localized in these areas. (see chapter 9)
- "What is it like?" questions (257) associated with various
- "What is it like not to notice you don't notice half the world?"
- "What is it like to be blind but believe that you can see, or
paralyzed but convinced that you can move?"
- "What is it like to be suspended in the present moment with no
- Two types
- retrograde: loss of long term memory that stretches back into
- anterograde: loss of the ability to store new long-term memories
- Korakoff's syndrome & Jimmie G.
- an anterograde amnesia caused by alcoholism (generally)
- accompanied by retrograde amnesia (naturally) dating back to
the onset of the syndrome (& before?)
- Oliver Sacks described J.G.'s amnesia as "a bottomless
memory-hole that would engulf the whole world." (1985: 34)
- "episodic memory (that is memory for the events of one's life)
remains perfectly good for the far past, before the blank period, but
no new episodic memories are laid down. (258)
- many remaining memory-like abilities (258-9)
- to be classically conditioned: e.g., to blink at a sound
which has been associate in past trials with a blast of air to the eye
- "to associate smells with lunchtime"
- "to respond to a given visitor with pleasure, even if they
claim never to have seen that person before"
- retain such skills as driving & typing
- can even acquire new skills unawares, as it were -- like.
learning to play the piano without "remembering" ever having a lesson
- SB's analysis (259-60)
- surely, amnesiacs are conscious: "They are awake, responsive,
able to converse, laugh and show emotion."
- "But who is conscious?" That's the question.
- "Without the capacity to lay down new memories, their self is
a person trapped in the past, unrelated to the events and people of the
- "They have lost the interaction between current and stored
information that, according to Weiskrantz (1997), makes possible the
"commentary" that underwrites conscious experience."
- "Some amnesiacs repeatedly exclaim, 'I have just woken up!'
or 'I have just become conscious for the first time!'"
- Sacks: "If a man has lost a leg or an eye, he knows he has
lost a leg or an eye; but if he has lost a self -- himself -- he cannot
know it, because he is no longer there to know it." (1985: 34)
- Still, "a man does not consist of memory alone. He has
feeling, will, sensibilities, and moral being."
- Anosagnosia: Paralysis neglect,
- e.g., "a patient who is paralyzed down his left side
may say that he can move perfectly well if he wants to"
- caused by certain kinds of right-brain damage
- Anton's syndrome: blindness neglect
- "Patients are blind and yet insist that they can see."
- "When they bump into things, as they frequently must, they
confabulate, inventing an ingenious range of excuses rather than
concluding that they are blind." (260)
- Hemifield or unilateral neglect:
- the syndrome
- characterizations & explanations (262-3)
- "Hemifield neglect can partly be explained as a deficit of
attention, in that patients simply do not attend to, or have their
attention drawn to, the left-hand side of the world"
- "clearly the unattended side is not completely blanked out"
- "emotional stimuli shown in the neglected field can
influence attention and stimuli that are not consciously seen can prime
- "In one experiment patients were shown two pictures of a
house, identical except that one had flames pouring from a window on
the left-hand side. While insisting that the houses were
identical, patients still said that they would prefer to live in the
[the bottom house in this instance (Fig. 18.2), i.e., the] one that is
not on fire."
- Patient D.B. (263)
- had part V1 of his left visual brain removed, leaving him blind
on the right side "since input from the right visual field goes to the
left brain, and vice versa"
- "If he looks straight ahead and an object is placed on his
blind side, he cannot see it" -- or so he says
- Weiskrantz's blindsight experiment (see Fig. 18.3)
- show a circle with stripes in his normal field he says he can
see it and easily tells whether the stripes are vertical or horizontal
- shown the same circles in his "blind" field he denies he sees
anything yet his forced "guesses" are 90-95% correct.
- Related phenomena that have been observed
- "deaf hearing"
- "numbsense" (Weiskrantz 1997)
- Interpretations, etc.
- The obvious interpretation: "the blindseer has vision
without consciousness" (265)
- showing "that consciousness is something separate from the
ordinary processes of vision"
- "that qualia exist and functionalism is wrong"
- that there is a "finishing line" and a "Cartesian theater"
- the "stray light" hypothesis disconfirmed
- Presumptive physiological basis: "There are something like 10
separate, parallel pathways from the eye to different parts of the
brain. About 85 percent of cells take the major route through the
lateral geniculate to primary visual cortex, gut the rest go via the
superior callicus to various other cortical and subcortical
areas. ... The evidence suggests that true blindsight
occurs when V1 is destroyed and these other pathways remain intact."
- Weiskrantz: "The subjects seemed to be able to respond to the
stimuli that would normally generate the philosophers' favourite
species of 'qualia,' namely colours, but in the absence of the very
qualia themselves!" (1997: 23)
- Dennett's Challenge: superblindsight
- blindsight subjects "have to be prompted to guess and are given
no immediate feedback on their success" (266)
- suppose instead we train the subject "giving him feedback on
his guesses until he comes to realize that he has a useful
ability. Next he is trained, again by giving feedback, to guess
on his own, without being prompted. After this training he should
spontaneously be able to talk about, act upon and use the information
from his blind field just as well as from his seeing field." (266)
- at issue: "if the superblindseer could really use the
information about a stimulus in the blind field in this way, would that
mean he was necessarily conscious of it?"
- Cognitivism (e.g., Dennett) say "yes":
- functional equivalence => phenomenal (i.e., conscious or
- full-functional zombies are impossible
- anticognitivists say "no"
- functional equivalence =/> phenomenal equivalence
- full-functional zombies are possible
- pertinent fact: actual
blindsight is not
- "blindseers generally cannot recognize forms or identify
- "They cannot (or at least do not) use their blindsight in
- some blindseers are aware of fast-moving, high-contrast
phenomena in their blind field, in effect, "seeing movement without
seeing the thing that is moving" or "not bound to a moving object" (268)
- "the intact field seems biased towards object
identification, and the Blindsight field towards stimulus detection"
- sensory substitution: using one sensory modality (e.g., touch
or hearing) to process information from another (e.g., vision): "with
practice it seems [to them] to become more and more like seeing"
suggesting "consciousness comes along with increasing function rather
than being something separate from it" (269)
- Block's analysis (1995)
- distinguish between access consciousness (Consciousness) and
phenomenal consciousness (Consciousness) (SB: 269)
- A = "the availability of information for use in reasoning,
speech and action"
- P = "experience or 'what it is like' to be in a given
- Block argues that stimuli in blindsight are unconscious in
- "For Block the superblindsight case is indeed a partial
zombie who has A-consciousness (because he can talk about stimuli in
his blind field) but no P-consciousness (because he has no visual
- Dennett disagrees: "blindsight does not support the concept
of a zombie, it undermines it" (270)
- Weiskrantz's view (tending to support Dennett)
- W's hypothesis: blindseers lack the "commentary stage":
a kind of HOT theory
- this is exactly what's added in Dennett's superblindseers
- Dennett's superblindseers would be expected to regain
consciousness upon having their "commentary stage" thus restored, then,
on W's hypothesis.