Transcript Document

Blindsight, Zombies &
Consciousness
Jim Fahey
Department of Cognitive Science
Rensselaer Polytechnic Institute
10/8/2009
Materialism and the Mind
• Standard Materialist View:
• The Mind is NOTHING BUT the Brain and
its workings.
Problems for the Materialist:
• Raw Feels
- pain, love, boredom
• Perceptual States - what you “see” when
you look in the mirror in the morning
• Intentional States
- beliefs, wants, hopes
Problems for the Materialist
(cont.):
• Regarding Raw Feels: How can my feeling
of pain be “nothing but” neurons firing?
• Isn’t it possible for me to coherently
conceive that my neurons might fire in a
“pain-like-pattern” and yet I feel no pain?
Problems for the Materialist
(cont):
• Regarding Perceptual States: How can my
perception of myself in the mirror be
“nothing but” neurons firing?
• Isn’t it possible for me to coherently
conceive that my neurons might fire in a
“seeing-self-in-mirror-way” and yet I have
no perception?
Problems for the Materialist
(cont):
• Regarding Intentional States: How can my
“hope-that-you-have-all-studied-theassigned-readings,” be “nothing but”
neurons firing?
• Isn’t it possible for me to coherently
conceive that my neurons might fire in a
“hope-that-you-have-studied-way” and yet I
have no “hope”?
Problems for the Materialist
(cont): The Zombie Possibility
• More generally, consider the possibility of
Zombies:
• Zombies are like me in that they have brains
and the neurons of those brains:
• Fire in “pain-like-patterns”
• Fire in “seeing-self-in-mirror patterns”
• Fire in “hope-that-you-have-studiedpatterns”
What Zombies Lack
• But while Zombies have brains that are
“neuron-for-neuron” identical to ours,
Zombies:
• FEEL no pain
• SEE nothing
• Have no HOPE
Standard Materialist Responses
to Zombie Arguments
• Reductive Materialist Response:
– It is appropriate to say that “pains, seeings and
hopes” are “nothing but” neurons firing. We
may not understand at present how to “carry
out the reduction” of mental goings-on to
neuronal activity but someday we will.
• Conclusion: Zombies are impossible, since
“same physical stuff/structure” guarantees
“same mental state.”
Standard Materialist Responses
to Zombie Arguments (cont.)
• Eliminative Materialist Response:
– It is NOT appropriate to say that our “folkpsychological” notions of “pains, seeings and
hopes” are “nothing but” neurons firing.
– Conclusion: We DON’T HAVE “pains, seeings
and hopes” in the “folk-psychological” sense
and thus we ARE the ZOMBIES to which the
proponents of folk-psychology refer!
Nicholas Humphrey’s Darwinian
Tale (in his A History of the Mind)
• Nicholas Humphrey offers a sketch of a possible
“history of the mind” that he believes is well
supported by contemporary evolutionary theory.
• The key to Humphrey’s account is the distinction
between the mind as an instrument that reveals
what is happening to me and the mind as an
instrument that reveals what is happening out
there (typically, outside of me).
Sensation
• Humphrey argues that evolutionary theory
supports the view that “early mind” was the
progenitor of what he calls sensation. However,
one might depart from Humphrey and term these
sensations QUALIA.
•
Consider a patch of sunlight falling on the skin
of an amoeba-like animal. The light has
immediate implications for the animal’s own state
of bodily health, and for that reason it gets
represented as a subjective sensation or quale (p.
43).
“Sensations” vs. “Qualia”
What’s the Difference?
In the interest of “full disclosure”:
Humphrey is a functionalist. As such, his
view of “sensations” is ultimately
expressible in terms of (reducible to) states
of a “program up and running.”
“Qualia,” on most accounts, cannot be given
such a functionalist description. Instead,
qualia are most often believed to be
“ontologically irreducible.”
Sensation (cont.)
• The surface of the amoeba undergoes a causal
interaction with the sunlight that falls on it. As a
result of this causal impression, the amoeba
“wiggles” and thus avoids the sun.
• Humphrey believes that at some point in the
evolving history of life on earth, counterparts of
such “impression-wiggle reactions” become fullfledged sensations (?qualia?), sensations that
count as raw feelings of experience of the inner
states of the organisms which are soon followed
by associated behaviors (eg. movements away
from the light).
Perception
•
Later in evolutionary history we find a very
different kind of information process that develops
in “more advanced” animals. Again, speaking of
the amoeba-like animal, Humphrey says,
• “But the light also signifies – as we now know –
an objective physical fact, namely the existence of
the sun. And, although the existence of the sun
might not matter much to an amoeba, there are
other animals and other areas of the physical
world where the ability to take account of what
exists ‘out there beyond my body’ could be of
paramount survival value” (p. 43).
Perception (cont.)
• Humphrey argues that this ability on the
part of animals was not merely a
development of the animal capacity for
sensation but rather it was the development
of an entirely new capacity, that of
perception.
• Question: But is Humphrey’s perception
merely a perception in a picayune sense?
Two Track Model:
Sensation & Perception
Perception
Impression
(eg. light striking the retina)
Sensation
Humphrey’s Arguments for the
Two Track Model:
• Why hold that perception is a new
capacity? Why not hold instead that
perception grows out of and depends on
sensation?
• Humphrey begins by arguing that we can
introspectively separate the “feeling
aspects”or sensations of vision from the
perception aspects. Is this true?
Humphrey’s View Amended
• But Humphrey does not mean to suggest
that “sensation” necessarily involves any
kind of what we would call “reasoning.”
Rather, “sensations” are “feelings” that
baldly occur. It is only much later in the
evolutionary process that “sensations”
become bound up with “reasoning about
what exists” and we get intentional states of
a robust sort.
Milner’s & Goodale’s Model
Pulvinar
Thalamus Track
Action Vision:
Unconscious Perception
Posterior Parietal Cortex
Superior
Colliculus
Dorsal Stream
Primary
Visual Cortex
Retina
?
Ventral Stream
Lateral Geniculate
Nucleus
Memory
Visual Awareness:
Sensation
&
Conscious Perception
Infero
Temporal Cortex
Emotion
(Passions)
Conation
(Willings)
Reason
Amended Two Track Model
Action Vision:
Unconscious Perception
Thalamus
Posterior Parietal Cortex
Dorsal
Primary
Visual Cortex
Ventral
?
?Comparison?
?
Sensation
Conscious
Perception
Amended Two Track Model Plus
Action Vision:
Unconscious Perception
Thalamus
Posterior Parietal Cortex
Dorsal
Primary
Visual Cortex
Ventral
?
Conscious
Perception
?Comparison?
?
Memory
Reason
Sensation
Emotion
Conation
Passions
Willings
The Phenomenon of Blindsight
• If the “two track” model is correct, we
might expect that damage to one of the
tracks that leaves the other intact might
yield kinds of mental states that are
atypical.
• Such is the Phenomenon of Blindsight ...
Blindsight (cont.)
• What is blindsight? Lawrence Weiskrantz,
the originator of the term says in his recent
Consciousness Lost and Found (1997) that
it is “the loss of phenomenal seeing in the
contra-lateral half of the visual field caused
by damage to the primary visual cortex, but
with residual capacity still present.” What
does this come to?
Blindsight (cont.)
• See Humphrey (p. 88)
Blindsight (cont.)
• The following video, Nova: Secrets of the Mind,
features neuropsychologist
V. S. Ramachandran
• Questions you should consider concerning what
follows:
1. What is consciousness? What role does it play
in our mental life?
2. Do the various psychological syndromes
depicted show substance dualism to be false?
Why or why not?
3. On the other extreme, can materialism account
for consciousness?