Blindsight, Zombies & Consciousness

Jim FaheyDepartment of Cognitive ScienceRensselaer Polytechnic Institute

10/4/2007

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 love 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 started working on your final projects,” be “nothing but” neurons firing?

• Isn’t it possible for me to coherently conceive that my neurons might fire in a “hope-against-procrastination” 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-against-procrastination

patterns”

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 “folk-

psychological” 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.

• 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 (p. 43)

Sensation (cont.)

• The surface of the amoeba undergoes a causal interaction with the sunlight that falls on it. As a result of this 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 full-fledged sensations, 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.

Two Track Model:Sensation & Perception

Sensation

Perception

Impression(eg. light striking the retina)

Humphrey’s Arguments for theTwo 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.

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

Retina

SuperiorColliculus

Pulvinar

Visual Awareness:Sensation

&Conscious Perception

InferoTemporal Cortex

PrimaryVisual Cortex

Lateral GeniculateNucleus

Ventral Stream

Thalamus Track

Dorsal Stream

Action Vision:Unconscious Perception

Posterior Parietal Cortex

?

Memory

Emotion(Passions)

Conation(Willings)

Reason

Amended Two Track Model

Sensation

ConsciousPerception

Thalamus

Dorsal

Ventral

?Comparison?

?

PrimaryVisual Cortex

Action Vision:Unconscious Perception

Posterior Parietal Cortex

??

Amended Two Track Model Plus

Sensation

ConsciousPerception

Thalamus

Dorsal

?Comparison?

?

PrimaryVisual Cortex

Action Vision:Unconscious Perception

Posterior Parietal Cortex

??

Memory

EmotionPassions

Reason

ConationWillings

Ventral

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 neuropsychologistV. 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?