東京大学学際科学科 2013年度 総合情報学特論III 意識の科学的研究 - 盲視を起点に 6月26日(水) 3-4限 13:00-16:20, 駒場キャンパス15号館1階104講義室 吉田 正俊 (自然科学研究機構・生理学研究所・認知行動発達研究部門 助教)

1. 東京大学学際科学科 2013年度 総合情報学特論III
意識の科学的研究 - 盲視を起点に
6月26日(水) 3-4限 13:00-16:20, 駒場キャンパス15号館1階104講義室
吉田 正俊 (自然科学研究機構・生理学研究所・認知行動発達研究部門 助教)
要旨 Part 1:
• The idea of two visual systems (cortical vs. subcortical) was confirmed in various animals.
• The dorsal and ventral visual pathways may have different roles on vision for action and vision for
perception, respectively.
• Feeling-of-something-happening in blindsight may be mediated by the dorsal pathway for saliency.
要旨 Part 2:
• Neural correlates of awareness can be studied using bistable percepts.
• Vision is not passive. Brain is predictive.
• Sensorimotor contingency explains our perception to some extent.
• The dorsal pathway for sensorimotor contingency and the ventral pathway for internal model?
• Current scientific study of consciousness is the study of philosophical zombie.
• Neurophenomenology tries to establish a first-person methodology but it is not successful yet.
PART 1
0. What is consciousness?
-- Let’s start from examples
• Salient visual stimuli can disappear.
• We are not conscious of all of the signals on the
retina.
1. What is Blindsight (盲視)?
• Q: What is blindsight?
• A: “The visually evoked voluntary responses of
patients with striate cortical destruction that are
demonstrated despite a phenomenal blindness”
1
• Phenomenal consciousness can be dissociated
from visual information processing.
2. Two visual systems:
Cortical vs. Subcortical
2-1. Two visual systems in monkeys
• Bilateral lesion in V1 - first report of blindsight in
monkey
2
• Retained: visually guided reaching and obstacle
avoidance
3
2-2. Two visual systems in rodents
• Double dissociation - lesion in visual cortex and in
the superior colliculus
4
• SC for orienting
5
• Visual cortex for pattern discrimination
6
2-3. Two visual systems in frogs
• Two Visual Systems in the Frog
7
• Lesion in the optic tectum induces rewiring.
• Neocortex for obstacle avoidance
• Optic tectum for Response to preys
3. Two cortical visual systems:
Dorsal vs. Ventral
3-1. What and where pathways (Mishkin &
Ungerleider)
• The neurons in the dorsal pathway are selective to
motion and binocular disparity.
• The neurons in the ventral pathway are selective to
shape and color.
8
• Bilateral removal of area TE: Object discrimination -
Which is the unfamiliar object?
• Bilateral removal of posterior parietal cortex:
Landmark discrimination - Which is near to the
landmark?
9
3-2. Vision for perception and vision for action
(Goodale and Milner)
• Dorsal pathway: Vision for action
• Ventral pathway: Vision for perception
10
• Optic ataxia (視覚性運動失調)
• Damage in the posterior parietal cortex -
supramarginal gyrus and angular gyrus
• Orientation error does not depend on hand but on
visual field.
• Damage in the dorsal pathway affects vision for

2. action.
11
• Visual form agnosia (視覚失認):
• Subject DF: Bilateral damage in ventral visual
pathway (Lateral occipital area: LO)
• Very good performance in ‘posting’ task
12
• DF matched her card orientation to the slot during
the course of the movement, well before
contacting the target.
13
• Functional double dissociation
• "Visual phenomenology ... can arise only from
processing in the ventral stream ...
visual-processing modules in the dorsal stream ...
are not normally available to awareness." ("The
visual brain in action" p.200-201)
14
3-3. Perceptual experience in visual agnosia
• Retained color, texture perception
• Degraded form perception
• a piece of kitchen equipment … it’s got a red part
to it, a red handle … it goes down into a silver
corrugated part … the red part’s plastic and the
other part’s metal.” (When she was handed it) “Oh,
it’s a torch.”
15
• She had difficulty in describing her visual
experience, only saying that objects tend to appear
‘blurred’ and that separate elements ‘run into each
other’.
13
4. Blindsight in human
4-1. Case reports
• G.Y. became blind in his right visual field due to
traffic accident in eight years old. He was
diagnosed as homonymous hemianopia.
• Above-chance performance in forced-choice =>
blindsight
16
4-2. Blindsight and two-visual systems
hypothesis
• Access to the dorsal pathway in blindsight
5. Blindsight in monkey
5-1. Blindsight in monkeys
• Blindsight after 2-3 months training
17
• Are the monkeys really ‘blind’ to the visual stimuli?
The monkeys behaved as if it is a No-target trial.
The monkeys are ‘not able to see’, as in human
blindsight.
5-2. Saliency in blindsight
• Monkey without V1: Visually guided reaching
• Frogs with rewired OT: Frogs with rewired OT
• => Visual saliency?
• What is saliency?
• Saliency computational model
18
• Salient stimuli attract gazes of blindsight monkeys
19
• The gaze positions have higher saliency, than
expected from random eye movement.
• What it is like to be blindsight?
• feeling ‘atmosphere’ = saliency without visual
consciousness
• Dual system for conscious vision and saliency.
6. Summary
PART 2
1. How to study consciousness?
1-1 Definition of consciousness
• ?? “Consciousness is not a subject of science
because we cannot define them.”
• Let’s start from a common-sense definition, not
from an analytic definition.
20
• A common-sense definition of consciousness:
"consciousness refers to those states of sentience
or awareness that typically begin when we wake
from a dreamless sleep and continue through the
day …”
1-2 Hard problem of consciousness
• Philosophical zombie
• The inverted spectrum
• * How things that look green to you look red to me
and vice versa.
• * The things we both call red look to you the way
the things we both call green look to me.
• In his (Ned’s) class, ~2/3 of the students usually
say, ‘Oh yeah, I see what you’re talking about’ and
some of them even say, ‘Oh yeah, I’ve wondered
about that since I was a kid.’ ~1/3 of people say, ‘I
don’t know what you’re talking about.’
• The hard problem of consciousness:
• the problem of explaining how and why we have
qualia or phenomenal experiences — how
sensations acquire characteristics, such as colors
and tastes.
• Awareness: “a state wherein we have access to
some information, and can use that information in
the control of behavior.” the psychological concept
of mind”
1-3 Neural correlates of awareness
• An experimental manipulation is required by which
a visual input is constant but perception of that
visual stimulus varies.
• In binocular rivalry, the stimulus is stable but the
content of awareness switches. Then, we can find
the neural correlate of visual awareness by
comparing two different perceptual reports.
• Activity of IT neurons reflects the monkeys’
perceptual report
21
. This is strong evidence that IT
neurons represent content of subjective
experience.
• fMRI during binocular rivalry
22

3. 2. Active vision
2-1 Corollary discharge and Remapping
• We reconstruct images by constantly moving our
eyes.
23,24
• Corollary discharge
• Helmholtz (1866)
• why image motion caused by saccades passes
unnoticed
• Why stability is maintained in spite of shifts in
image position
• Efferent copy (Von Holst and Mittelstaedt 1954)
• Keeping track of one's movements was based on
monitoring outputs to muscles (implication of
exact copy)
• Corollary discharge (Sperry 1950)
• The interaction of "motor patterns" with a
"sensorium" without specifying where the
interaction occurs
• Why can’t you tickle yourself? - Cancellation of
self-produced sensation
• Stability of vision during saccade
• Pre-saccadic remapping in LIP
2-2 Bayesian surprise
• How to evaluate temporal saliency?
• Saliency model evaluates what is salient in an
image in term of spatial configuration.
• How to evaluate what is salient in an image in term
of temporal changes? => Bayesian surprise
• You have a belief about the world: “it is the CNN
news.”
• We get surprised if we have to change our belief of
the world.
• The world becomes boring again.
• Bayesian surprise measures how much your belief
changed by the data.
• Bayesian surprise is defined as the difference
between prior and posterior. =>KL divergence
• Surprise is better predictor than saliency
2-3 Friston’s free energy principle
• The free-energy principle
25
• An organism is able to minimize the free energy by
reducing bayesian surprise (internal state) or by
changing sensation (action).
3. Enactive view
3-1 Sensorimotor contingency theory
• Standard view: Seeing is making an internal
representation
• New view: Seeing is knowing about things to do
26
• Alva Noe のエナクション説
27
：
• Sensorimotor dependence: 私たちが対象に向かっ
て近づくと対象の姿が大きくなる。
• 私たちはこのような sensorimotor dependence に
精通している。
• 私たちの知覚能力は、この種の感覚-運動的知識の
所有によって構成されている。
• 感覚-運動的知識とは命題的なものではなくて、技
能的なもの。(宣言的記憶と手続き記憶)
• 例：開眼手術、逆さメガネ
3-2 Brain or environment, which determines
conscious experience?
• Blindsight = Frog’s consciousness?
• This is an ‘internalist’ view. Brain area determines
which kind of experience is evoked.
• Hurley and Noë’s argument:
28
• Based on Enactive view, sensorimotor contingency,
rather than brain region, is the determinant of
conscious experience.
• This is empirically testable. sensory input ? (=>
Externalism, enactivism) or brain activity? (=>
Internalism)
• Phantom limb: the case for brain activity
• Inverted glass: the case for sensory input
29
• Which occurs in blindsight?
• Internalist view: ‘Feeling of something happening’
is a result of SC activity but it is overridden by
‘redness of red’ in normal subjects. After V1
lesion, it was unmasked.
• Enactive view: ‘Feeling of something happening’
can be a kind of conscious experience
accompanied by functional recovery and
expanded availability of sensorimotor skill.
• 盲視の例は externalist 説を支持しているのではな
いか?
• 1) Please remember blindsight is not available
just after the lesion.
• 2) さらに empirical にテストできる。Normal
subject で V1 を一時的に suppress したら
feeling-of-something は起こるか? 盲視で SC を
一時的に抑えたら何が起こるか?
4. Let’s combine everything
Dorsal: ‘Feeling-of-something-happening’ is shaped
by sensorimotor contingency.
Decision is not consciousness. Evidence
accumulation and action are the same in term of
“active inference”.
Ventral: Conscious experience emerges as an
internal model in predictive coding.
Bottom up attention (or surprise) and consciousness
is the same when they have no prediction error.
5. Hetero-phenomenology (ヘテロ現象学)
•
• Q: How to study consciousness scientifically?
• A (by Dennett): Do it with heterophenomenology.
• 火星から来た科学者(哲学的ゾンビ)が地球人の「意
識経験」について調査しているとする。

4. • 火星人は行動データ、生理データを集める。
• 行動データのうち、言語報告やボタン押しについて
は信念や意図を表しているものとして解釈する
(志向的態度)。
30
• 火星人はこれらのデータから、地球人の意識経験を
フィクションとして再構成する。
• 火星人は地球人の意識経験が実在するかどうかを
問わなくてよいという意味で中立的であると言え
る。
• これは文化人類学者がある部族の宗教を研究する
のに、その宗教を信じなくてもよいのと同じだ。
• この方法は科学の厳密さを失うことを最小限にし
た、意識の三人称的研究法であると言える。
31
• そしてこれこそが現在の実験心理学、認知神経科学
が行っていることそのものである。
• 両眼視野闘争の例
22
• (a) 「顔を見たという意識経験そのもの」
• (b) その意識経験を持ったという信念
• (c) その信念を表出するためにボタンの右を選択
する
• (d) 右ボタンを押す(=「顔を見た」と発声する)
• ヘテロ現象学では(d)という一次データを解釈する
ことで(b)という信念(志向的態度)に到達する。
• どうやって(b)という信念が生まれたかを解明する
ことが意識の科学がするべきこと。
• (a)そのものは問わない。
• もし(a)=(b)でないのなら、(b)に「被験者は言い表
せない信念を持っている」という信念を付け加えれ
ばよい。
6. Neurophenomenology (神経現象学)
• 「意識のハードプロブレムに対する方法論的救済
策」
32
• 意識経験を一人称的かつ誰でも同意できる形で説
明するにはどうすればよいか?
• 三つの統合
• 1) 意識経験の(フッサール)現象学的な分析
• 2) 生物学的システムに関する経験的な実験
• 3) 力学系理論
• なんで力学系か?:
• enactive な認知観：認知は身体を持つ(embodied)
エージェントによって行われ、感覚・運動的活動
によって媒介される。
• => enactive な認知は力学系的な道具立ての中に
自然に収まる (<==> 計算論的)
33
• 現象学的な時間(「生きられた時間」=把持、原印
象、予持)は内部発生的な力学系の中で協調してい
る (=> trajectory によって決まる)
• 神経現象学の実践例：
34
• 1) 被験者は「現象学的還元」によって、事項が経
験される仕方に注目するように訓練する。
• 現象学的還元 = 「主観と客観」の二元論のよう
な形而上学をいったん脇に置いて経験の構造を
反省的に捉えること
• => 現象学的方法は内観主義ではない
• 1)「現象学的還元」の成果として、被験者は発見的
に自分の準備状態について報告できるようになっ
た。このカテゴリーが他の被験者と一貫しているこ
とを確認した。(「相互主観的な確証」)
• 2) 多点での EEG(脳波)の計測
• 3) 力学系的な方法での解析: 試行を平均化しない
ガンマ帯の脳波の phase synchronization
• 現象学的に明らかにされた準備状態によって脳波
の phase synchrony が変わる。
• My criticism:
• 1) 意識状態について「発見的にカテゴリー分け
をする」点以外はヘテロ現象学と違いはない。両
眼視野闘争実験でだって、経験を整理していく際
に「右、左、両方が混ざる」というカテゴリー分
けが出来て、それは被験者に依らず共通。
• 2) 結局のところ「神経相関」であって、力学系
的な「内的に区別可能なカテゴリーの創発」とは
なっていない。
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