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駒場学部講義 総合情報学特論III 「意識の科学的研究 - 盲視を起点に」


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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)

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駒場学部講義 総合情報学特論III 「意識の科学的研究 - 盲視を起点に」

  1. 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 forperception, 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 10. What is consciousness?-- Let’s start from examples• Salient visual stimuli can disappear.• We are not conscious of all of the signals on theretina.1. What is Blindsight (盲視)?• Q: What is blindsight?• A: “The visually evoked voluntary responses ofpatients with striate cortical destruction that aredemonstrated despite a phenomenal blindness”1• Phenomenal consciousness can be dissociatedfrom visual information processing.2. Two visual systems:Cortical vs. Subcortical2-1. Two visual systems in monkeys• Bilateral lesion in V1 - first report of blindsight inmonkey2• Retained: visually guided reaching and obstacleavoidance32-2. Two visual systems in rodents• Double dissociation - lesion in visual cortex and inthe superior colliculus4• SC for orienting5• Visual cortex for pattern discrimination62-3. Two visual systems in frogs• Two Visual Systems in the Frog7• Lesion in the optic tectum induces rewiring.• Neocortex for obstacle avoidance• Optic tectum for Response to preys3. Two cortical visual systems:Dorsal vs. Ventral3-1. What and where pathways (Mishkin &Ungerleider)• The neurons in the dorsal pathway are selective tomotion and binocular disparity.• The neurons in the ventral pathway are selective toshape 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 thelandmark?93-2. Vision for perception and vision for action(Goodale and Milner)• Dorsal pathway: Vision for action• Ventral pathway: Vision for perception10• 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 onvisual field.• Damage in the dorsal pathway affects vision for
  2. 2. action.11• Visual form agnosia (視覚失認):• Subject DF: Bilateral damage in ventral visualpathway (Lateral occipital area: LO)• Very good performance in ‘posting’ task12• DF matched her card orientation to the slot duringthe course of the movement, well beforecontacting the target.13• Functional double dissociation• "Visual phenomenology ... can arise only fromprocessing in the ventral stream ...visual-processing modules in the dorsal stream ...are not normally available to awareness." ("Thevisual brain in action" p.200-201)143-3. Perceptual experience in visual agnosia• Retained color, texture perception• Degraded form perception• a piece of kitchen equipment … it’s got a red partto it, a red handle … it goes down into a silvercorrugated part … the red part’s plastic and theother part’s metal.” (When she was handed it) “Oh,it’s a torch.”15• She had difficulty in describing her visualexperience, only saying that objects tend to appear‘blurred’ and that separate elements ‘run into eachother’.134. Blindsight in human4-1. Case reports• G.Y. became blind in his right visual field due totraffic accident in eight years old. He wasdiagnosed as homonymous hemianopia.• Above-chance performance in forced-choice =>blindsight164-2. Blindsight and two-visual systemshypothesis• Access to the dorsal pathway in blindsight5. Blindsight in monkey5-1. Blindsight in monkeys• Blindsight after 2-3 months training17• 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 humanblindsight.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 model18• Salient stimuli attract gazes of blindsight monkeys19• The gaze positions have higher saliency, thanexpected from random eye movement.• What it is like to be blindsight?• feeling ‘atmosphere’ = saliency without visualconsciousness• Dual system for conscious vision and saliency.6. SummaryPART 21. How to study consciousness?1-1 Definition of consciousness• ?? “Consciousness is not a subject of sciencebecause we cannot define them.”• Let’s start from a common-sense definition, notfrom an analytic definition.20• A common-sense definition of consciousness:"consciousness refers to those states of sentienceor awareness that typically begin when we wakefrom a dreamless sleep and continue through theday …”1-2 Hard problem of consciousness• Philosophical zombie• The inverted spectrum• * How things that look green to you look red to meand vice versa.• * The things we both call red look to you the waythe things we both call green look to me.• In his (Ned’s) class, ~2/3 of the students usuallysay, ‘Oh yeah, I see what you’re talking about’ andsome of them even say, ‘Oh yeah, I’ve wonderedabout that since I was a kid.’ ~1/3 of people say, ‘Idon’t know what you’re talking about.’• The hard problem of consciousness:• the problem of explaining how and why we havequalia or phenomenal experiences — howsensations acquire characteristics, such as colorsand tastes.• Awareness: “a state wherein we have access tosome information, and can use that information inthe control of behavior.” the psychological conceptof mind”1-3 Neural correlates of awareness• An experimental manipulation is required by whicha visual input is constant but perception of thatvisual stimulus varies.• In binocular rivalry, the stimulus is stable but thecontent of awareness switches. Then, we can findthe neural correlate of visual awareness bycomparing two different perceptual reports.• Activity of IT neurons reflects the monkeys’perceptual report21. This is strong evidence that ITneurons represent content of subjectiveexperience.• fMRI during binocular rivalry22
  3. 3. 2. Active vision2-1 Corollary discharge and Remapping• We reconstruct images by constantly moving oureyes.23,24• Corollary discharge• Helmholtz (1866)• why image motion caused by saccades passesunnoticed• Why stability is maintained in spite of shifts inimage position• Efferent copy (Von Holst and Mittelstaedt 1954)• Keeping track of ones movements was based onmonitoring outputs to muscles (implication ofexact copy)• Corollary discharge (Sperry 1950)• The interaction of "motor patterns" with a"sensorium" without specifying where theinteraction occurs• Why can’t you tickle yourself? - Cancellation ofself-produced sensation• Stability of vision during saccade• Pre-saccadic remapping in LIP2-2 Bayesian surprise• How to evaluate temporal saliency?• Saliency model evaluates what is salient in animage in term of spatial configuration.• How to evaluate what is salient in an image in termof temporal changes? => Bayesian surprise• You have a belief about the world: “it is the CNNnews.”• We get surprised if we have to change our belief ofthe world.• The world becomes boring again.• Bayesian surprise measures how much your beliefchanged by the data.• Bayesian surprise is defined as the differencebetween prior and posterior. =>KL divergence• Surprise is better predictor than saliency2-3 Friston’s free energy principle• The free-energy principle25• An organism is able to minimize the free energy byreducing bayesian surprise (internal state) or bychanging sensation (action).3. Enactive view3-1 Sensorimotor contingency theory• Standard view: Seeing is making an internalrepresentation• New view: Seeing is knowing about things to do26• 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 determinesconscious experience?• Blindsight = Frog’s consciousness?• This is an ‘internalist’ view. Brain area determineswhich kind of experience is evoked.• Hurley and Noë’s argument:28• Based on Enactive view, sensorimotor contingency,rather than brain region, is the determinant ofconscious 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 input29• 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 V1lesion, it was unmasked.• Enactive view: ‘Feeling of something happening’can be a kind of conscious experienceaccompanied by functional recovery andexpanded 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 availablejust after the lesion.• 2) さらに empirical にテストできる。Normalsubject 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 everythingDorsal: ‘Feeling-of-something-happening’ is shapedby sensorimotor contingency.Decision is not consciousness. Evidenceaccumulation and action are the same in term of“active inference”.Ventral: Conscious experience emerges as aninternal model in predictive coding.Bottom up attention (or surprise) and consciousnessis 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. 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。References1. Cowey, A. & Stoerig, P. Blindsight in monkeys.Nature 373, 247–249 (1995).2. Humphrey, N. K. & Weiskrantz, L. Vision inmonkeys after removal of the striate cortex. Nature215, 595–597 (1967).3. Humphrey, N. K. Vision in a monkey without striatecortex: a case study. Perception 3, 241–255(1974).4. Schneider, G. E. Two visual systems. Science 163,895–902 (1969).5. Carman, L. S. & Schneider, G. E. Orientingbehavior in hamsters with lesions of superiorcolliculus, pretectum, and visual cortex. Exp BrainRes 90, 79–91 (1992).6. Schneider, G. E. Mechanisms of functionalrecovery following lesions of visual cortex orsuperior colliculus in neonate and adult hamsters.Brain Behav. Evol. 3, 295–323 (1970).7. Ingle, D. Two Visual Systems in the Frog. Science181, 1053–1055 (1973).8. Van Essen, D. C. & Gallant, J. L. Neuralmechanisms of form and motion processing in theprimate visual system. Neuron 13, 1–10 (1994).9. Mishkin, M., Ungerleider, L. G. & Macko, K. A.Object vision and spatial vision: two corticalpathways. Trends in Neurosciences 6, 414–417(1983).10. Goodale, M. A. & Westwood, D. A. An evolvingview of duplex vision: separate but interactingcortical pathways for perception and action.Current Opinion in Neurobiology 14, 203–211(2004).11. Perenin, M. T. & Vighetto, A. Optic ataxia: aspecific disruption in visuomotor mechanisms. I.Different aspects of the deficit in reaching forobjects. Brain 111 ( Pt 3), 643–674 (1988).
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