언어와두뇌

Language and Brain

• Image from: http://thebrain.mcgill.ca/flash/i/i_10/i_10_cr/i_10_cr_lan/i_10_cr_lan.html

• 신경언어학: Neurolinguistics = study of language in the brain

- 언어처리가두뇌의어느부분에서일어나는지를연구.

• Why do we need to study neurolinguistics?- To understand the parts of the brain controlling the processing of language- To understand how each area in the brain works in the processing of language

뇌의국지화

• Localization (국지화): 다양한인간의능력과행동이두뇌의특정부분에서담당함.

• 국지화의개념은생각보다오래된기원을가짐• Franz Joseph Gall의국지화이론

-인간의다른인지능력과행동은두뇌의다른부분에국지화되어나타남. - Phrenology (골상학): 두뇌에튀어나온부분을연구함으로써인간의성품을논하던학문. -인간의능력은두뇌발달과밀접한연관이있다고생각함.

언어와두뇌

• 뇌기능의편재화 (lateralization) - 좌뇌와우뇌가다른인지기능(cognitive

functions)을담당함.i) 좌뇌의역할- 분석적유추- 일시적인명령에대한판단- 수학적사고- 언어능력- 신체의오른쪽의감각과운동을담당.

ii) 우뇌의역할- 패턴을맞춰보는것- 사람을알아보는것- 시공간인지기능- 신체의왼쪽부분의감각과운동을담당.

국지화(localization)의증거

• 실어증 (aphasia) = 질병이나트라우로인해언어를인지하고처리하는능력을상실하는것.-실어증이있는환자를관찰, 뇌의손상된부분과언어능력상실의관계를살펴봄으로써실어증과국지화를연관지을수있음.

Broca’s aphasia

• Paul Broca (1824 - 1880): French physician-뇌수술이후실어증을겪는환자를관찰-좌뇌의앞쪽부분의손상을입는경우에나타남.

Image from http://neurophilosophy.wordpress.com/2007/04/26/old-brains-new-ideas/

• 특징 (expressive aphasia)

- 말을만들어내는데어려움을겪음. - 비문법적인문장들 (기능어, 의존접사등의상실)

- 틀린어순- 남이말하는것은이해하지만능동태/수동태전환, 비문법적인문장의수정, 기능어이해가어려움.

Example:

Yes . . . ah . . . Monday . . . ah . . . Dad and PeterHogan, and Dad . . . ah . . . hospital . . . and ah . . .Wednesday . . .Wednesday nine o’clock and ahThursday . . . ten o’clock ah doctors . . . two . . . two .. . an doctors and . . . ah . . . teeth . . yah . . . And adoctor an girl . . . and gums, an I.Lower Falls . . . Maine . . . Paper. Four hundred tons aday! And ah . . . sulfur machines, and ah . . . wood . .. Two weeks and eight hours. Eight hours . . . no!Twelve hours, fifteen hours . . . workin . . . workin . . .workin! Yes, and ah . . .sulphur. Sulfur and . . . Ahwood. Ah . . . handlin! And ah sick, four years ago.

Wernicke’s Aphasia

• Karl Wernicke (German neurologist)- 좌뇌의뒤쪽에뇌손상을입은환자들을관찰, 다음과같은실어증의특징을찾아냄.

• 특징(receptive aphasia)- 유창하고문법적인말, 그러나의미없는말의나열임.

- 다른사람의말을잘이해하지못함. - 어휘를사용하는데있어서실수를함. - 의미없는단어를만들어냄

Example:

First of all this is falling down, just about, and is gonna fall downand they’re both getting something to eat...but the trouble is thisis gonna let go and they’re both gonna fall down...I can’t seewell enough but I believe that either she or will have some foodthat’s not good for you and she’s to get some for her, too...andthat you get it there because they shouldn’t go up there and get itunless you tell them that they could have it. And so this is fallingdown and for sure there’s one they’re going to have for food and,and this didn’t come out right, the, uh, the stuff that’ s uh, goodfor, it’s not good for you but it, but you love, um mum mum[smacks lips]... and that so they’ve ...see that, I can’t see whetherit’s in there or not...I think she’s saying, I want two or three, Iwant one, I think, I think so, and so, so she’s gonna get this onefor sure it’s gonna fall down there or whatever, she’s gonna getthat one and, and there, he’s gonna get one himself or more, it alldepends with this when they fall down...and when it falls downthere’s no problem.

실어증요약

Type Damage to Speech Comprehension

Broca’s Broca’s Area Nonfluent GoodAgrammatical

Wernicke’s Wernicke’s Fluent PoorMeaningless

국지화(localization)의또다른증거II: Split Brain patients

-좌/우뇌는 corpus calosum이라부르는많은섬유질다발로이어져있음.

- 40-50년대간질을치료하기위해서 corpus calosum을절단함.

- 좌/우뇌가서로교류하는것을차단함. - 신체의왼쪽에주어지는자극에대해서언어로이야기할수가없음.

More on split-brain patients• 환자가눈가리개를하고물체를오른손에쥠물체가무엇인지알아맞출수있음.

• 물체를왼손에쥐게되는경우언어적으로물체를표현못함

이유: • 오른손에쥔경우: 좌뇌가언어기능을담당, 물체를알아맞출수있음.

• 왼손에쥔경우: 우뇌에만 input이주어짐좌뇌(언어기능을담당)와연결될수있는 corpus callosum이절단되었기때문에좌뇌에서언어를처리할수없음.

언어습득 (language acquisition)

Before what we’ve learned…- 언어는인간의본성이다. - 모든언어는공통적특성을가지고있다. - 인간은유전적으로언어를배울수있는능력이있다.

However…- 언어는사회적/환경적인요소를가지고있다.

국지화의증거 III: dichotic listening

• Dichotic listening (양분청취법)- 실험자에게동시에이어폰을통해두가지다른소리를들려줌.

- 실험자는오른쪽귀로바로전달되는언어자극(linguistic stimuli)을더정확하게맞추고, 왼쪽귀로바로전달되는비언어자극(nonverbal stimuli)을더정확하게알아들음

- 이유???.

국지화의증거 IV: Linguistic savants

• Savants-자폐증등의발달장애와지적장애등의뇌장애를가진사람들중일부는언어, 암기·계산·음악·미술·기계수리등의분야에서천재적인재능을발휘한다. -언어서반트의경우일상생활에서필요로하는사소한기술들을지니고못하는경우가많지만, 언어 (또는외국어)의복잡한문법구조를이해하는데는천재성을드러낸다. -이는곧언어능력은일반적인인지능력과는별개로존재한다는것을보여줌.

Interim Summary • 언어와두뇌는밀접하게연관되어있다. • 두뇌의특정부분이언어능력과밀접하게연관되어있으므로이부분의손상은언어능력의손상으로이어질수있다.

Q: How do we know that the brain, not any other organs, is responsible for language development?

A1: There is a critical period responsible for language acquisition critical period hypothesis

Critical Period Hypothesis

• 언어능력은생물학이고, 모국어습득능력은출생부터유년기에발달한다.

• 결정적시기동안, 언어습득은외부개입없이자연스럽게이루어진다.

• 결정적시기후, 문법의습득은어려워지며모국어화자가지니는 proficiency를가질수없게된다.

언어의진화

• How do we know that the brain, not any other organs, is responsible for language development?

• A2: the evolution of language.

언어탄생의기원 1: 신의산물• 언어의기원

-신의산물??: 각고대신화에서언급됨. (이집트– Thoth, 인도-Sarasvati…)-언어의신비를파헤치는것이얼마나어려운것인가를단적으로보여줌.

• Sumerian의비문: 현존하는가장오래된비문(기원전 4천년전)-그러나문자의기록말고 spoken language의기원은훨씬오래되었을것이라추정됨. Why???현재도문자시스템을가지고있지않은언어들이존재함.

언어탄생의기원 1: 신의산물• 언어의기원

-신의산물??: 각고대신화에서언급됨. (이집트– Thoth, 인도-Sarasvati…)-언어의신비를파헤치는것이얼마나어려운것인가를단적으로보여줌.

• Sumerian의비문: 현존하는가장오래된비문(기원전 4천년전)-그러나문자의기록말고 spoken language의기원은훨씬오래되었을것이라추정됨. Why???현재도문자시스템을가지고있지않은언어들이존재함.

Some interesting points

• 언어가신의산물이란관점-인간의언어가신의언어와같다는전제하에종교의식에서고어들이아직도많이사용됨 (천주교-라틴어, 힌두경전-산스크리트어, 이슬람코란-고전아랍어) -맹목적민족주의의대상이됨. - Tower of Babel

However…• 인류는단일인종/단일언어에서분파한것이아님.

• 고립아/야생아연구: 고립아/야생아들이자발적으로사용하는언어가인간의원어라는가정

-고립아들은이미언어를사용할수있는나이를지나서발견됨. -인간사회와의접촉이없이언어를습득하는것은불가능함. -따라서고립아들이습득한언어가원어라는가정은잘못된것임.

언어의기원 2: 인간의발명물

• Artistotles, Rousseau….-사물에대한명칭은사물의본성과연관지어명명됨. -인간의감정을나타나는감탄사가먼저발명되고나중에복잡한어휘나문장으로발달되었다고생각함. -인간문명의발달에따라인간언어도함께 ‘원시적인’ 형태에서 ‘문명적인’ 형태로발달했을것이라가정.

• 문제점-어느언어의단어수가적거나, 문장구조가단순하다고해서그언어가‘열등하다’거나 ‘원시적’, 또는‘단순하다’라고볼수없음. -언어기원에대하여러학설은일부극소수의어휘출처 (주로의성어에국한된)만을알려줄뿐임.

New hypothesis

• Liberman: 생리학적, 고고/인류학적인접근-언어의이원성(duality -소리와의미가독립된체계를지니고있음)에근거함.앵무새 (의미가결여), 침팬지 (음성기관의미발달)-두뇌의진화와발성기관의진화가언어의언어의기원이밀접하게연관되어있음.

• Evidence -인간두뇌용적의증가원숭이 > Homo erectus (2배) > Homo sapiens (3배)-두뇌용적/지능발달의함수관계: 상보적

Q: 언어출현에얼마만큼의진화된두뇌가필요한가??-단선적(linear) vs. 추적적(tracking) 행동-언어수행: 추적적행동

언어의발생

1. 두뇌의발달• 언어발달이두뇌발달과밀접한연관이있다고볼때, 약 50만년전이라고추정-석기의발달과정으로추정 (정교하게발달한석기)-구석기중엽 (약 50만년전), Levalloisian 법으로만든석기는그이전에만든석기에비해보다정교함 (추적적행동에의해만들어진석기)

2. 발성기관의진화• 인간

- two-tube tract-성문(glottis)이목중간에위치해있음. -혀의위치를다양화함으로써발성기관의상대적크기를변화, 다양한소리를낼수있도록함.

• 영장류- one-tube tract-성문이목위에위치. -제한적인소리만낼수있음.

• 유아의발성기관-성문(glottis)이목보다더높이올라가있음만들어낼수있는소리가성인에비해제한적임.-성인이되면서성문의위치가목아래로내려옴언어발생이발성기관과밀접한관련이있다는것을보여줌.

Conclusion두뇌의진화 + 발성기관의진화 (성문의하강) = 언어의발생

However….• 두뇌의진화와성문의하강이언어발생에영향을주긴했으나, 이러한두가지요소가‘언어발생’을온전한목적으로만진행되었다고볼수는없음.

• 두뇌의진화와발성기관의발달에맞춰인류가여러가지면에서진화를겪게되는과정에서, 언어발생도함께이루어짐.

• 언어 = 소리 (발성기관) + 뜻 (두뇌)