NEURAL NETWORK
in Ton H Thn Kinh

Tr thng minh nhn to c th thay
th cho b no ca con ngܩi?

HI SA (HS)


Khong 400 nm trܧc Thin Cha gio (400 BC), Aristotle khi mo cho khi nim v h thng thng minh ca con ngܩi. ng ghi ch "S lin h v ni tip gia tt c nhng tr nh hnh thnh nn tng cn bn cho tt c mi hot Ƕng ca b no" (The associations and links between memories form the basis for most conscious mental activities). iu ny chnh l yu t cho vic nghin cu v s thng minh nhn to. Nm 1943 hai nh khoa hc gia ca i hc Massachusetts Institute of Technology (M.I.T.), ng Warren S. McCulloch chuyn v "Thn Kinh hc" (Neurology), v ng Walter Pitts l mt nh ton hc v trit hc. Hai ng vit mt lun n "A Logical Calculus of the Ideas Immant in Nervous Activity" ("L lun tnh ton ca nhng t tܪng trong s hot Ƕng ca h thn kinh"). Qua lun n ny hai ng ܮc cc nh khoa hc gia ǥt cho l "McCulloch-Pitt Neuron". V tnh cht ny chnh l nn tng cho cu trc ca "Neural Network".

"Neural Network" khng phi l tn ca mt h thng kinh lc in t (Local Area Network, LAN). "Neural Network" dng Nj ch cho h thng hot Ƕng ca thn kinh qua cc t bo ܮc mnh danh l "Neuron" (N-rng). Nu i su vo chi tit k thut ta s thy nhng anh chng neuron ny c nhng tnh cht tng t nh nhng huyt o ca ng chng ta. Trong b no ca mt ngܩi trܪng thnh c ti 100 t (billion) t bo neuron ny. S thng minh lanh l ca chng ta nh vo tnh cht ca h thng neuron ny y, ܮc gi l "neural network" (h thn kinh).

Nh vy, cc bn chc s t hi v s lin quan gia h thn kinh ny vi ngnh in ton ngy nay. Trong thp nin 40, bn cnh s pht trin ca ngnh in ton, con ngܩi mun ch to mt b my c tr thng minh nh chng ta, m ngy nay ܮc coi l ngnh "Artificial Intelligence" (Tr Thng Minh Nhn To). Nh vo "McCulloch-Pitt Neuron" mt kin trc in ton mi ra ǩi, kin trc ny da vo k thut hot Ƕng ca cc anh chng neuron, v ܮc gi l "Neural Network", nu dch ra l h thn kinh khng thi th chng ta rt d b hiu lm nn HS tm dch l "in ton h thn kinh".

Cc bn chc s ngc nhin v ngh rng, cu trc in ton h thn kinh ܮc khai ph t thp nin 40 ti by gi l hn 50 nm (na th k) m sao bn khng h nghe thy ni ti. Ch mi gn y bn mi thy cc bo ch k thut n o ni v k thut in ton thn kinh h ny. V bn ngh n phi tin xa lm ch. Nh vy l do g khin ngnh k thut ny chm chp th?

Mun tm hiu v kin trc ca in ton h thn kinh, trܧc ht chng ta phi tm hiu v s hot Ƕng ca b my tnh ton trong b no chng ta v y chnh l yu t chnh trong vic to ra mt h thng k thut c tr thng minh nhn to.

Theo kin trc cn bn ca h thng in ton xa, vic to ra mt tr thng minh nhn to c phn kh khn v s gii hn h thng ny. Tt c cc s phn tch trong h thng "data processing" Nj a ljn mt kt lun hay mt quyt nh cho mt vn NJ NJu ܮc "program" trܧc. Nh vy mi qui nh NJu phi da vo ngܩi vit "program", v h cn phi c kin thc v mi vn NJ. Thܩng vic gii bt c mt vn NJ g cng NJu c ba giai on.

Th nht, tt c cc d kin n nh trong mt vn NJ cn ܮc gi l b d kin (data set) cn phi ܮc ǥt ra v n nh r rng. Th nh, tt c cc phng trnh dng cho vic phn tch b d kin ny cng phi ܮc quy nh. V th ba, mi dch v v hot Ƕng da vo b d kin Nj iu khin h thng cho vn NJ. Tt c cc vn NJ NJu c bn cht v lnh vc khc nhau, nhng s phn tch v quyt nh trong nhng vn NJ NJu da vo ba yu t trn. Ba yu t ny l ba yu t rt cn bn trong mt h thng ܮc gi l "axiomatic" (axiomatic system, da trn tnh cht phn tch v quyt nh ca mi vn NJ).

Nh vy bn thy mun thit k mt h thng thng minh nhn to c th gii bt c mt vn NJ g. H thng ny khng ܮc n gin v cn c triu "program" khc nhau, v vy cc nh khoa hc tin rng cch hay nht l chng ta thit k mt h thng c c cu hot Ƕng tng t nh b c ca chng ta.

S nhn thc trong b c chng ta NJu da vo c cu hot Ƕng ca cc t bo n-rng. Cc t bo n-rng c dng nh r cy. N-rng c rt nhiu loi v dng thc khc nhau, nhng cu trc cn bn ca mt n-rng c bn phn "Motor neuron" (n-rng Ƕng c), "spinal cord", "sensory neuron" (n-rng cm nhn), v "end organ" (bao gm cc synapses, ni mang nhim v bn cc tn hiu Nj truyn tin i). Cu trc cng nh nghin cu v tm hiu v hot Ƕng ca cc n-rng l mt vn NJ rt su rng. y, chng ta ch cn bit nhng vn NJ tng quan trong vic thit k mt b my in ton h thn kinh. Cc chui n-rng ܮc ni vi nhau nhng li khng dnh vo vi nhau. Mi d kin tn hiu ܮc thuyn chuyn qua li gia cc n-rng qua phn "end organ".

Tt c trm t t bo n-rng ny ܮc ni lin vi nhau nh h thng kinh lc (network) to thnh s thng minh ca mi ngܩi chng ta. S sng to, tim thc, hnh Ƕng, suy ngh, tr nh.. NJu t y xut ra. Mi d kin hnh nh, m thanh v nhng cm nhn khc ܮc tip nhn, t y tt c cc d kin ny ܮc lc li, hc hi, so snh vi kinh nghim trܧc Nj i ljn mt kt lun, v quy nh cho mt hnh Ƕng ܮc thi hnh ty theo s n nh ca b no.

i su vo nhng phng thc suy lun v lm vic ca b no. N c th nhn cc d kin v uyn chuyn tnh ton Nj p ng vi nhng bi ton kh khn, m i khi mt b my in ton ti tn nht ly c gi hoc ngy, nm Nj gii, c khi cn khng gii ra ܮc " Bn ngc nhin v hi "C tht khng? Sao my tnh cng, tr, nhn, chia lm ton l hn chng ta m."

ng vy, nu ly mt "Program" vi nhng qui lut r rng vi mt phng thc n nh th chng ta s chm hn my mc rt nhiu. V nhng phn ng v s thuyn chuyn cc tn hiu qua cc t bo n-rng chm hn cc tn hiu in trong cc b my in t. Nhng nu ly mt vn NJ cn c s nhn thc (Perception) v nh ot th chng ta mau l v ti tnh hn tt c nhng b my in ton ti tn nht hin nay. l nh kh nng hc hi, suy xt, phi hp cc d kin sai s Nj uyn chuyn thay ǰi phng thc hu gim thiu s sai lm ti a ri i ljn mt kt lun cho bi ton.

Th d ly hai vt th, vi s quan st v so snh, trong khonh khc chng ta c th i ljn kt lun hai vt hon ton khc nhau, hon ton ging nhau, hoc ng dng vi nhau nhng khc v kch thܧc. i ljn kt lun ny mt b my in ton ti tn nht phi ܮc trang b nhng "programs" phc tp Nj ng u vi bi ton loi ny, v n cng phi mt mt thi gian di Nj i ljn cng mt kt lun nh chng ta, i khi cn khng kim ra na. Bn th tܪng tܮng bi ton l mt tr chi xp ǥt nhng ming "puzzles" ca mt tm hnh hoc bi ton cho mt vt th ba chiu th b my in ton chc phi chy ljn Ƕ x hi v bc khi.

Chnh kh nng nhn thc (perception), nht l kh nng hc hi lm cc nh khoa hc gia mun thit k mt b my c cu trc "kinh lc" ca n-rng vi hy vng c ܮc mt my in ton thn k nh b c ca chng ta. Nhng tht bi trܧc thp nin 60 do s phc tp ca b no v s hiu bit gii hn v cc hot Ƕng ca b no cng lc tin dnh cho cuc nghin cu ca chng trnh ny cn khin cho cng cuc pht trin v in ton h thn kinh b ngng li. Mi cho ti nm 1969, hai nh nghin cu Marvin Minsky v Seymour Papert ca M.I.T. cho xut bn quyn sch nhan NJ "Perceptrons". Ni dung ni v s nhn thc (Perception) trong kin trc ca Thn Kinh H (h thng Neural Network Architectures). S kin ny khi mo li vn NJ in ton h thn kinh, vo gia thp nin 80 ti "Caltechs Physics of Computation Lab", ng Carver Mead bt u NJ xܧng ra nhng cu trc cn bn cho mch in n-rng nhn to. Sau mܩi nm nghin cu nh vo k thut hin i Nj vܮt qua mi kh khn v tr ngi, ng Mead vi anh Chris Diorio, k s thit k (Design Engineer) thnh cng trong vic thit k mt mch in nhi to (emulate) phn "suy tܪng" (thinking) trong b c, ting khoa hc gi l "Cerebral Cortex" " y l phn phc tp nht ca b c. Mch in ny c cu trc ca nhng "transistor" (trn st to) mnh danh l "Mushy Transistor" dng Nj "simulate" s hot Ƕng "Synapse" ca t bo n-rng.

Vi nhng kt qu kh quan ca nhiu lnh vc k thut khc chng ta thy nhng p dng li ch cho ǩi sng ca con ngܩi " V t hi n c th thay th ܮc cho b c ca chng ta?

C l vic ng dng nhiu nht l trong vic nhn nh hnh (Pattern Recognition). Trong vic nhn mt ch, tm ܩng trong ha thnh ph v.v... Nhn mt ch coi vy ch rt l phc tp " bn t hi xem ti sao bn nhn mt ch "A" bt c hiu ch no hoc ch vit ca bt c ai, m bn nhn ra l ch "A". i vi bn c l rt d nhng i vi b my li l mt cng vic cc k kh khn. L d nhin bn c th lm li, v b my cng th nhng ci hay l bn v b my NJu hc hi ܮc li lm ca mnh Nj trnh i cho ln ti.

Trong k thut xe hi. Hng volvo dng mt "programs" p dng k thut "in ton h thn kinh" Nj nghe ting my n qua mt "microphone", dng m thanh Nj phn tch v kim ra ch h ca my xe.

Ngay c trong h thng tin bc, First U.S.A. Bank dng k thut ny Nj kim ra nhng k la o trong vic dng credit card Nj thuyn chuyn tin bt hp php.

Nh trn ni v "Pattern Recognition" vi k thut ny, hng "Mitshubishi Electric" ca Nht vit program Nj nhn ra 200 mt ch "Alphabet" vi t l 95 phn trm ng.

Khng nhng th "Wallace " Athony Investment Management" mt hng "khuyn gii u t" (Investment Advisory) dng k thut program ny Nj tin on v nhng th trܩng kinh t v.v...

Hin nay k thut in ton h thn kinh ܮc phi hp vi k thut "lun l m m" hay "Lun l giao thoa" (Fuzzy Logic " Trong bi "Ton hc v thc" ca H.S. trܧc c ni qua v s p dng ca k thut ny). S d gi l "Lun l giao thoa", v tnh cht na chng xun ca n. Trng thi ny khng ܮc n nh r. Chng hn khi ta ni "m" hoc "m m", ch ny khng nh r trng thi ca nhit Ƕ, v i khi n cn ty vo mi trܩng chung quanh. Trong con ngܩi y ry nhng giao thoa lun l, nn rt ph hp vi tnh cht k thut ca in ton h thn kinh. Do , vic phi hp k thut lun l giao thoa vi in ton h thn kinh ha hn mt bܧc tin kh quan trng trong ngnh tr thng minh nhn to (Artificial Intelligence " ܮc gi tt l AI).

Ni v p dng ca in ton h thn kinh th trng giang i hi, mt trong nhng k thut v y ha hn ca th k th 21 sp ljn. Tuy vy n khng th hon ton thay th cho b c ca chng ta ܮc, nhng n l cha kha ch yu gip chng ta m nhng cnh ca khoa hc trng yu trong tng lai. Vi s tin b ca khoa hc hin nay liu cc b c ca loi ngܩi c th hc v bnh trܧng kp vi s lܮng k thut thng tin nhiu v mau l nh vy?


Ch thch: Nhng d kin v chi tit k thut ܮc nghin cu v da trn cc ti liu ca trong s ǥc bit "Mind and Brain" ca tp san "SCIENTIFIC AMERICAN" (thng chn 1992), tp k thut "ARTIFICIAL INTELLIGENCE", sch "The Physiology of Nerve Cells", sch "Computer Sementics", sch "Intelligent System: Applications and Analysis" bo k thut "Electronic Engineering TIMES". Cc danh t k thut ܮc ǥt ra theo tnh cht ca mi danh t. Hy vng tng lai chng ta c th ng nht trong vic n nh cc ch k thut mi.


VIET Magazine 414 Home Page