Language & Brain Chomsky 1959 Why bother? What could we learn? • something about how language works • something about how the brain works • nothing (interdisciplinary cross-sterilization)
Ha Hand s sca canner Phrenology (bad idea) Organology (good idea) Franz Josef Gall 1758-1828
Two enduring ideas deriving from Gall • Faculty psychology The mind has a ‘parts list.’ • Experience-dependent plasticity Using the parts changes their neuronal realization.
The wave of the past “Intuitive psychological organology ”
Phineas Gage, 1848 Before: responsible, well- mannered, well-liked, efficient worker, pious After: capricious, impulsive, irreverent, hypersexual Damage involved VMPFC
Paul Broca 1861, 1865
Leborgne’s (Tan’s) brain
Geschwind 1985
The visual and auditory systems are highly articulated. Is there any a priori reason to believe that language will be an order of magnitude simpler, captured by two brain areas? Auditory system (Hackett) Visual system (van Essen) Broca’s Area Wernicke’s Are “production” “reception” Functional anatomy of speech perception. “syntax” “semantics” Hickok & Poeppel 2007
Positron emission tomography Excellent spatial (PET) resolution (<1 mm) Hemodynamic Limited temporal techniques resolution (~1sec) Functional magnetic resonance imaging (fMRI) Non-invasive recording from human brain (Functional brain imaging) Electro- encephalography (EEG) Limited spatial Electro-magnetic resolution (<1 cm) techniques Excellent temporal resolution (<1msec) Magneto- encephalography (MEG) D. Poeppel , A. Braun et al.
Language is not monolithic language-o-topy Phonetics/phonology sound structure Morphology word structure Lexical semantics word meaning Syntax sentence structure Prosody sentence melody Compositional semantics sentence meaning Discourse larger meaning scale
The wave of the past The wave of the present “Intuitive psychological organology ” “Cognitive psychological organology” phonology syntax semantics
Is there a future? Problems for interdisciplinarity and unification I Linguistics Neuroscience Fundamental elements of representation distinctive feature dendrites, spines syllable neuron ? morpheme cell-assembly/ensemble noun phrase population clause cortical column Fundamental operations on primitives ? concatenation long-term potentiation linearization receptive field phrase-structure generation oscillation semantic composition synchronization There is an absence of ‘linking hypotheses’ by which we explore how brain mechanisms form the basis for linguistic computation. Aligning the alphabets or primitives or atoms is a formidable challenge.
Is there a future? Problems for interdisciplinarity and unification II Why are there no linking hypotheses? Granularity Mismatch Problem (neurolinguistics in practice): Linguistic and neuroimaging studies of language operate with objects of different granularity. linguistics --- fine-grained distinctions neuroscience --- broader conceptual distinctions Neuroscience cannot succeed in seeking “syntax” (or “phonology”) because syntax etc. are not monolithic but have many parts. Ontological Incommensurability Problem (neurolinguistics in principle): The units of linguistic computation and the units of neurobio- logical computation are incommensurable. Therefore, an attempt at reduction makes no sense. Poeppel & Embick, 2005
Is there a future? Problems for interdisciplinarity and unification III Linguistics Neuroscience distinctive feature dendrites, spines morpheme cell-assembly/ensemble noun phrase population ? clause cortical column concatenation long-term potentiation linearization receptive field phrase-structure generation oscillation semantic composition synchronization fractionate into identify basis for generic formal operations generic formal operations segmentation segmentation concatenation concatenation comparison comparison recursion recursion
Is there a future? Problems for interdisciplinarity and unification IV Desiderata for a model bridging neuronal mechanisms and linguistic representation Neurobiological mechanisms that can form the basis of elemental steps involved in most linguistic computation: concatenation constituency recursion z x---y y x This is the granularity - and level of abstractness - of operations that can profitably be studied in animal research as well, doing away with questions such as “are humans different or better or higher, or not” and turning to the typical questions such as: “How does this work?”
Putative primitives - the view on irreducible representations and operations from semantics (Pietroski) and syntax (Hornstein) • Variables, a way to link variables • One-place predicates, thematic roles • Operation with the power of conjunction and existential closure • Concatenation (a-directional) • Labeling: concatenate turns into one of its constituents • Some mechanism (copy) to deal with positional specificity of variables
‘Unification Problem’ computational algorithmic implementational Marr’s computational approach permits development of linking hypotheses
Is there a future? Problems for interdisciplinarity and unification V How much can be gained by focusing only on localization by way of imaging? Not much, at this point - it is the ‘homework problem’, that is, an important but ultimately uninteresting step from the point of view of explanation . Can we achieve unification by working on localization? No! We need explicit linking hypotheses between well characterized brain mechanisms and linguistic computation. WRONG QUESTION: where are syntax/phonology/ semantics mediated? RIGHT QUESTION: what kind of computations in the brain form the basis of linguistic representations and operations?
There is localisation, but what is localized is tissue that executes specific computations, such as, say, addition (xxx) or subtraction (zzz) or division (qq), over representations (data structures) of certain types. sss sss qqqq zzzz qqq xx yy zzz xxx yy ppppp oojjjoo pppp oooojj ooooojjjj The cognitive faculties (the “parts” of the human cognome) are not monolithic but composed of multiple computational subroutines.
The wave of the past The wave of the present “Intuitive psychological organology ” “Cognitive psychological organology” phonology syntax semantics The wave of the future “Computational organology” linearization ��� � � � sequencing ��� ÷÷÷ recursion ÷÷÷ Localization of generic constituency computational subroutines
(a) (b) (d) c a t x x x [+ cons, -son] [-cons, +son] [+ cons, -son] (c) [-cont] [-cont] ? LAR/PHAR PLACE LAR/PHAR PLACE LAR/PHAR PLACE [-ATR] GLOT DORSAL DORSAL GLOT CORONAL phonological primal sketch [-voice] [-back, -high, +low]] [-voice] [+ant]
Functional anatomy of speech sound processing Hickok & Poeppel, 2007, Nat Rev Neurosci
Functional anatomy of speech sound processing Hickok & Poeppel, 2007, Nat Rev Neurosci
Functional anatomy of speech sound processing Hickok & Poeppel, 2007, Nat Rev Neurosci
Functional anatomy of speech sound processing Hickok & Poeppel, 2007, Nat Rev Neurosci
Functional anatomy of speech sound processing Hickok & Poeppel, 2007, Nat Rev Neurosci
Functional anatomy of speech sound processing Hickok & Poeppel, 2007, Nat Rev Neurosci
Functional anatomy of speech sound processing Hickok & Poeppel, 2007, Nat Rev Neurosci
Functional anatomy of speech sound processing Hickok & Poeppel, 2007, Nat Rev Neurosci
Hickok & Poeppel, 2007, Nat Rev Neurosci Lau et al. 2008, Nat Rev Neurosci
Newton, Principia Our intuition Our brain Our brain, really
Neuromagnetic activity is recorded from the whole head (160 channels) Sagittal View Axial View
MEG: From signals to magnetic field maps to sources
Phase Patterns of Neuronal Responses Reliably Discriminate Speech in Human Auditory Cortex Huan Luo & David Poeppel
Single-unit responses robustly encode conspecific vocalizations Narayan et al., J. Neurophys. 2006 Zebra Finch (Field L) “Many natural sounds including vocal communication sounds display striking time-varying structure over multiple time scales” “We demonstrate the existence of distinct time scales for Machens et al., Nat. Neurosci. 2003 temporal resolution and temporal integration and explain Grasshopper (peripheral auditory how they arise from cortical neural responses to complex neurons) dynamic sounds.” [~10 ms and ~ 500 ms]
Design: evaluate coherence across single trials elicited by sentences Luo & Poeppel, Neuron, 2007
Theta phase Luo & Poeppel, Neuron, 2007
Theta phase has the sensitivity to discriminate based on single trials Materials: Smith, Delgutte, and Oxenham, Nature , 2002 Luo & Poeppel, Neuron, 2007
Theta phase tracking displays the specificity to discriminate sentences Classification analysis Luo & Poeppel, Neuron, 2007
Recommend
More recommend
