ScienceWeek

SCIENCEWEEK

ScienceWeek
December 27, 2002
Vol. 6 Number 52

An Online Research Digest Published Weekly Since 1997

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What constitutes proof in one generation is not the same thing as
proof in another.
-- Fred Hoyle (1915-2001)

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Section 1

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Thematic Issue: Neurobiology of Language

1. Introduction.
2. Computational and Evolutionary Aspects of Language.
3. On the Origins of Human Language.
4. On the Acquisition of Language by Children.
5. On the Critical Period Hypothesis of Language Acquisition.
6. On the Neurobiology of Cognition.
7. Language Discrimination by Human Newborns and Monkeys.
8. An Innate Basis for Language?
9. On Language-Related Cortex in Deaf Individuals.
10. Old vs. New Views of Language Acquisition.
11. Mirror Neurons and Language Acquisition.
12. Grammar, Language, and Words.

Notices and Subscription Information

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Section 2

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1. INTRODUCTION.

From the Editor: Understanding the neurobiology of language is
perhaps the major challenge of neuroscience. Language, after all,
is the primary means by which the human species receives
information, synthesizes information, and produces information,
processes whose underlying neural events will most likely prove
to be as complex as the processes themselves. From the standpoint
of fundamental physics and chemistry, the simple act of your
reading and understanding these words is a series of events both
formidable and amazing. Although we are still far from a clear
vision of what is happening, there has been much progress in both
theory and experimental technique. -- Dan Agin (Editor).

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"We cannot escape the fact that we are the product of propitious
circumstances molded by the laws of natural selection. The secret
of human evolution is extreme adaptability, and the simple
physical change that made this possible was the liberation of the
hands from the basic function of locomotion. The implications of
this modest behavioral change are enormous, for not only does it
open the way to technology through the manufacture and
manipulation of tools, but it means that the development of
language becomes feasible when appropriate selective pressures
are operating: a mouth that is adapted to help procure food,
carry objects, and threaten or exert aggression, is unlikely to
be able to articulate complex sounds. By our definition,
competent manipulative hands and a sophisticated language are
essential faculties to a cultural animal: the two faculties
combine to permit intentional shaping of the environment to
chosen patterns."

R.E. Leakey and R. Lewin: Origins. E.P. Dutton. 1977. p. 38

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"For as far back as we can trace his history, Man has always
spoken many different languages. If at one time he spoke a single
language, from which all other languages subsequently descended,
linguistic science is unlikely to uncover any hard evidence to
confirm such a fact. In the 19th century scholars made a
concerted effort to reconstruct what was then assumed to be Man's
original language. Major contemporary languages were exhaustively
analyzed in the hope of discovering some common elements that
might point to a single primeval source. Languages of isolated
primitive peoples were examined in the hope of finding a
revealing 'fossil' tongue. But the search was in vain. Today
linguists realize that a clear picture simply cannot be obtained
of events that occurred perhaps a million years ago. We are faced
with a complete lack of data about the beginnings of language,
and any study of its subsequent evolution must be confined to the
more recent historical period. Yet even in this limited aspect of
the inquiry, we find ourselves confronted with a myriad of
languages. At present the languages of the world number in the
thousands. To establish an exact or even an approximate number is
out of the question, for many are scarcely known and it is
impossible to draw a clear-cut distinction between language and
dialect. In many cases, as one travels across a region the
language gradually merges into a neighboring one and it becomes
impossible to state for certain just what language is being
spoken. But although exact numbers are unavailable, we do know
that the American Indian languages number more than a thousand,
the languages of Africa close to a thousand, and the single
island of New Guinea contributes some 700 more. India has over
150, the [former] Soviet Union 130, while China has several
dozen, as do a number of other countries. Even in the United
States more than fifty different Indian languages are spoken."

Kenneth Katzner: The Languages of the World. Routledge & Kegan
Paul. 1977. p. viii.

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"The analogy between the genetic code and human language is
remarkable. Spoken utterances are composed of a sequence of a
rather small number of unit sounds, or phonemes (represented, at
least roughly, by the letters of the alphabet). The sequence of
these phonemes first specifies different words, and then, through
syntax, the meanings of sentences. By this system, the sequence
of a small number of kinds of unit can convey an indefinitely
large number of meanings. The genetic message is composed of a
linear sequence of only four kinds of unit. This sequence is
first translated, via the code, into a sequence of 20 kinds of
amino acid. These strings of amino acids fold to form three-
dimensional functional proteins. Through gene regulation, the
right proteins are made at the right times and places, and an
indefinite number of morphologies can be specified. Thus in both
systems a linear sequence of a small number of kinds of unit can
specify an indefinitely large number of outcomes. But there is
one respect in which the two systems cannot usefully be compared.
In language, the meanings of sentences depend on the rules of
syntax. These rules are formal and logical. In contrast, the
'meaning' of the genetic message cannot be derived by logical
reasoning. Thus, although the amino acid sequence of the proteins
can be simply derived from the genetic message, the way they fold
up to form three-dimensional structures, and the chemical
reactions they catalyze, depend on complex dynamic processes
determined by the laws of physics and chemistry. It does not seem
possible to draw a useful comparison between the way in which
meaning emerges from syntax, and that in which chemical
properties emerge from the genetic code."

John Maynard Smith and Eors Szathmary: The Origins of Life.
Oxford University Press. 1999.  p.169.

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"The human ability to speak is universal. All normal children
acquire the language of their environment at a very early age.
Most start babbling at the age of 7 months, produce a few
meaningful words around their first birthday, reach a 50-word
vocabulary 6 months later, produce their first multi-word
utterances by the end of their second year of life, and begin
expressing syntactic relations by means of prepositions,
auxiliaries, inflections, and word order in the course of their
third year. By the age of 5 or 6, the basic architecture of this
natural skill is essentially in place. Although our ability to
speak has for millennia been recognized as uniquely human, as
species-specific, as the basis of our cultural evolution, and
generally as a core aspect of the human condition (homo loquens),
the systematic study of how we speak did not begin before the end
of the 19th century. In 1900, Wilhelm Wundt [1832-1920] published
his theory about how a sentence emerges in the speaker's mind, a
theory entirely based on introspection. With their 1896
monograph, Meringer and Mayer initiated an important empirical
paradigm. They collected and analyzed a large corpus of
spontaneously produced speech errors that they had carefully
noted down. One of their findings was that word substitutions
were either meaning-based [e.g., (Ihre) your for (meine) mine] or
form-based [e.g., Studien (studies) for Stunden (hours)],
suggesting a distinction between meaning- and form-based
operations in word generation. It was only by the 1970s that this
paradigm became fully exploited to construct theories of
utterance generation."

Willem J.M. Levelt: "Spoken Word Production: A Theory of Lexical
Access." Proc. Nat. Acad. Sci. 2001 98:13464

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2. COMPUTATIONAL AND EVOLUTIONARY ASPECTS OF LANGUAGE.

M.A. Nowak et al (Institute for Advanced Study, US) discuss
language, the authors making the following points:

1) Language is our legacy. It is the main evolutionary
contribution of humans, and perhaps the most interesting trait
that has emerged in the past 500 million years. Understanding how
Darwinian evolution gives rise to human language requires the
integration of formal language theory, learning theory and
evolutionary dynamics. Formal language theory provides a
mathematical description of language and grammar. Learning theory
formalizes the task of language acquisition -- it can be shown
that no procedure can learn an unrestricted set of languages.
Universal grammar specifies the restricted set of languages
learnable by the human brain. Evolutionary dynamics can be
formulated to describe the cultural evolution of language and the
biological evolution of universal grammar.

2) Biology uses generative systems. Genomes consist of an
alphabet of four nucleotides, which, together with certain rules
for how to produce proteins and organize cells, generates an
unlimited variety of living organisms. For more than 3 billion
years, evolution of life on Earth was restricted to using this
generative system. Only very recently another generative system
emerged, which led to a new mode of evolution. This other system
is human language. It enables us to transfer unlimited non-
genetic information among individuals, and it gives rise to
cultural evolution.

3) N. Chomsky (1972) pointed out that the environmental input
available to the child does not uniquely specify the grammatical
rules. This phenomenon is known as "poverty of stimulus". "The
paradox of language acquisition" is that children of the same
speech community reliably grow up to speak the same language. The
proposed solution is that children learn the correct grammar by
choosing from a restricted set of candidate grammars. The
"theory" of this restricted set is "universal grammar". Formally,
universal grammar is not a grammar, but a theory of a collection
of grammars.

4) Ideas of language should be discussed in the context of
acquisition, and ideas of acquisition in the context of
evolution. Some theoretical questions are: what is the interplay
between the biological evolution of universal grammar and the
cultural evolution of language? What is the mechanism for
adaptation among the various languages generated by a given
universal grammar? Some empirical questions are: what is the
actual language learning algorithm used by humans? What are the
restrictions imposed by universal grammar? Can we identify genes
that are crucial for linguistic or other cognitive functions?
What can we say about the evolution of those genes? The study of
language as a biological phenomenon will bring together people
from many disciplines, including linguistics, cognitive science,
psychology, genetics, animal behaviour, evolutionary biology,
neurobiology and computer science. Fortunately we have language
to talk to each other (1-5).

References (abridged):

1. Pinker, S. & Bloom, A. Natural language and natural selection.
Behav. Brain Sci. 13, 707-784.

2. Jackendoff, R. Possible stages in the evolution of the
language capacity. Trends Cogn. Sci. 3, 272-279 (1999).

3. Bickerton, D. Language and Species (Univ. Chicago Press,
Chicago, 1990).

4. Lightfoot, D. The Development of Language: Acquisition,
Changes and Evolution (Blackwell, Oxford, 1999).

5. Brandon, R. & Hornstein, N. From icon to symbol: Some
speculations on the evolution of natural language. Phil. Biol. 1,
169-189 (1986).

Nature 2002 417:611.

Related Background Brief:

NATIVE LANGUAGE, GENDER, AND FUNCTIONAL ORGANIZATION OF THE
AUDITORY CORTEX. The authors report that whole-head
magnetoencephalography was employed in 40 normal subjects to
investigate whether the basic functional organization of the
auditory cortex varies with linguistic environment. Robust
activations of the bilateral supratemporal auditory cortices to
1-kHz pure tones, maximum at about 100 ms after stimulus onset,
were studied in Finnish and German female and male subject groups
with monolingual background. Activations elicited by the tones
were mutually indistinguishable in German and Finnish women. In
contrast, German men showed significantly stronger auditory
responses to pure tones in the left, language-dominant hemisphere
than Finnish men. The authors discuss the possibility that the
prominent left-hemisphere activation in German males reflects
higher frequency resolution required for distinguishing between
German than Finnish vowels and that the clear effect of native
language in male but not in female auditory cortex derives from
more pronounced functional lateralization in men. The authors
suggest the present data indicate that the influence of native
language can extend to auditory cortical processing of pure-tone
stimuli with no linguistic content and that this effect is
conspicuous in the male brain. R. Salmelin et al: Proc. Nat.
Acad. Sci.1999 96:10460.

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3. ON ORIGINS OF HUMAN LANGUAGE

A view currently held by many anthropologists and linguistics
researchers is that the remarkable flexibility of human language
is achieved at least in part through the human invention of
grammar, a recursive set of rules that allows the generation of
sentences of any desired complexity. The linguist Noam Chomsky
has attributed this to a unique human endowment termed "universal
grammar", with Chomsky suggesting that all human languages are
variants of this fundamental endowment.

Michael C. Corballis (University of Auckland, NZ) presents a
review of current ideas concerning the origins of human language,
with emphasis on a scenario involving gestural antecedents. The
author makes the following points:

1) There is little doubt that the great apes (orang-utan,
gorilla, chimpanzee) (and perhaps other species such as dolphins)
can use symbols to represent actions and objects in the real
world, but these animals lack nearly all the other ingredients of
true language.

2) Since the common ancestor of human beings and chimpanzees
lived approximately 5 million years ago, it is a reasonable
inference that grammatical language must have evolved in the
hominid line (i.e., the line of human primates) at some point
following the split from the line that led to the modern
chimpanzee. There has been much disagreement as to when this
might have happened.

3) One major view holds that it is impossible to conceive of
grammar as having been formed incrementally; grammar therefore
must have evolved as a single catastrophic event, probably late
in hominid evolution. But many researchers hold a contrary view,
that language evolved gradually, shaped by natural selection, and
that the cognitive prerequisites of language are already present
in the great apes and antedated the split of our hominid
ancestors from the chimpanzee line, probably by several million
years.

4) The author suggests that at least a partial reconciliation of
these alternative perspectives may be that language emerged not
from vocalization, but from manual gestures, and switched to a
vocal mode relatively recently in hominid evolution, perhaps with
the emergence of Homo sapiens. This is an old idea, apparently
first suggested by Condillac in the 17th century, but argument in
its favor has continued to grow.

5) The author points out that there are countless different sign
languages invented by deaf people all over the world, and there
is little doubt that these are genuine languages with fully
developed grammars. The spontaneous emergence of sign languages
among deaf communities everywhere confirms that gestural
communication is as natural to the human condition as is spoken
language. Indeed, children exposed from an early age only to sign
language go through the same basic stages of acquisition as
children learning to speak, including a stage when they "babble"
silently in sign.

6) The authors proposes the following speculative scenario
concerning the historical development of human language:

... ... a) 6 or 7 million years ago: Simple gestures first
anticipated more complex forms of communication, shortly after
the human line diverged from the great apes. At this stage
vocalizations served only as emotional cries and alarm calls.

... ... b) Approximately 5 million years ago: With the advent of
bipedalism, a more sophisticated form of gesturing involving hand
signals may have evolved among the early hominids now labeled as
"Australopithecus".

 ... ... c) Approximately 2 million years ago: In association
with the increasing brain size of the genus Homo, hand gestures
became fully syntactic (i.e., with syntax; with ordered
arrangements), but vocalizations also became prominent.

... ... d) 100,000 years ago: Homo sapiens switched to speech as
its primary means of communication, with gestures now playing a
secondary role.

... ... e) Modern times: The development of telecommunication now
permits the routine use of spoken language in the complete
absence of hand gestures, but even so, many people find
themselves gesturing when they speak on the telephone.

7) Concerning the question of what it was that enabled our
species to prevail over other large-brained hominids, the author
concludes: "Perhaps the most plausible answer is that they
prevailed because of superior technology. But that technology
might have resulted, not from an increase in brain size or
intelligence, but from a switch from manual to vocal language
that allowed them to use their hands for the manufacture of tools
and weapons and their voices for instruction."

American Scientist Mar-Apr 1999 87:138

Related Background:

HYPOGLOSSAL CANAL SIZE AND HOMINID SPEECH

The mammalian *hypoglossal canal transmits the *nerve that
supplies the *motor innervation to the tongue. Hypoglossal canal
size has been used to date the origin of human-like speech
capabilities to at least 400,000 years ago, and to assign modern
human vocal abilities to *Neandertals. These conclusions are
based on the hypothesis that the size of the hypoglossal canal is
indicative of speech capabilities.

D. DeGusta et al (3 authors at 2 installations, US) present the
results of a study to test the hypothesis that hypoglossal canal
size is indicative of speech. The authors report they measured
the following: a) the hypoglossal canals of 75 nonhuman primates
and 104 modern humans; b) the hypoglossal canal in specimens of
the early *hominid *taxa *Australopithecus afarensis and
*Australopithecus boisei; c) both the nerve and canal diameter
and estimated nerve axon number in a sample of human cadavers.
The authors report the following results: a) Many nonhuman
primate specimens have hypoglossal canals that are absolutely and
relatively within the size range of modern humans. b) The
hypoglossal canals of Australopithecus afarensis,
Australopithecus boisei, and *Australopithecus africanus are also
within the modern human size range. c) The size of the
hypoglossal nerve and the number of axons it contains do not
appear to be significantly correlated with the size of the
hypoglossal canal. The authors conclude: "The size of the
hypoglossal canal is not a reliable indicator of speech.
Therefore the timing of the origin of human language and the
speech capabilities of Neandertals remain open questions." [*Note
#1].

Editor's note: The authors present this report essentially as a
refutation of a paper by R.F. Kay et al, a summary of which
appears in the background material below.

Proc. Nat. Acad. Sci. 1999 96:1800

Notes:

... ... *hypoglossal canal: This canal, at the level of the
brainstem, is a passageway through bone for the XII cranial
nerve, the nerve bundle that innervates the tongue.

... ... *nerve: In general, the term "nerve" refers to a bundle
of nerve axons (nerve fibers; neuron axons), the nerve usually
visible to the naked eye. Nerves can contain large number of
individual axons: the optic nerve in humans, for example,
contains approximately 1 million nerve fibers. The hypoglossal
nerve, the cranial nerve of relevance in this report, contains
mostly nerve axons whose cell bodies are in the hypoglossal
nucleus in the brainstem (efferent fibers carrying information to
activate the muscles of the tongue), and perhaps some axons
carrying information from sensory receptors in the tongue to the
central nervous system (afferent fibers).

... ... *motor innervation: This refers to the anatomical
connections of nerve fibers to muscle cells, the electrical
activity of the nerve axons resulting in the activation of the
muscle cells.

... ... *Neandertals: (Neanderthals) About 10 kilometers east of
Dusseldorf in Germany, in the valley of the Dussel, there is a
little town called Neander. One hundred and forty-one years ago,
in the summer of 1856, some workmen broke into a cave to get at
the limestone inside and discovered a set of ancient bones. Most
of the bones were smashed to bits by the workmen, but some of the
bones, including part of the skull, survived, and the skeleton
was soon recognized by anthropologists as belonging to an ancient
race of men who came to be known as the Neanderthals. A
Neanderthal fossil had actually been discovered some years
earlier in Gibraltar, but not recognized as such. Neanderthal-
like fossils have also been found in France, Spain, Italy,
Yugoslavia, Iraq, China, Java, and Israel. For more than a
century, one of the central questions in paleoanthropology has
been whether modern man evolved from this race.

... ... *hominid: The term "hominid" refers to any primate in the
human family (Hominidae) of which Homo sapiens (modern man) is
the only living specimen.

... ... *taxa: In general, a grouping defined in terms of shared
similar characters.

... ... *Australopithecus afarensis: The first record of human
footprints, of hominids walking upright, was discovered at
Laetoli in East Africa, and has been dated at 3.6 million years
ago. This ancestor, Australopithecus afarensis, probably weighed
25 to 50 kilograms (60 to 120 lbs.) as an adult.

... ... *Australopithecus boisei: Discovered by Mary Leakey in
the Olduvai Gorge in Tanzania, this fossil has been dated at 1.75
million years ago.

... ... *Australopithecus africanus: Apparently derived from
Australopithecus afarensis were several species, including
Australopithecus africanus, a species which is believed to have
appeared approximately 3 million years ago.

 ... ... *Note #1: Although the focus in this report is on the
role of the neural innervation of the tongue in human speech, it
must be emphasized that the organization of information and motor
output necessary for speech apparently occurs concomitantly in
several localized region of the cerebral cortex, and the
evolution of these regions of the brain most likely played a
significant role in the appearance of speech in humans.
Essentially, the hypoglossal nerve merely transmits information
originating in the brain, and both the origin and transmission of
this information must be considered in any analysis of the
evolution of human speech. Unfortunately, the brain is soft
tissue and is not preserved in fossils; what we have is bone, and
the data provided by bone and relevant archeological entities.

Related Background:

ORIGIN OF HUMAN VOCAL BEHAVIOR: AN ANATOMICAL CONSIDERATION

It can be argued that language is the most important behavioral
attribute that distinguishes humans from other animals, and one
of the important problems in anthropology and human evolution is
to demarcate as narrowly as possible the time frame during which
language in humans first appeared. Such demarcations have been
based on either apparent anatomical correlates (e.g., bone and
soft tissue analysis) or apparent archeological correlates (e.g.,
analysis of apparent symbolic behavior), with no firm specific
consensus among specialists. One of the important anatomical
features related to language is the nerve supply controlling the
muscles of the tongue. The mammalian hypoglossal canal is a bony
canal that contains the trunk of nerve fibers that constitute
this nerve supply. This canal is absolutely and relatively larger
in modern humans than it is in the African apes. ... ... Kay et
al (3 authors at Duke University, US) report a study of the
cross-sectional areas of hypoglossal canals in adult skulls of
contemporary humans, African apes, and several key fossil
hominids. They propose that hypoglossal canal size in fossil
hominids may provide an indication of the motor coordination of
the tongue and reflect the evolution of speech and language. What
they report is that the hypoglossal canals of gracile
Australopithecus, and possibly Homo habilis, fall within the
range of extant African apes, and are significantly smaller than
those of modern Homo. The canals of Neanderthals and an early
"modern" Homo sapiens (Skhul 5), as well as of African and
European middle Pleistocene Homo (Kabwe and Swanscombe), fall
within the range of contemporary Homo and are significantly
larger than those of Pan troglodytes (a chimpanzee species). In
summary, the authors suggest these anatomical findings indicate
the vocal capabilities of Neanderthals were the same as those of
humans today. The authors further suggest that the vocal
abilities of Australopithecus were not advanced significantly
over those of chimpanzees, whereas those of Homo may have been
essentially modern by at least 400,000 years ago, which is
consistent with the evidence for accelerated encephalization
rates in middle Pleistocene Homo. The authors conclude: "Thus,
human vocal abilities may have appeared much earlier in time than
the first archeological evidence for symbolic behavior."

Proc. Nat. Acad. Sci. 1998 95:5417

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4. ON THE ACQUISITION OF LANGUAGE BY CHILDREN

J.R. Saffran et al (University of Wisconsin Madison, US) discuss
the acquisition of language by children, the authors making the
following points:

1) Before infants can begin to map words onto objects in the
world, they must determine which sound sequences are words. To do
so, infants must uncover at least some of the units that belong
to their native language from a largely continuous stream of
sounds in which words are seldom surrounded by pauses. Despite
the difficulty of this reverse-engineering problem, infants
successfully segment words from fluent speech from approximately
7 months of age.

2) How do infants learn the units of their native language so
rapidly? One fruitful approach to answering this question has
been to present infants with miniature artificial languages that
embody specific aspects of natural language structure. Once an
infant has been familiarized with a sample of this language, a
new sample, or a sample from a different language, is presented
to the infant. Subtle measures of surprise (e.g., duration of
looking toward the new sounds) are then used to assess whether
the infant perceives the new sample as more of the same or
something different. In this fashion, we can ask what the infant
extracted from the artificial language, which can lead to
insights regarding the learning mechanisms underlying the
earliest stages of language acquisition.

3) Syllables that are part of the same word tend to follow one
another predictably, whereas syllables that span word boundaries
do not. In a series of experiments, it has been found that
infants can detect and use the statistical properties of syllable
co-occurrence to segment novel words. More specifically, infants
do not detect merely how frequently syllable pairs occur, but
rather the probabilities with which one syllable predicts
another. Thus, infants may find word boundaries by detecting
syllable pairs with low transitional probabilities. What makes
this finding astonishing is that infants as young as 8 months
begin to perform these computations with as little as 2 minutes
of exposure. By soaking up the statistical regularities of
seemingly meaningless acoustic events, infants are able to
rapidly structure linguistic input into relevant and ultimately
meaningful units.

Proc. Nat. Acad. Sci. 2001 98:12874

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5. ON THE CRITICAL PERIOD HYPOTHESIS OF LANGUAGE ACQUISITION.

A.D. Friederici et al (Max Planck Institute of Cognitive
Neuroscience Leipzig, DE) discuss language acquisition, the
authors making the following points:

1) The acquisition of certain basic cognitive functions seems to
depend on appropriate input during so-called critical periods (1,
2). Rare cases of children who grew up without language input
during their first years demonstrate that perfect mastery of a
language cannot be acquired in later periods (3). It has been
suggested that second language learning is subject to similar
restrictions (4, 5). Although the age of exposure during language
acquisition seems to have a dramatic impact on the subsequent
real-time processing of sentences, the mechanisms underlying this
critical-period effect remain unclear. Although some researchers
assume that the critical period effect can be explained by the
earlier-is-better hypothesis (e.g., refs. 1 and 3), which holds
that maturational constraints determine language learning, others
assume the less-is-more hypothesis, which claims that differences
in early and late language learning are a by-product of
children's processing capacity limitations, providing a more
focused approach to the language input.

2) The employment of brain imaging and electrophysiological
techniques has shed light on the neural bases of the well
established behavioral differences between first (L1) and second
language (L2) acquisition. Lexical-semantic processing of word
meanings is relatively similar for native speakers and L2
learners. In contrast, syntactic real-time analyses of a
sentence's grammatical information seem to differ considerably
for late learners versus native speakers. In native speakers,
severe syntactic violations elicit a characteristic biphasic
response in the event-related brain potential consisting of an
early negativity and a late positivity. This early negativity was
found often with a left anterior maximum but sometimes with a
more bilateral frontocentral distribution. The factor determining
this variation, however, has not yet been identified.

3) The authors report that by using event-related brain
potentials, we demonstrate that adults who learned a miniature
artificial language display a similar real-time pattern of brain
activation when processing this language as native speakers do
when processing natural languages. Participants trained in the
artificial language showed two event-related brain potential
components taken to reflect early automatic and late controlled
syntactic processes, whereas untrained participants did not. The
authors suggest this result challenges the common view that late
second language learners process language in a principally
different way from native speakers. The suggest their findings
demonstrate that a small system of grammatical rules can be
syntactically instantiated by the adult speaker in a way that
strongly resembles native-speaker sentence processing.

References (abridged):

1. Lenneberg, E. H. (1976) Biological Foundations of Language
(Wiley, New York).

2. Hubel, D. H. & Wiesel, T. N. (1977) Proc. R. Soc. London 198,
1-59.

3. Curtiss, S. (1977) Genie: A Psycholinguistic Study of a
Modern-Day Wild Child (Academic, New York).

4. Johnson, J. S. & Newport, E. L. (1989) Cognit. Psychol. 21,
60-99.

5. Harley, B. & Wang, W. (1997) in Tutorials in Bilingualism:
Psycholinguistic Perspectives, eds. de Groot, A. M. B. & Kroll,
J. F. (Lawrence Erlbaum Associates, Mahwah, NJ), pp. 19-51.

Proc. Nat. Acad. Sci. 2002 99:529

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6. ON THE NEUROBIOLOGY OF COGNITION.

M.J. Nichols and W. T. Newsome (Stanford University, US) discuss
the neurobiology of cognition, the authors making the following
points:

1) It is astounding that cognition and emotion -- phenomena that
cannot be duplicated in our most sophisticated computers -- arise
naturally from the electrical activity of large systems of
neurons within the brain. Scientific investigation of these
phenomena is inherently interdisciplinary, drawing strength from
fields as diverse as neurophysiology, cognitive psychology and
computational theory. Exciting new findings have emerged in
recent decades concerning the neural underpinnings of cognitive
functions such as perception, learning, memory, attention,
decision-making, language and motor planning, as well as the
influence of emotion and motivation upon cognition. With very few
exceptions, however, our understanding of these phenomena remains
rudimentary. We can identify particular locations in the brain
where neuronal activity is modulated in concert with particular
external or internal stimuli. In some cases we can even
artificially manipulate neural activity in a specific brain
structure (using electrical or pharmacological techniques) and
cause predictable changes in behaviour. But we encounter
substantial difficulties in understanding how modulations in
neural activity at one point in the nervous system are actually
produced by synaptic interactions between neural systems. Thus
our current state of knowledge is somewhat akin to looking out
the window of an airplane at night. We can see patches of light
from cities and towns scattered across the landscape, we know
that roads, railways and telephone wires connect those cities,
but we gain little sense of the social, political and economic
interactions within and between cities that define a functioning
society.

2) To achieve a more sophisticated level of understanding,
investigators must develop new experimental techniques for
studying functional interactions between neurons and systems of
neurons, and new models for understanding the behavior of
complex, dynamic systems like the brain. Whether major
breakthroughs occur on the timescale of years or decades depends
substantially on success in developing these new techniques.
Irrespective of timescale, an increasingly sophisticated
understanding of the neural basis of cognition will influence our
society profoundly. It will have practical applications such as
treatment of mental disease and the design of intelligent
machines, and will raise contentious social issues such as the
freedom of each individual to choose their behaviour, and the
extent to which society can reasonably demand individual
responsibility for behaviour.

3) Understanding the neural basis of a specific cognitive
function typically begins with behavioral observations and
hypotheses developed by perceptual and cognitive psychologists.
Equipped with sound conceptual frameworks originating in
behavior, neurophysiologists can then study underlying brain
function at several levels. At the coarsest level, the primary
issue is "localization" of function: identifying, for example,
neural systems in the brain that are strongly active in response
to visual images or when spatial attention is deployed to
different regions of a visual scene. Localization of function has
been a dominant theme in brain science, beginning in the
nineteenth century when "phrenologists" attempted to map mental
functions onto the brain by correlating aspects of personality
and mental ability with the sizes of bumps at different locations
on the skull. More reliable evidence for localization of function
emerged in the early part of the twentieth century as
neurologists learned to recognize mental deficits (sometimes
highly specific) that occurred subsequent to damage in particular
regions of the brain.

4) The most commonly used techniques in modern studies of
localization are positron emission tomography (PET) and
functional magnetic resonance imaging (fMRI), which generate most
of the glossy figures in popular science magazines that depict
mental activity as colored blobs on a picture of the brain. Both
PET and fMRI measure changes in blood flow to specific regions of
the brain while human subjects perform various cognitive
tasks(1). The blood flow signal is assumed to reflect changes in
metabolic demand resulting from altered levels of neural
activity. Using PET and fMRI, investigators can study brain
activity in humans at the spatial scale of individual brain
structures (a few millimetres) and on a timescale of a few
seconds(2-5).

References (abridged):

1. Ogawa, S. et al. Proc. Natl Acad. Sci. USA 89, 5951-5955
(1992).

2. Posner, M. I. & Raichle, M. E. Proc. Natl Acad. Sci. USA 95,
763-764 (1998).

3. Sell, L. A. et al. Eur. J. Neurosci. 11, 1042-1048 (1999).

4. Wandell, B. A. Annu. Rev. Neurosci. 22, 145-173 (1999).

5. Hubel, D. H. Eye, Brain, and Vision (Scientific American
Library, New York, 1995).

Nature 1999 402:C35

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7. LANGUAGE DISCRIMINATION BY HUMAN NEWBORNS AND BY COTTON-TOP
TAMARIN MONKEYS.

F. Ramus et al (CNRS Paris, FR) discuss language in human
newborns, the authors making the following points:

1) A fundamental question in the study of language evolution and
acquisition is the extent to which humans are innately endowed
with specialized capacities to comprehend and produce speech.
Theoretical arguments have been used to argue that language
acquisition must be based on an innately specified language
faculty (1,2), but the precise nature and extent of this
"language organ" is mainly an empirical matter, which notably
requires studies of human newborns as well as nonhuman animals
(3-5). With respect to studies of humans, we already know that
newborns as young as 4 days old have the capacity to discriminate
phonemes categorically and perceive well-formed syllables as
units; they are sensitive to the rhythm of speech, as shown in
experiments in which newborns distinguish sentences from
languages that have different rhythmic properties but not from
languages that share the same rhythmic structure; however,
newborns do not discriminate languages when speech is played
backward, and neurophysiological studies suggest that both
infants and adults process natural speech differently from
backward speech. All these studies indicate that humans are born
with capacities that facilitate language acquisition and that
seem well attuned to the properties of speech. Studies of
nonhuman animals, however, show that some of these capacities may
predate our hominid origins. For example, insects, birds,
nonprimate mammals, and primates process their own, species-
typical sounds in a categorical manner, and some of these species
perceive speech categorically.

2) The authors report a study whose aim was to extend the
comparative study of speech perception in three directions.
First, using the same design and the same material, the authors
have conducted joint experiments on human newborns and on
monkeys. Second, whereas most studies of nonhuman animal speech
perception involve extensive training before testing on a
generalization task, experimental approach of the authors -- the
habituation-dishabituation paradigm -- involves no training and
parallels the method used in studies of infant speech perception.
Thus, conditions are met to appropriately compare the two
populations. Third, most studies of speech processing in animals
involve tests of phonemic perception. The authors extend the
analysis to sentence perception, thereby setting up a much
broader range of perceptual problems.

3) In summary: Humans, but no other animal, make meaningful use
of spoken language. What is unclear, however, is whether this
capacity depends on a unique constellation of perceptual and
neurobiological mechanisms or whether a subset of such mechanisms
is shared with other organisms. To explore this problem, parallel
experiments were conducted on human newborns and cotton-top
tamarin monkeys to assess their ability to discriminate
unfamiliar languages. A habituation-dishabituation procedure was
used to show that human newborns and tamarins can discriminate
sentences from Dutch and Japanese but not if the sentences are
played backward. Moreover, the cues for discrimination are not
present in backward speech. This suggests that the human
newborns' tuning to certain properties of speech relies on
general processes of the primate auditory system.

References (abridged):

1. N. Chomsky, Language and Problems of Knowledge (MIT Press,
Cambridge, MA, 1988).

2. S. Pinker, The Language Instinct (William, Morrow, and Co.,
New York, 1994).

3. A. Doupe and P. Kuhl, Annu. Rev. Neurosci. 22, 567 (1999).

4. A. Ghazanfar and M. D. Hauser, Trends Cogn. Sci. 3, 377
(1999).

5. E. S. Spelke and E. L. Newport, in Handbook of Child
Psychology, Volume 1: Theoretical Models of Human Development, R.
M. Lerner, Ed. (Wiley, New York, 1998), pp. 275-340.

Science 2000 288:349

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8. AN INNATE BASIS FOR LANGUAGE?

Dorothy V. Bishop (University of Oxford, UK) discusses language
acquisition, the author making the following points:

1) "It is an established opinion amongst some men, that there are
in the understanding certain innate principles; some primary
notions, characters, as it were stamped upon the mind of man:
which the soul receives in its very first being, and brings into
the world with it. It would be sufficient to convince
unprejudiced readers of the falseness of this supposition, if I
should only show... how men...may attain to all the knowledge
they have, without the help of any innate impressions; and may
arrive at certainty, without any such original notions or
principles..." Some 300 years after the British philosopher John
Locke (1632-1704) wrote these words in his _Essay Concerning
Human Understanding_, there is still a lively debate about how
much "innate" linguistic knowledge an infant is born with.

2) We know from patients with neurological impairments and from
neuroimaging studies that the adult brain is a modular system,
that is, different regions perform specific functions. But how
does the brain get that way? One view is that distinct brain
regions govern particular functions -- such as, the processing of
language or numbers -- from the outset, a notion in keeping with
the idea of innate principles. An alternative view is that the
embryonic brain is not specialized and that the emergence of
distinct brain regions governing particular functions becomes
apparent only during postnatal development. Locke's antipathy to
"innate principles" appears vindicated by research showing that
modularity (distinct brain regions governing particular
functions) is a property that emerges during postnatal
development and is dependent on both biological maturation and
interactions with the environment.

3) There is, however, a persistent fly buzzing around in the
ointment of the emergent modularity theory. Williams syndrome is
a genetic disorder in which complex language skills can develop
despite general mental deficits. This syndrome differs from
specific language impairment, in which language acquisition is
selectively impaired but development is otherwise normal. To
explain this pattern of dissociation, it has been argued that the
brain must have an innate language module that is selectively
impaired in specific language impairment but is spared in
Williams syndrome. Paterson and colleagues (1) have presented
data that question this interpretation. They argue that cognitive
profiles of very young children with Williams syndrome look
different from those reported in older children and adults with
the disorder. Their study breaks new ground by applying state-of-
the-art methods that use the preferential looking test (in which
the tester infers, for example, whether infants understand a word
by measuring the time they spend looking at a named object
compared to that for a distracting object) to measure cognitive
abilities. On a vocabulary recognition test, toddlers with
Williams syndrome did worse than age-matched controls, and no
better than toddlers with Down syndrome, who have a similar IQ.
However, on a test of number skills, toddlers with Williams
syndrome did well, outperforming those with Down syndrome. It is
well established that adult patients with Williams syndrome do
better (relatively speaking) on language tasks than on those
involving numbers. So, the message from recent work seems simple:
Just because a person with congenital brain impairment shows an
uneven intellectual profile, one cannot assume that this profile
has been present from birth (2-5).

References (abridged):

1. S. J. Paterson et al., Science 286, 2355 (1999).

2. C. B. Mervis and B. F. Robinson: Dev. Neuropsychol. 2000
17:111.

3. B. P. Klein and C. B. Mervis, Dev. Neuropsychol. 16, 177
(1999).

4. P. Howlin et al., J. Appl. Res. Intellect. Disabil. 11, 207
(1998).

5. C. B. Mervis et al., in Neurodevelopmental Disorders, H.
Tager-Flusberg, Ed. (MIT Press, Cambridge, MA, 1999), pp. 65-110.

Science 1999 286:2283

Related Background:

ON MODULAR COGNITIVE SYSTEMS IN THE HUMAN BRAIN

One of the central challenges of cognitive neuroscience is to
unmask the apparent unitary nature of perceptual, memorial, and
cognitive systems. Neuropsychological analyses, functional brain-
imaging methods, and analyses of normal reaction times have
revealed that apparently unitary processes consist of multiple
components. Frequently, these multiple components are distributed
across the cerebral hemispheres, but appear unified because of
the integration possible via the corpus callosum.

K. Baynes et al (4 authors at 3 installations, US) report a case
of elective surgery for a severe epileptic disorder, the surgery
involving a resection of the corpus callosum in a left-handed
woman with left-hemisphere dominance for spoken language. The
patient demonstrated a dissociation between spoken and written
language. Words flashed to the dominant left hemisphere were
easily spoken out loud, but could not be written. When words were
flashed to the patient's right hemisphere, she could not speak
them out loud but she could write them with her left hand. The
authors suggest this marked dissociation supports the view that
spoken and written language output can be controlled by
independent hemispheres, even if before hemispheric disconnection
spoken and written language appear as inseparable cognitive
entities.

Science 1998 280:902

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9. LANGUAGE-RELATED CORTEX IN DEAF INDIVIDUALS: FUNCTIONAL
SPECIALIZATION FOR LANGUAGE OR PERCEPTUAL PLASTICITY?

David Caplan (Massachusetts General Hospital Boston, US)
discusses functional specialization, the author making the
following points:

1) Petitto et al. (1) report a positron emission tomography (PET)
study of the regions of the brain that increase their regional
cerebral blood flow when individuals process signed language. The
essence of their results is that, in 11 profoundly deaf subjects,
regional cerebral blood flow responses to a series of tasks
involving signed language occurred in the same areas of the brain
in which responses to similar tasks occur in hearing subjects
processing spoken language. These brain regions are the auditory
association cortex adjacent to the primary auditory koniocortex
and the left inferior frontal cortex. Traditional views of the
functional role of these areas, going back over 125 years and
still widely accepted, maintain that the first of these areas is
involved in speech perception and second in planning speech
production. The results reported by Petitto et al. provide a
quite different view of these brain regions -- one that sees them
as being involved in processing language, regardless of the
modality in which it is presented.

2) The results of Petitto et al. are not totally unexpected. Both
studies of the effects of stroke and previous studies using
functional neuroimaging have shown considerable overlap between
regions of the brain involved in processing spoken and signed
language. The pioneering studies of congenitally deaf stroke
victims carried out by Bellugi and her colleagues (2,3) showed
that left but not right hemisphere strokes in the perisylvian
area produced aphasia in these patients, whereas right-sided
lesions produced nonlinguistic visuospatial deficits. This, of
course, is the usual pattern of effects of lesions seen in
hearing individuals using spoken language. A particularly
convincing finding was that deaf patients with left hemisphere
strokes could not use space to establish the linguistic function
of co-reference (relating the signed equivalent of a pronoun to a
noun) but could use space for other manual tasks. Activation
studies by Neville and her colleagues using functional magnetic
resonance imaging (fMRI) showed that both deaf and hearing native
signers activated left hemisphere "language" areas when viewing
sentences in American Sign Language (ASL) (4).

3) The paper of Petitto et al. (1) reinforces the view that the
functions carried out in what is widely thought of as auditory
association cortex need to be reconsidered. The careful
anatomical analyses and narrowly designed experimental contrasts
used in this study leave little doubt that this brain region can
respond to visually presented elementary linguistic stimuli in
individuals deprived of auditory stimulation who use signed
language. Whether this is because this region supports language
or because it supports high-level visual temporal processing is a
fundamental question about the neural basis of language that
remains to be answered (5).

References (abridged):

1. Petitto, L. A. , Zatorre, R. J. , Gauna, K. , Nikelski, E. J.
, Dostie, D. & Evans, A. C. (2000) Proc. Natl. Acad. Sci. USA 97,
13961-13966.

2. Bellugi, U. , Poizner, H. & Klima, E. S. (1989) Trends
Neurosci. 12, 380-388.

3. Hickok, G. , Bellugi, U. & Klima, E. S. (1998) Trends Cognit.
Sci. 2, 129-136.

4.  Neville, H. J. , Bavelier, D. , Corina, D. , Rauschecker, J.
, Karni, A. , Lalwani, A. , Braun, A. , Clark, V. , Jezzard, P. &
Turner, R. (1998) Proc. Natl. Acad. Sci. USA 95, 922-929.

5. Soderfeldt, B. , Ingvar, M. , Ronnberg, J. , Eriksson, L. ,
Serrander, M. & Stone-Elander, S. (1997) Neurology 49, 82-87.

Proc. Nat. Acad. Sci. 2000 97:13476

Related Background Brief:

SPEECH-LIKE CEREBRAL ACTIVITY IN PROFOUNDLY DEAF PEOPLE
PROCESSING SIGNED LANGUAGES: IMPLICATIONS FOR THE NEURAL BASIS OF
HUMAN LANGUAGE. For more than a century we have understood that
our brain's left hemisphere is the primary site for processing
language, yet why this is so has remained more elusive. Using
positron emission tomography, the authors report cerebral blood
flow activity in profoundly deaf signers processing specific
aspects of sign language in key brain sites widely assumed to be
unimodal speech or sound processing areas: the left inferior
frontal cortex when signers produced meaningful signs, and the
planum temporale bilaterally when they viewed signs or
meaningless parts of signs (sign-phonetic and syllabic units).
Contrary to prevailing wisdom, the planum temporale may not be
exclusively dedicated to processing speech sounds, but may be
specialized for processing more abstract properties essential to
language that can engage multiple modalities. The authors
hypothesize that the neural tissue involved in language
processing may not be prespecified exclusively by sensory
modality (such as sound) but may entail polymodal neural tissue
that has evolved unique sensitivity to aspects of the patterning
of natural language. Such neural specialization for aspects of
language patterning appears to be neurally unmodifiable in so far
as languages with radically different sensory modalities such as
speech and sign are processed at similar brain sites, while, at
the same time, the neural pathways for expressing and perceiving
natural language appear to be neurally highly modifiable. L.A.
Petitto et al: 2000 97:13961.

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10. OLD VS. NEW VIEWS OF LANGUAGE ACQUISITION.

Patricia K. Kuhl (University of Washington, US) discusses
theories of language acquisition, the author making the following
points:

1) In the last half of the 20th century, debate on the origins of
language was ignited by a highly publicized exchange between a
strong nativist and a strong learning theorist. In 1957, the
behavioral psychologist B F. Skinner (1904-1990) proposed a
learning view in his book _Verbal Behavior_, arguing that
language, like all animal behavior, was an "operant" that
developed in children as a function of external reinforcement and
shaping (1). By Skinner's account, infants learn language as a
rat learns to press a bar through the monitoring and management
of reward contingencies. Noam Chomsky, in a review of Verbal
Behavior, took a very different theoretical position (2,3).
Chomsky argued that traditional reinforcement learning had little
to do with humans ability to acquire language. He posited a
"language faculty" that included innately specified constraints
on the possible forms human language could take. Chomsky argued
that the innate constraints of infants for language included
specification of a universal grammar and universal phonetics.
Language was one of the primary examples of what Fodor called a
module -- domain-specific, informationally encapsulated, and
innate (4).

2) The two approaches took strikingly different positions on all
of the critical components of a theory of language acquisition:
(i) the initial state of knowledge, (ii) the mechanisms
responsible for developmental change, and (iii) the role played
by ambient language input. On Skinner's view, no innate
information was necessary, developmental change was brought about
through reward contingencies, and language input did not cause
language to emerge. On Chomsky's view, infants' innate knowledge
of language was a core tenet, development constituted "growth" or
maturation of the language module, and language input triggered
(or set the parameters for) a particular pattern from among those
innately provided.

3) A great deal has been learned since the debate ensued, caused
largely by experiments conducted on infants. Infants' perception
of the phonetic units of speech, which requires tracking the
formant frequencies (5), and their detection of words from cues
in running speech, support a different view. The emerging view
argues that the kind of learning taking place in early language
acquisition cannot be accounted for by Skinnerian reinforcement.
On the other hand, the idea that language acquisition involves a
selectionist process wherein language input operates on innately
specified options also is not supported. The emerging view
suggests that infants engage in a new kind of learning in which
language input is mapped in detail by the infant brain.

4) Taken together, new analysis and principles suggest that what
is innate regarding language is not a universal grammar and
phonetics, but innate biases and strategies that place
constraints on perception and learning. They allow infants to
recover from language input the rules by which people in their
community communicate. Language is thus innately discoverable,
but not innate in the way that selectionist models suggested. The
learning strategies used by infants may themselves have
influenced the nature of language, in much the same way that
general auditory processing influenced the selection of phonetic
units for language during its evolution. The continued study of
language development by infants promises to reveal the precise
nature of the relationship between language and mind.

References (abridged):

1.  Skinner, B. F. (1957) Verbal Behavior (Appleton-Century-
Crofts, New York).

2.  Chomsky, N. (1957) Language 35, 26-58.

3. Wexler, K. & Culicover, P. W. (1980) Formal Principles of
Language Acquisition (MIT Press, Cambridge, MA).

4.  Fodor, J. A. (1983) The Modularity of Mind: An Essay on
Faculty Psychology (MIT Press, Cambridge, MA).

5.  Stevens, K. N. (1998) Acoustic Phonetics (MIT Press,
Cambridge, MA).

Proc. Nat. Acad. Sci. 2000 97:11850

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11. MIRROR NEURONS AND LANGUAGE ACQUISITION.

H. Th‚oret and A. Pascual-Leone (Harvard University, US) discuss
mirror neurons, the authors making the following points:

1) The study of how we understand the meaning of actions
performed by others has seen a resurgence in the last few years,
triggered in part by the discovery of a population of neurons
that becomes active both when a monkey executes a specific action
and when it sees another individual make a similar movement [1
3]. The existence of these so-called "mirror" neurons has given
credence to the direct-matching hypothesis, which stipulates that
actions are understood because observation of an action activates
the same neural circuitry required to perform that action. For
example, a single cell that discharges when a monkey grasps an
object with its fingers would also discharge when it sees another
monkey picking up a small fruit. The monkey would then recognize
that specific movement because it mapped the observed action onto
its own neural motor representation. The existence of mirror
neurons in humans was recently suggested by transcranial magnetic
stimulation (TMS) and brain imaging studies, which showed that
the observation of complex actions induces changes in motor
cortex excitability [4 5] and activates brain areas involved in
the generation of observed movements.

2) It has been proposed that imitation abilities in humans
evolved out of the mirror system. A recent study [Kohler et al
(2002)] has provided support for an involvement of mirror neurons
in the acquisition of language, even without the requirement of
visual input. Kohler et al recorded single units in the monkey
premotor cortex (area F5) and found a population of neurons that
discharge when the monkeys perform, see, or hear the same action.
These "audiovisual" mirror neurons can show exquisite
selectivity. For example, the authors describe a cell that
discharged when a monkey broke a peanut, saw an experimenter
break a peanut or heard a peanut being broken out of view.
However, observation of similar actions, or exposure to their
associated sounds, did not modulate the firing rate of this
neuron. These observations within individual cells were confirmed
in a population analysis, where it was shown that neurons could
discriminate between different action sounds. Furthermore, the
specific action-related sounds associated with a given neuron
elicited the strongest responses during the observation and
execution of that preferred action.

3) These data have important implications, not only for
understanding actions, but also because of the insights they
provide into how language may develop in humans. Area F5, where
audiovisual mirror neurons are located, is the monkey homologue
of human motor speech area BA44 (Broca's area), and imaging data
in humans have revealed the presence of an observation execution
matching system within Broca's area [7]. So, in addition to
strongly suggesting the involvement of mirror cells in imitation
and action understanding, the new data of Kohler et al indicate
that the human premotor mirror neuron system may very well be
involved in the imitation and acquisition of speech.

References (abridged):

1. di Pellegrino G., Fadiga L., Fogassi L., Gallese V. and
Rizzolatti G. (1992) Understanding motor events: a
neurophysiological study. Exp. Brain Res., 91:176-180.

2. Gallese V., Fadiga L., Fogassi L. and Rizzolatti G. (1996)
Action recognition in the premotor cortex. Brain, 119:593-609.

3. Rizzolatti G., Fadiga L., Gallese V. and Fogassi L. (1996)
Premotor cortex and the recognition of motor actions. Cognit.
Brain Res., 3:131-141.

4. Fadiga L., Fogassi L., Pavesi G. and Rizzolatti G. (1995)
Motor facilitation during action observation: a magnetic
stimulation study. J. Neurophysiol., 73:2608-2611.

5. Strafella A.P. and Paus T. (2000) Modulation of cortical
excitability during action observation: a transcranial magnetic
stimulation study. Neuroreport, 11:2289-2292.

Current Biology 2002 12:R736

Related Background Brief:

SPEECH LISTENING SPECIFICALLY MODULATES THE EXCITABILITY OF
TONGUE MUSCLES: A TMS STUDY. The precise neural mechanisms
underlying speech perception are still to a large extent unknown.
The most accepted view is that speech perception depends on
auditory-cognitive mechanisms specifically devoted to the
analysis of speech sounds. An alternative view is that, crucial
for speech perception, it is the activation of the articulatory
(motor) gestures that generate these sounds. The listener
understands the speaker when his/her articulatory gestures are
activated (motor theory of speech perception). By using
transcranial magnetic stimulation (TMS), the authors demonstrate
that during speech listening there is an increase of motor-evoked
potentials recorded from the listeners' tongue muscles when the
presented words strongly involve, when pronounced, tongue
movements. The authors suggest that although these data do not
prove the motor theory of speech perception, they demonstrate for
the first time that word listening produces a phoneme specific
activation of speech motor centres. L. Fadiga et al: Eur J
Neurosci 2002 15:399.

Related Background Brief:

SPEECH-INDUCED CHANGES IN CORTICOSPINAL EXCITABILITY. The authors
report experiments whose aim was to investigate the effects of
speech on the excitability of corticospinal pathways to human
hand muscles. Single transcranial magnetic stimuli were given
randomly over the hand area of either the left or right motor
cortex of 10 right-handed and 3 left-handed normal volunteers.
Electromyographic responses were recorded in the relaxed first
dorsal interosseous muscle while the subjects (a) read aloud a
piece of text, (b) read silently, (c) spoke spontaneously, or (d)
made sounds without speaking. The only consistent effect across
subjects occurred during task a, which significantly increased
the size of responses evoked in the dominant hand of all
subjects, but had either no effect (8 subjects) or a smaller
effect in the nondominant hand. Tasks b and d had no reliable
effect, whereas task c tended to increase response size in both
hands. Control measurements suggest that the effects in task a
were caused by changes in cortical rather than spinal
excitability. The authors suggest this is the first demonstration
of lateralized speech effects on the excitability of cortical arm
areas. The authors suggest the results provide a useful adjunct
to other tests of cerebral dominance, using only single- rather
than repetitive-pulse cortical stimulation. H. Tokimura et al:
Ann Neurol 1996 40:628.

Related Background Brief:

IMITATION, MIRROR NEURONS AND AUTISM. Various deficits in the
cognitive functioning of people with autism have been documented
in recent years but these provide only partial explanations for
the condition. The authors focus instead on an imitative
disturbance involving difficulties both in copying actions and in
inhibiting more stereotyped mimicking, such as echolalia. A
candidate for the neural basis of this disturbance may be found
in a recently discovered class of neurons in frontal cortex,
"mirror neurons" (MNs). These neurons show activity in relation
both to specific actions performed by self and matching actions
performed by others, providing a potential bridge between minds.
MN systems exist in primates without imitative and "theory of
mind" abilities and the authors suggest that in order for them to
have become utilized to perform social cognitive functions,
sophisticated cortical neuronal systems have evolved in which MNs
function as key elements. Early developmental failures of MN
systems are likely to result in a consequent cascade of
developmental impairments characterised by the clinical syndrome
of autism. J.H. Williams et al: Neurosci Biobehav Rev 2001
25:287.

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12. GRAMMAR, LANGUAGE, AND WORDS.

Massimo Piatelli-Palmarini (University of Arizona, US) discusses
grammar vs. language, the author making the following points:

1) Two styles of explaining the science of mind and behavior have
been competing for as long as anyone cares to remember:
empiricist, centering on habit formation, statistical learning,
imitation and association; and rationalist, focusing on the
projection of internally represented rules. Despite relentless
effort, the former has delivered rather meager results, whereas
the latter, with its pivotal concept of an internally represented
grammar, has produced the solid "conceptual cognitive
revolution".

2) For a rationalist cognitive scientist, a grammar is a finite
mental object, systematically assigning abstract structures to
all the well-formed expressions of a language -- that is, to each
member of a set that, for natural languages (such as Chinese or
Italian), is infinite and discrete. Infinite, because every
speaker of a language can produce and understand an unlimited
number of new grammatical sentences. Discrete, because continuous
modification of a sentence to change it into another is
impossible. No sentence could be halfway between "It's a good
car, but they don't sell it" and "It's a good car, but they don't
tell it."

3) A grammar capable of generating complex structures for all
well-formed sentences of a natural language must have recursive
rules, because phrasal constituents can contain other phrasal
constituents of the same or higher kinds ("The young doctor's
three beautiful sisters" is a noun phrase containing another noun
phrase; "The spy who came in from the cold" is a noun phrase
containing a sentence). Moreover, structural rules of sentence
formation can be applied recursively to embed relative clauses
embedding other relative clauses, without limit (as in "This is
the cat that killed the rat that ate the malt that lay in the
house that Jack built"). Because such grammars are finite,
whereas the languages they generate are infinite and contingently
shaped by use, it is advantageous, and methodologically cogent,
to consider the concept of grammar as primary, and that of
language as derived.

4) Since the mid-1950s, powerful formal criteria, derived from
analysis of the artificial languages of mathematics and computer
programming, have been applied to the study of natural languages
to determine principles by which a given class of grammars can
generate a given target language. A universal ('Chomsky')
hierarchy of grammars (automata) was established: the most
powerful class contains as a subclass the immediately less
powerful one, and so on. In tune with the dominant empiricist
inductivist tradition of the 1950s, the first grammars to be
explored at the lowest level in the hierarchy were probabilistic
and finite-state. From a very large corpus of ascertained
utterances of the language, one can compute the conditional
probability that a word (or string of words) will follow another.

References:

1. Wasow, T. in Foundations of Cognitive Science (ed. Posner, M.)
161 205 (MIT Press, Cambridge, Massachusetts, 1991)

2. Chomsky, N. The Minimalist Program (MIT Press, Cambridge,
Massachusetts, 1995)

3. Pullum, G. K. & Scholtz, B. C. Nature 413, 367 (2001) Nature
2002 416:129

Related Background Brief:

MORE THAN WORDS.

"In the popular view, a language is merely a fixed stock of
words. Purists worry about foreign loanwords; conservatives decry
slang; and groundless claims that there are hundreds of Eskimo
words for snow are constantly made in popular writing, as if
nothing matters about languages but their lexicons. But the
popular view cannot be right, because (as linguist Paul Postal
has observed) membership in the word stock of a natural language
is open. Consider this example: "GM's new Zabundra makes even the
massive Ford Expedition look economical." If English had an
antecedently given set of words, then this expression would not
be an English sentence at all, because 'Zabundra' is not a word
(we just invented it). Yet the sentence is not just grammatical
English, it is readily interpretable (it clearly implies that the
Zabundra is a large, fuel-hungry sports utility vehicle produced
by General Motors). Similar points could be made regarding word
borrowing, personal names, scientific nomenclature,
onomatopoeisis, acronyms, loaned words, and so on; English is not
a fixed set of words. A more fundamental reason that a language
cannot just be a word stock is that expressions have syntactic
structure. For example, in most languages, the order of words can
be significant: 'Mohammed will come to the mountain' contains the
same words as 'The mountain will come to Mohammed', but the
expressions are very different."

Geoffrey K. Pullum: Nature 2001 413:367.

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