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Review of  Language Development and Age

Reviewer: Matthew T. Carlson
Book Title: Language Development and Age
Book Author: Julia Rogers Herschensohn
Publisher: Cambridge University Press
Linguistic Field(s): Language Acquisition
Book Announcement: 19.2335

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AUTHOR: Herschensohn, Julia
TITLE: Language Development and Age
PUBLISHER: Cambridge University Press
YEAR: 2007

Matthew T. Carlson, Department of Psychology, University of Chicago

This book provides a detailed evaluation of the question of a biological
critical period (CP) for both first (L1A) and second (L2A) language acquisition,
with the primary goal of assessing the existence of such a CP for either of
these processes. Given this rather straightforward goal, Herschensohn takes
great care to provide a very precise definition of a strictly biological
(maturational) CP, and in so doing produces a complex framework for
differentiating CP effects from other kinds of age-related changes in the human
ability to acquire language. Consistent with this nuanced approach, the book
takes a broad perspective on language acquisition that incorporates theories of
Universal Grammar (UG), language processing, experience of language, social
factors, individual differences, and neural architecture and development. The
need for such a complex approach is well-motivated, and these diverse areas of
research and theory are well integrated given the constraints of space in this
volume. The book is thus well-suited for an audience with some background
knowledge in at least some of these areas interested in the effects of age on
language acquisition. Readers with particular interest in one area will find
that area placed usefully in a broader context. Although the book is couched in
terms of a binary question regarding the existence of a biological CP, asking
the question separately for L1A and L2A, the result goes beyond simple binary
distinctions to open the way for further research on the impact of particular
age-related factors on specific facets of language acquisition.

Following an introductory chapter, two chapters each are dedicated to L1A and
L2A, first describing the general process of acquisition (Chapters 2 and 4) and
then considering the influence of age on each process, respectively (Chapters 3
and 5). The final two chapters amplify the discussion of the linguistic, social,
and neurological factors in play and consider the role of age from the varied
perspectives presented in the book.

The first chapter lays out the central themes and questions to be addressed in
the book, and sets the theoretical context for the discussion. Herschensohn
previews the structure of the analyses to come, briefly contrasting the
influence of age of acquisition (AoA) on L1A and L2A, introducing the
distinction between maturational and experiential factors, and describing how
L1A and L2A can be (ethically) investigated. The following section reviews the
history of critical period research from the early studies on various nonhuman
species, amply discusses the work on birdsong, considered of particular
relevance to human language research, and motivates the criteria to be used for
judging the evidence regarding language acquisition. These criteria encompass a
distinct onset and terminus, relationships to both an intrinsic maturational
event and an extrinsic trigger, and effects on a particular system in the
organism (pp. 10-12). Crucially, critical periods are seen as a subset of
sensitive periods in that critical periods are associated with irreversible
changes in brain function (Knudsen 2004), where sensitive periods may be
associated with less dramatic changes in ability due to maturation.

After laying this groundwork, the subsequent section on language and the brain
reviews the history of critical period research on language since Lenneberg's
(1967) influential hypothesis, and sketches out evidence for the localization of
language functions in the brain and changes in brain plasticity associated with
age, relying mainly on evidence from brain damage. The final section of Chapter
1 frames the discussion in terms of the ''nature-nurture'' debate by outlining
'associationist' and 'modularist' views of human language acquisition, with the
former focusing on the role of the environment and the latter on innate
predispositions. Herschensohn makes an attempt to find middle ground between
these often polarized positions, and the chapter concludes by stressing the
combined roles of input and a genetic predisposition, embedding the question of
''which innate and environmental factors determine'' L1A and L2A deeply in the

Chapters 2 and 4 are structured into sections on phonology, the lexicon, syntax,
and morphology, reviewing the sequence and stages of L1A and L2A, respectively.
Chapter 2 describes both general stages (e.g. babbling, the optional infinitive
period) and acquisitional hierarchies (e.g. uncontractible copula before
contractible copula). The discussion is balanced between stressing the evidence
for innate structural predispositions and describing the role of environmental
factors and cogently, if briefly, assessing a variety of viewpoints on their
value, scope, and significance. The review is comprehensive, beginning with the
earliest environmental influences on the various components of grammar, from
newborns' sensitivity to native language prosody and the development of L1 sound
categories. Indeed, the acquisition of prosody before higher levels of structure
in L1A will be a central feature distinguishing L1A from L2A. The chapter links
the levels of grammar sequentially, from phonology to word learning, and
eventually syntax. However, the sequential and dependent nature of different
levels of structure and the interdependence between the levels of grammar, such
as how the accumulation of lexical items may lead to more detailed phonemic and
phonotactic sensitivity (e.g. Vihman 1996), are somewhat simplified.

The third chapter provides a broad and ambitious review of the evidence for
age-related declines in L1 acquisition ability, concluding that ''there are
periods of heightened sensitivity for the acquisition of first language'' (p. 99)
but stopping short of concluding that there is a single critical period.
Herschensohn instead argues for a series of thresholds whose decline is not
necessarily precipitous, and points out other areas of language (e.g. vocabulary
acquisition) in which there seems to be no apparent decline due to age. The
chapter consists of two sections, examining exceptional L1A in individuals with
atypical brains (e.g. Down Syndrome) and in those with atypical experience of
language (e.g. deaf children in certain situations). The first argues for a
dissociation between language and other cognitive abilities. The second begins
by reviewing cases of extreme isolation, acknowledging the profound limitations
of such cases for L1A in general and at the same time making measured claims
about what they do reveal. The phenomenon of international adoption is also
touched upon, in which children are frequently placed in a different linguistic
environment, often after relatively impoverished L1 experiences. Farther on,
extensive attention is given to research on deaf individuals whose first access
to language may occur at varying ages for various reasons. This population
provides the core of Herschensohn's argument for age-related sensitivities to
various aspects of language, that contribute to a more gradual decline. Ample
attention is also given to creole formation and the notion that children drive
the systematization of creoles by imposing their innate linguistic knowledge on
more variable pidgin input, although Herschensohn is also careful to point out
the controversial nature of this notion of creole genesis (Bickerton 1981,
DeGraff 1999).

The fourth chapter parallels the second in describing the process of L2A,
similarly addressing the domains of phonology, the lexicon, syntax, and
morphology. This chapter sets the stage for the ensuing discussion of age by
constructing a nuanced perspective on the comparison of L1 and L2 attainment.
Herschensohn is careful to explore the qualitative similarities in both process
and grammatical knowledge of L1 and L2, pointing out that differences in final
attainment, or even more core UG-related concepts such as parameter clustering,
do not necessarily signify a qualitative difference between L1A and L2A. The
chapter gives a comprehensive review of older models of SLA, beginning with
Contrastive Analysis and spending a fair amount of time on the Fundamental
Difference Hypothesis and the ensuing debates about the role of UG in adult L2A.
Herschensohn concludes that L1A and L2A are similar, but differ in schedule and
in the variety of other factors that come into play. This conclusion of
similarity is the pivot into the direct consideration of age in L2A.

Continuing the parallel structure of the book, the fifth chapter broadly
examines the question of a critical period for L2A. The chapter is
contextualized in a UG framework, and Herschensohn is careful to disentangle the
notions of sensitive and critical periods as well as non-biological (non-UG)
age-related factors as well. Age-related decline is not the same as a
biologically determined sensitive or critical period, and this discussion sets
the stage for the subsequent reviews of the literature on AoA, L2 learning in
exceptional populations, and end state L2 grammar in children and adults. Based
on the ubiquity of variability in L2 attainment regardless of age, the fact that
some children acquiring an L2 do not become nativelike speakers, the fact that
some adults do become nativelike speakers, and the lack of a clear inflection in
age related declines, the chapter concludes that the evidence does not support a
critical period for L2A.

Having presented detailed and convincing arguments that age-related changes in
L2 acquisition ability are not related to a biological critical period (or at
the very least that there is no conclusive evidence for such a view), Chapter 6
moves to consider what other factors might account for the effects of age.
Herschensohn first discusses research on external (environmental) and internal
(affect, motivation, aptitude, and other learner) variables. The rest of the
chapter deals with ''language and the brain'', first giving a basic overview of
brain structure and anatomical development, and then discussing a sampling of
the psycholinguistic and neuroimaging findings on language processing and
localization. The review is necessarily superficial, but supports the conclusion
that L2 processing and representation are qualitatively similar to the L1,
differing quantitatively in the timing, strength, and extent of neural responses.

The final chapter comprises a detailed summary of the entire book, beginning
with a recapitulation of the definition(s) of a biological critical period and
the biological and other reasons that might underlie other age-related
differences in language acquisition. The bulk of the chapter ties each of the
areas addressed earlier in the book to the notion of a biological critical
period for either first or second language acquisition, or both. The discussion
on language and the brain includes a useful if brief presentation of theories
concerning declarative and procedural knowledge (Ullman 2001) and gives welcome
importance to the incorporation of processing in theories of bilingualism and
L2A. This section is followed by reviews of the conclusions reached for child
L1A, child L2A, and adult L2A. While it is necessarily more superficial, readers
wishing to gain an overview of the arguments and data could obtain a basic sense
from reading this chapter before delving into the greater detail in the
preceding chapters. Of course, this also makes it a good recapitulation, and
Herschensohn carefully ties each section back to the primary question regarding
biological critical periods for language acquisition.

This book is a timely, well-researched, and useful contribution to clarifying
the issue of age effects on language acquisition. While Herschensohn is not the
first to discuss the specific nature of biological critical periods, this book
breaks ground in contextualizing maturational changes among the myriad
influences that change how individuals at different ages interact with language
in their environment during acquisition. Still more crucially, this book
provides a nuanced evaluation of the necessarily different nature of L1A and the
learning of any subsequent language at any age, and allows for an understanding
of L2A as a continually evolving process responding to biological, contextual,
and internal factors but not subject to a critical period per se. The
conclusions are a bit more complex for L1A, as Herschensohn distinguishes early
periods of heightened sensitivity to some aspects of language, particularly
morphosyntax and phonology. The concluding sections state her position perhaps
more clearly: ''Language is a human characteristic whose neural expression is
established early in childhood, yet it is open to expansion throughout the
lifetime in terms of native vocabulary or additional languages'' (p. 240), and
after L1A ''the speaker's brain is permanently altered, so acquisition of
subsequent languages could never be comparable'' (p. 234), although it clearly
builds on the foundation provided by the L1, which accounts for the obvious

The final paragraph offers a tantalizing new perspective, asking why, in the
face of critical periods for many animal communication systems, human language
does not show a biological critical period, but can rather be ''reimplement[ed]''
(p. 241). By thus turning the question on its head, Herschensohn opens the door
to seeing language acquisition as a lifelong developmental process of
interleaved changes in social environment, linguistic input, prior knowledge,
processing and learning mechanisms, and even UG. However, the book would benefit
from a greater development of this idea and its implications than is present.
For example, while knowledge of an L2 is held to be qualitatively similar to L1,
the book also sees them as fundamentally different based on the fact that L2A
occurs on the foundation of L1A. This leads to the natural conclusion, stated in
the book, that L2 speakers can never become completely native in their
knowledge, processing, or use of an L2 (although the differences may be
exquisitely subtle). Nonetheless, the bulk of the arguments rest on research
comparing L2 speakers to native speaker standards. While this is pervasive in
the literature and therefore inevitable in a review, the usefulness of the
native speaker standard bears some questioning (Birdsong 2005, Hall et al.
2006). More significantly, Herschensohn's perspective invites discussion of the
hybridity of multilinguals' competence. Again, this idea of multicompetence
(Cook 1991, 2003) is mentioned briefly, but the book stops short of considering
this as a primary way of defining the expected outcomes of L2A.

A further minor criticism is the relatively simplified presentation of
alternatives to innatism as 'associationist' approaches. There are many diverse
ways of modeling the emergence of grammar from experience (Bybee 2006), some of
which prefer not to posit any innate structure until absolutely necessary
(Langacker 2000), while others attempt to integrate nuanced models with innate
prespecifications (Jackendoff 2002), possibly leaving the boundaries of UG for
the moment undetermined. While this does not necessarily change the arguments in
the book, the portrayal of associationist approaches only in terms of
connectionist modeling obscures the detail and empirical scope of work exploring
how grammatical categories themselves may arise through domain-general learning
processes acting on input, without innate structural specifications.
Nonetheless, Herschensohn gives a prominent place to both general and
domain-specific processes in driving age effects in language acquisition.

In sum, this book presents a thorough, readable, and well-reasoned discussion of
the question of age in both L1A and L2A research. In it, Herschensohn
perceptively disentangles the complex facets of the development of the human
capacity for language from early childhood through adulthood. She makes sense of
a vast body of literature, moving beyond simple questions about the existence of
critical or sensitive periods for language to a detailed framework in which the
obvious changes in how language acquisition proceeds in different age groups can
be profitably examined.

Bickerton, D. (1981). _Roots of language_. Ann Arbor: Karoma.

Birdsong, D. (2005). Nativelikeness and non-nativelikeness in L2A research.
_International Review of Applied Linguistics_ 43: 319-328.

Bybee, J. (2006). From usage to grammar: The mind's response to repetition.
_Language_ 82(4): 711-733.

Cook, V. (1991). The poverty of the stimulus argument and multi-competence.
_Second Language Research_ 7:103-117.

Cook, V. (Ed.) (2003). _Effects of the second language on the first_. Clevedon:
Multilingual Matters.

DeGraff, M. (1999). _Language creation and language change_. Cambridge, MA: MIT

Hall, J. K., Cheng, A., & Carlson, M. T. (2006). Reconceptualizing
multicompetence as a theory of language knowledge. _Applied Linguistics_ 27(2):

Jackendoff, R. (2002). _Foundations of language: Brain, meaning, grammar,
evolution_. Oxford: Oxford University Press.

Knudsen, E. I. (2004). Sensitive periods in the development of the brain and
behavior. _Journal of Cognitive Neuroscience_ 16: 1412-1425.

Langacker, R. W. (2000). A dynamic usage-based model. In M. Barlow & S. Kemmer
(Eds.), _Usage-based models of language_. Stanford: CSLI. 1-63.

Lenneberg, E. H. (1967). _Biological foundations of language_. New York: Wiley.

Ullman, M. T. (2001). The declarative/procedural model of lexicon and grammar.
_Journal of Psycholinguistic Research_. 30: 37-69.

Vihman, M. M. (1996). _Phonological development: The origins of language in the
child_. Oxford: Blackwell.

Dr. Carlson is a postdoctoral fellow in developmental psychology at the
University of Chicago. He is interested in probabilistic grammar, the structure
of the L1 and L2 lexicon, second language acquisition across age groups, and the
role of manual gesture in bilingualism.

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