Age and Second Language Acquisition and Processing.pdf

Age and Second Language Acquisition

and Processing: A Selective Overview

David Birdsong

University of Texas at Austin

This article provides a selective overview of theoretical

issues and empirical findings relating to the question of

age and second language acquisition (L2A). Both behav-

ioral and brain-based data are discussed in the contexts

of neurocognitive aging and cognitive neurofunction in the

mature individual. Moving beyond the classical notion of

“deficient” L2 processing and acquisition, we consider the

complementary question of learner potential in postado-

lescent L2A.

The outcome of second language acquisition (L2A) among

adults is demonstrably different in many respects from the out-

come of first language acquisition (L1A) among children. Depart-

ing from this basic observation, researchers attempt to under-

stand the various sources of age-related effects in L2A.

The present article is an overview of facts and theoretical

issues concerning age and L2A. This contribution considers both

behavioral data and brain-based processing data. The review in-

cludes findings and controversies in the areas of neurocognitive

development and aging, and cognitive neurofunction in the ma-

ture brain.

A comprehensive treatment of the facts and issues is not

possible in the space available. It is hoped, nevertheless, that this

selective offering provides useful scaffolding for other articles in

Correspondence concerning this article should be addressed to David

Birdsong, Department of French and Italian, University of Texas, 1

University Station B7600, Austin, TX 78712-0224. Internet: birdsong@

ccwf.cc.utexas.edu

Age and L2 Acquisition and Processing

this volume that examine cognitive and neural aspects of L2 use

and acquisition.

Background and Terminology

Over the past 20 or so years, a great deal of empirical

research on the age question in L2A has focused on the end

state of L2A, not on rates of attainment or on stages of L2 de-

velopment. The developmental literature and comparative rate

(adult vs. child) literature are certainly not without interest, and

overviews of this research can be found in Klein (1995), Marinova-

Todd, Marshall, and Snow (2000), and Pienemann, Di Biase,

Kawaguchi, and Hakansson (2005).

However, it is essential that the end state receive its share

of attention, because it is evidence from the end state that de-

termines the upper limits of L2 attainment. Knowing the poten-

tial of the learner permits inferences about the nature of puta-

tive constraints on acquisition, including their relative strength

and ultimate impact on learning (see Long, 1990, pp. 253–259).

Accordingly, the end state is the focus of the present article. Both

as a matter of logic and as a matter of theoretic adequacy, it is im-

portant to recognize that when comparing L1A and L2A, a super-

ficial difference in ends does not necessarily imply an underlying

difference in means. Nor does similarity of ends/products nec-

essarily imply similar means/processes. Thus, for example, with

respect to the question of Universal Grammar’s (UG) mediating

role in L2A, we understand that nativelikeness at the L2A end

state does not always imply access to UG. 1 By the same token, it

is clear that nonnativelike linguistic behaviors are not necessar-

ily evidence of lack of access to UG. Researchers must be wary

of linking end-state differences in L1A and L2A exclusively to a

loss of general learning ability or exclusively to some erosion of

any putative mechanism(s) responsible for successful L1A. Thus,

linkages between product and process are to be established only

with due caution.

Birdsong

In the literature, the terms end state , final state , steady state ,

ultimate attainment , and asymptote are used more or less inter-

changeably to refer to the outcome of L2A. Note that “ultimate

attainment” has occasionally and erroneously been used as a syn-

onym for nativelike proficiency. However, the term properly refers

to the final product of L2A, whether this be nativelike attainment

or any other outcome. For divergent views of the construct of “end

state” in L2A, see Larsen-Freeman (2005) and White (2003). For

discussion of operationalizing the L2A end state, see Birdsong

(2004).

Researchers have explored several biographical variables

that might be predictive of L2A outcomes. Age of acquisition (AoA)

is understood as the age at which learners are immersed in the

L2 context, typically as immigrants. This landmark is distinct

from age of first exposure (AoE), which can occur in a formal

schooling environment, visits to the L2 country, extended contact

with relatives who are L2 speakers, and so forth. Researchers

tend to equate the terms late L2A , postadolescent L2A , and

postpubertal L2A ; these are typically operationalized as AoA of

12 years. Length of residence (LoR) refers to the amount of time

spent immersed in the L2 context. Because residence does not

guarantee exposure to and use of the L2, researchers quantify

the actual amount of contact L2 learners have with the L2 (in

spoken and written modalities) and the relative use of the L1 ver-

sus the L2 in day-to-day activities. Other experiential variables

include amount of formal training in the L2 as a foreign language

(e.g., grammar courses, corrective phonetics) as well as amount of

exposure to the L2 in so-called content courses, where nonnatives

are enrolled in high school, vocational, or university classes in the

L2 country.

Endogenous variables of interest to L2A researchers in-

clude the following: motivation (with several subtypes relating

to outcome, e.g., motivation to pass for a native, motivation to

acquire lexico-grammatical accuracy), psycho-social integration

with the L2 culture, aptitude (with several presumed components,

Age and L2 Acquisition and Processing

including imitative ability, working memory capacity, metalin-

guistic awareness, etc.), and learning styles and strategies. These

are understood to be continuous, not all-or-nothing, variables. For

overviews of these variables, see Dornyei and Skehan (2003) and

Doughty (2003).

AoA and L2 Ultimate Attainment

It is widely recognized that AoA is predictive of L2A out-

comes, in the simple sense that AoA is observed to significantly

correlate negatively with attained L2 proficiency at the end state.

This conclusion is based on the results of more than two dozen

experimental studies; see Birdsong (2005) and DeKeyser and

Larson-Hall (2005) for overviews. The areas of language most

commonly investigated are morphosyntax and pronunciation.

Typically, morphosyntax errors in production or grammaticality

judgments increase with advancing AoA, as does degree of judged

nonnative accent.

Across many studies that examine AoA and other factors

that might be related to L2 success, it has emerged that, of all

the above-mentioned experiential variables, AoA is reliably the

strongest predictor of ultimate attainment. This is not to say that

other variables, indeed some that are confounded with AoA, are

not predictive. In many cases, variables such as LoR and AoE are

controlled statistically or included as factors in the experimental

design.

The Age Function

From the actual behavioral data, a recurrent finding is that

a linear function captures the relationship between AoA and out-

come over the span of AoA (i.e., when considering aggregate data

from both early- and late-AoA subjects). In 10 surveyed studies,

the range of correlations is .45 to .77, with a median of about .64

(all absolute values). 2 The slope of the age function varies (i.e.,

it is steeper or shallower) as a function of such factors as L1-L2

Birdsong

pairing, amount of L2 use, task, education in the L2, and so on.

It is also not surprising to find, given what is known about learn-

ing and cognitive performance over the life span (Schaie, 1994;

Weinert & Perner, 1996), that there is less intersubject variation

in outcome among early arrivals than among late arrivals.

When data from early- and late-AoA subjects are disaggre-

gated, inconsistent results are obtained, producing a clouded pic-

ture of the timing and geometry of the age function. For example,

DeKeyser (2000) studied 57 Hungarian L1 English L2 subjects

with AoA ranging from 1 to 40 years, all with at least 10 years

of U.S. residence. On a grammaticality judgment test using some

items from Johnson and Newport (1989) along with some novel

items, a significant correlation of AoA with scores was obtained

( r

=−

.63, p

15, r

=−

.24,

.04, ns).

Another illustration of the disparate results of analyses of

aggregate versus disaggregated data is seen in the comparison

of the results of Johnson and Newport (1989) and Birdsong and

Molis (2001). Johnson and Newport looked at accuracy on a 276-

item grammaticality judgment by a group of Chinese and Korean

natives ( n

42, r

=−

46) with English as their L2. The Birdsong and Molis

study was a strict replication of Johnson and Newport, but in

this case, the subjects were Spanish natives ( n

61). Over all

subjects and AoAs, Johnson and Newport found a strong linear

relationship between AoA and accuracy ( r

.77, p

.01). This

.0001). However, when the subjects were divided into AoA groups

=−

.77, p

16 years, the analyses produced divergent

results. Figure 1 represents these differences.

The pattern of results seen in Johnson and Newport (1989)

is a decline in scores with increasing AoA for early arrivals ( r

≤

16 years and

.01) and an essentially random distribution of scores for

the older-arriving group ( r

.87, p

.16, ns). A quite different pattern

was obtained by Birdsong and Molis (2001). For early arrivals,

=−

.001). However, when DeKeyser broke out the data

by early- and late-arriving subjects, neither set of data yielded a

significant correlation with AoA (early arrivals n

ns; late arrivals n

=−

finding was reproduced by Birdsong and Molis ( r

−

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