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GRS LX 700
Language Acquisition
and
Linguistic Theory
Week 8b.
The Critical Period Hypothesis
L1A vs L2A

Some properties of L1A:




Fast
Seemingly effortless
Uniformly successful in reaching target.
Some properties of L2A:



Slow
Hard
Typically does not end in native-like ability.
L1A vs L2A



Few, possibly no, adults reach the level of tacit
or unconscious knowledge of the grammar of
the L2 that puts them on a par with native
speakers.
L2A often hits a brick wall after a certain point
(“fossilization”), stuck with errors in variation with
correct forms.
L2A isn’t “equipotent”—the particular L1 and L2
pairing has an effect on the overall difficulty and
problem areas.
C. L1A: fast, easy, successful.
A. L2A: slow, hard, failure-prone.

Suggests that kids are “built to learn
language” in a way that adults are not.

Perhaps there is a “sensitive period” early
in life where one absorbs languages? A
sensitive period which ends at some
point…
Lenneberg 1967

Lenneberg 1967 (or Penfield and Roberts
1959) is usually considered to be the
written origin of this idea that there is a
“critical period” or “sensitive period” for
language acquisition.

He based this on several observations,
including the observation that critical
periods are biologically common.
What makes us think there
might be a critical period?

Concerning L1A, there are (traumatic)
cases of delayed language exposure
which together seem to show that only if
recovered before age 10 would normal L1
language development occur. This
includes Genie (started at 13;7, learned
some but stopped short of native-like
attainment in morphology and syntax)
What makes us think there
might be a critical period?

Another case of severely delayed language
access (but without abuse) is Chelsea,
misdiagnosed as retarded in early childhood,
when in fact she was congenitally deaf—only
discovered when Chelsea was 31.

Chelsea’s utterances have almost no
discernable structure at all; her speech was less
language-like than Genie’s.
How early is early enough?

Isabelle (imprisoned with her mute, uneducated
mother), starting at 6, rapidly caught up to
normal age-levels.

Jim, hearing child of deaf parents, brought into
speech contact around 3;6, rapidly caught up in
spoken language, reaching age-norms by 6.
How early is early enough?

Newport & Supalla’s study of ASL as L1 among
congenitally deaf individuals, who started
learning ASL at different ages.



Exposure before 6 yields native competence, uniform
error types (4-6 did slightly less well).
Exposure after 7 yielded more errors in closed-class
items, later correlated with evidence of more
“holistically” (rote?) learned elements.
Exposure after 12 much higher error rate and variable
error types, more frozen forms.
Seems clear enough



There is some kind of advantage to L1A
within the “sensitive period”.
Is it language specific? Or is there
something about overall cognitive
development that can explain this?
Once you get L1 within the sensitive
period, is that good enough (does that
“get it started”) for L2A even after the
sensitive period?
To reiterate…

Is there a critical period for L1A?


Evidence just reviewed suggests probably.
Does this critical period affect L2A?
Is it easier to learn an L2 inside the critical period?
 It is possible to learn an L2 outside the critical
period?
 Does it just depend on having learned an L1 inside
the critical period? (Kind of hard to distinguish from
there being no critical period for L2A)

About critical periods

Just a note: It’s pretty uncontroversial that there
is some decline in the ability to learn language
that happens with age. Nobody disputes the fact
that it’s harder to learn a second language later
in life.

The question is: Is this caused by an irreversible
neurological change? (A critical period) Is it
impossible to “learn an L2” after the end of the
critical period? Or does it just get harder to learn
stuff as you get older? Why does it seem to be
particularly acute with language learning?
About knowledge

We can distinguish between two types of
knowledge:
language competence (acquired competence)
 learned linguistic knowledge


The first is generally unavailable to conscious
reflection. The second is quite often conscious.

An L1 example of LLK is Don’t end your
sentences with a preposition, which if followed
threaten to result in travesties like: This is the sort
of arrant pedantry up with which I will not put!
About knowledge

The critical period hypothesis is about obtaining
acquired competence (not learned linguistic
knowledge) and it makes a claim about whether an
L2 speaker can obtain a native-like competence of
an L2.

People can always gain LLK in an L2 as well, learn
rules, apply them, maybe get so practiced at it that
it becomes second nature, but this still wouldn’t
rise to the level of acquired competence.
L2A and age of initial
exposure




Adults proceed through early stages of
morphological and syntactic development faster
than children (time and exposure constant).
Older children acquire faster than younger children
(morphology and syntax; time and exposure
constant)
Child starters outperform adult starters in the end.
So, age improves rate, at least initially, but
negatively affects ultimate level of attainment.
Phonology—6

Other studies of phonological acquisition
suggest that 6 years old is a critical one for
attainment of native-like phonology. The period
between 6-11 generally still results in some
detectible accent.

Generally tested by having native speaker
judges listening (to accent, presumably) and
guessing which were native speakers and which
weren’t.
Morphology, syntax,
semantics—15

A few studies show that L2 speakers with
an initial exposure prior to 15 did
significantly better than L2 speakers with
an initial exposure after 15 in the domain
of syntax and morphology.
Comprehension—10

A small set of results (Oyama 1978,
Scovel 1981) suggest that ability to
comprehend “masked” speech and
recognize foreign accents has a
discontinuity at around age 10.
Several “critical periods”

So it seems that there is an age-sensitivity,
but it is not even language specific, it is
subpart-of-language specific.
Phonology—6
 Morphology, syntax, semantics—15
 Comprehension—10
 …?

Why isn’t it strange that there
should be (a) critical
period(s)?
 There are critical periods attested all over the


biological world.
The visual system is a favorite example. In
experiments done on macaque monkeys, it was
determined that there is a critical period for
development of binocular vision cells in the
visual cortex (tested by monocular deprivation)
Recovery after CNS damage: disappointingly
limited in the adult brain, but can be nearly
100% in the immature nervous system.
Why isn’t it strange that there
should be (a) critical
period(s)?



Vision studies replicated in cats (Hubel & Wiesel 1962,
1970).
In fact, vision studies “replicated” in humans as well; there
seems to be a visual critical period at around age 6, after
which providing previously delayed visual stimuli is of no
use. (Congenital opacities of the cornea; surgery performed
on juveniles or adults does not restore sight)
Imprinting in birds; just after birth, they “become attached” to
a prominent moving object in their environment (typically,
the mother). This attachment persists. But it can only be
done sometimes in the first few hours, for some species.
(For a demonstration, see the movie Fly Away Home)
Why isn’t it strange that there
should be (a) critical
period(s)?
…The development of form perception and the binocular
vision necessary for depth perception proceed in stages
after birth. Each stage culminates in one or more
developmental decisions, many of which are irreversible. In
each stage, appropriate sensory experiences are
necessary to validate, shape, and update normal
developmental processes. Consequently, the effects of
sensory deprivation are most severe during a restricted and
well-defined period early in postnatal life when these
developmental decisions are still being made. (Kandel,
Schwartz, Jessell 3d ed. 1991, p. 956)
Why isn’t it strange that there
should be (a) critical
period(s)?
…Critical periods of development generally do not have sharp
time boundaries. Different layers within one region of the
brain may have different critical periods of development, so
that even after the critical period for one layer has passed,
rearrangement of the layer may still be possible because
the entire region has not yet fully developed. For example,
8 weeks after birth layer 4c in the visual cortex of the
monkey is no longer affected by monocular deprivation,
whereas the upper and lower layers continue to be
susceptible for almost the entire first year.. (Kandel,
Schwartz, Jessell 3d ed. 1991, p. 957)
What might cause
a critical period?

Social / cognitive factors that covary with age?
(an “intervening variable”); e.g., attitude,
motivation, empathy, self-esteem, …



Doesn’t seem to get at the uniformity across
situations. Why phonology at 6, morphology at 15?
Difference in the input? Unlikely to cause this big
of an effect, and also unlikely to be as consistent
as the facts require.
Cognitive development provides other learning
mechanisms which overwhelm our LAD
mechanisms? Is this detectibly different? Is it
even conceptually different?
Brain development?



Brain = mass of interconnected neurons.
Certain areas of the brain have specific
functions (visual cortex; auditory cortex;
motor cortex) despite high levels of
interconnectivity.
Is the critical period due to loss of brain
plasticity in the language area?

Does language specifically have its own
area?
Localization


Early evidence for localization came from aphasic
patients—patients with specific linguistic deficits
due to brain lesions, which could be correlated
with location in an autopsy.
Broca, French surgeon, 1861.




Saw patient who lost had his ability to speak (could only
utter the monosyllable tan except if agitated—reputedly
often—when he could swear).
Intelligence, comprehension spared
Gradual paralysis of right side of the body.
In autopsy, a lesion was discovered in what became
known as “Broca’s area”—left hemisphere, frontal lobe.
Broca’s area
Spinning brain
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.

This came from here:
http://brainmuseum.org/Specimens/primates/human/qtvrbrains.htm
Lateralization

Broca’s area is on the left hemisphere, not
symmetrical. (Some very small variation
with handedness—right-handed, almost
exceptionless; left-handed, some
variation).

By now various regions of the brain have
been correlated with certain kinds of
aphasia
Lateralization



The two hemispheres of the brain also seem to
have somewhat different functions.
Left hemisphere generally controls the majority
of language function.
Right hemisphere appears to be involved in
maintaining focus of attention, and also possibly
prosody.

Right hemisphere lesions have been known to
severely affect ability to analyze metaphors,
summarize complex texts, as well as disrupt prosody
in otherwise normal language
Child aphasia

Acquired aphasia during childhood is almost never fluent
(mutism), but they recover rapidly (lasting effects
generally only slight word-finding and vocabulary
difficulties).

Recovery is faster, better than in adult acquired aphasia,
but not complete.

Early enough, right hemisphere can take over language
functions after a serious loss in the left hemisphere, but it
doesn’t do as good a job.
Child aphasia

Lenneberg’s summary of the results of left
hemisphere lesions as a function of age:





0-3 months: no effect
21-36 months: all language accomplishments disappear;
language is re-acquired with repetition of all stages.
3-10 years: aphasic symptoms, tendency for full recovery
11th year on: aphasic symptoms persist.
Basis for his view that lateralization was tied to critical
period.
What might cause
a critical period?

Associated with lateralization of language
processes in the process of brain
development?

Interesting, but the timing is probably off.
Lateralization seems to be complete by
around age 5, long before the syntax
critical period. Maybe implicated in some
way in the phonology critical period?
What might cause
a critical period?

Brain development. Myelinization of axons
precludes further connections (limits
plasticity). Myelinization happens more
slowly—in fact, it might miss the critical
period on the other end, still going on after
15. Plus, we’d still like to know why the
particular sequence we see, even if
myelinization is the answer.
Myelinization & neurons
What might cause
a critical period?

Bottom line: We don’t really know.

Neural development seems like a
promising place to look, but there are very
few things actually known about the
connection between language and
neurons, or even about neural
development (beyond description).
Johnson and Newport (1991)

Aiming to test the critical period
hypothesis by looking at correlations
between eventual performance and age of
initial exposure to the target language.

In particular, they were trying to focus on
whether purportedly universal properties
of language exhibited in L2 show an age
effect.
Subjacency

Johnson & Newport used grammaticality
judgments to try to get at the language
learners’ interlanguage competence,
testing subtle contrasts that native
speakers make.

Their primary test looked at Subjacency
violations (characterizing the possible whquestions in a language).
Subjacency review

Certain kinds of phrases that cannot contain the
trace of a wh-movement. If you try to relate a whword at the beginning of the sentence to a trace
inside one of these islands, the result is
ungrammatical (or bad-sounding) sentence.




*What did you ask whether John will buy — tomorrow?
*Who did you see the book John gave — on the table?
*What did you laugh after John brought — home?
*What did John eat — and a muffin?
Language variation


Wh-in-situ languages tend also to allow a
wh-question with the wh-word inside of an
island to be asked (unlike in wh-movement
languages).
So, in Japanese, it is perfectly possible to
ask (in Japanese):
I saw [the book John gave who] on the table?
 I laughed [after John brought what home]?

Subject-Auxiliary Inversion

Johnson & Newport look at second language
learners’ control of Subjacency in comparison to
second language learners’ control of SubjectAuxiliary Inversion (TC movement).

SAI is considered by them to be an “Englishspecific” rule (not a universal constraint like
Subjacency, allowed by UG but in a sense not
required by UG).
Subject-Auxiliary Inversion


So, what Johnson & Newport were
assuming was essentially something like:
When learning a language:
(If the language has (wh-)movement), LAD is
required to pick out the Subjacency rule and
add it to the grammar of the language being
built.
 A language may or may not opt to formulate a
rule like SAI and add it to the language being
built (language-particular, not provided by UG,

Johnson & Newport (1991)

J&N wanted to compare the ability of native speakers of
Chinese (a wh-in-situ language) to learn/use Subjacency
(a universal principle, provided by UG) and subjectauxiliary inversion (an English-specific rule, supposed to
be part of English over and above UG).

The idea is that if universal principles are provided by UG
and there is a critical period, young learners (within the
critical period) might have “access” to it whereas older
learners might not (given that the L1 did not make use of
Subjacency).
J&N91: Study 1

Tested:






declarative controls
subjacency violations
wh-questions satisfying subjacency
SAI error (“English-specific”)
simple wh-question controls (filter)
Subjacency violations covered a number of
possible settings for bounding nodes.
J&N91: Study 1 results

Adult learners (ChineseEnglish) did much worse
(accepted ungrammatical sentences) than native speakers.

L2’ers did better on SAI than on subjacency; subjacency
doesn’t seem “privileged”.

Response bias was ruled out; there is a slightly better than
chance influence of subjacency in L2’ers.

L2’ers seem to accept sentences that exemplify violations
of subjacency with bounding nodes that hold in all
languages.

They verified that subjacency violations were by asking for
answers—so we could tell where wh-words moved from.
J&N91: Study 1

So, the adult learners didn’t do well at all
on Subjacency tests—and not even better
on Subjacency than SAI. And the actual
responses didn’t seem to follow from a
missetting of the bounding node
parameters either.
J&N91 (Study 2)

Johnson & Newport looked at how second
language learners fared with respect to
Subjacency (“UG”) and Subject-Aux
Inversion (“English-specific”), and what
effect “initial age of immersion” had. They
were looking for evidence of a critical
period for language learning (in the form of
“learning” the syntactic principle of
Subjacency).
J&N91 (Study 2)

What’s the effect of initial age of
immersion?

21 speakers ChineseEnglish with initial
ages between 4-16.

21 more with initial ages between 17-25.
J&N91 (Study 2)
36
34
32
30
28
Subjacency
No-inversion
26
24
22
20
18
Native
4 to 7
8 to 13
14 to 16
adult
J&N91 (Study 2)

They conclude: Their results are incompatible
with the view that nothing’s different between
late and early L2 acquisition.

There seems to be a more rapid drop-off of
ability to use the putative universally available
principle of Subjacency in one’s L2 if initial
immersion is after 14 years old.
But what question are we
answering?

White (2003, ch. 8) points out that J&N91 are
really asking a different question:



Does age-of-exposure/immersion affect a L2’ers
achievement of the grammar of L2 that a native
speaker would have?
Answer seems to be yes.
But does that mean the ultimate grammar (for
late learners) is UG-unconstrained?

Of course not, at least to the extent that there are
languages for which native speakers could behave
like J&N’s L2’ers.
A possible interpretation

Chinese allows topicalization, not derived by
movement:


zheben shu [[du guo pro de] ren] bu duo
this book [[read ASP pro C] man] not many
‘This book, the people who read (it) aren’t many.’
If a fronted wh-phrase is reanalyzed as a kind of
topic with a null resumptive, a language that
looks like English without Subjacency would be
the result. And it would still be UG-compliant.

(Hawkins & Chan 1997)
Those who disagree…



Despite all of this, there are still those who
maintain that there isn’t a critical period.
The primary evidence brought in favor of this is
that we can find isolated, rare instances of
people who have learned a second language in
their adult years (after a critical period should be
over) who pass for native speakers on various
kinds of tests.
What are we to make of this kind of evidence?
White & Genesee (1996)


W&G are among the non-believers in a
critical period. They don’t believe the
results of previous studies are really
representative of what level of
competence is achievable.
Instead, let’s find people who are likely
candidates (near-natives) and test them
(and compare their initial ages of
immersion)
White & Genesee (1996)

Their subjects seem to distribute as you’d expect,
though—the young learners are the near-natives, the
old learners are the non-natives.
Age groups
Group
0-7
8-11
12-15
16+
Totals
Near-native
22
7
7
9
45
Non-native
6
5
11
22
44
White & Genesee (1996)

Their tests were grammaticality judgments and question
formation tasks testing subjacency and also measuring
reaction time.

Their results from the GJ task showed that their
categorizations of the subjects were right—the nearnatives performed like native speaker controls, and often
significantly different from the non-native speakers. The
QF task showed the same thing.
White & Genesee (1996)

W&G’s conclusion: It is possible for ultimate
attainment to be native-like (to the point where
you can’t experimentally tell a near-native from a
native speaker). And there seems to be no
particular effect among the near-natives of initial
age of immersion.

The age effect must be due to something else
other than a “loss of UG”.
White & Genesee (1996)

Of course, English and French are a lot
alike—is this an artifact of that? Did these
L2’ers do so well because they could carry
their parameter set over from French
almost wholesale? Alluding to another
study (White & Juffs 1996), W&G suggest
no—Chinese not-quite-near-natives
caught about the same number of
ungrammatical sentences as native
English speakers.
So where are we?






There is lots of evidence from neuroscience that some
aspects of brain development are subject to critical
periods.
The evidence seems to show that people who start
learning a second language relatively late are much less
likely to approximate native speaker competence.
The evidence may not quite manage to show that late
learners cannot reach near-native levels.
So is this inconsistent with a biological explanation?
Are the “near-natives” just really good with LLK?
Or, is it simply that the near-natives had to make use of
something other than a (full-strength) LAD to get there?
DeKeyser (2000)

Adopts the familiar hypothesis that early
language learning is due to unconscious,
automatic, “implicit” acquisition and late
language learning relies on more conscious
“explicit” learning.

Note: there is a similar distinction one can make
between explicit and implicit knowledge
(automatization, cf. driving a standard transmission
car). These are two different things. One could
imagine explicit learning procedures might still lead to
implicit knowledge (cf. driving a standard transmission
car).
DeKeyser (2000)

Basic prediction of the CPH: Late learners
no longer have the implicit learning
mechanism that early learners had. They
must rely on analytic explicit learning
procedures to learn language.

There are individual differences between
people in their analytic and verbal abilities.
DeKeyser (2000)


Therefore:

All late-learning achievers of near-native status must
have high verbal ability.

Early-learning achievers of (near-)native status will
not show any effect of verbal ability.
Ran a Johnson & Newport-like study to see if
these correlations hold.
DeKeyser (2000)

Tested 57 native speakers of Hungarian, all in
the US for at least 10 years.



Non-Indo-European, quite different from English in
many respects.
Almost no exposure to English prior to moving to an
English-speaking country.
Used modified version of Johnson & Newport’s
grammaticality judgment task, then tested on a
Hungarian verbal aptitude test.
DeKeyser (2000)

Aptitude test:




Aptitude scores did not correlate with




Average 4.7 of 20, std. dev. 2.79.
6 or above (+.46) was considered “high aptitude”.
Resulted in 15 individuals.
Age of arrival
GJ test score (whole group)
GJ test score (early learners only < 16)
But did correlate significantly with

GJ test score (late learners only ≥ 16)
DeKeyser (2000)


Several types of items on the GJ task.
High correlation with age of arrival on:








Tom working in his office right now.
Tom is reading book in the bathtub.
The beauty is something that lasts forever.
I need to get some informations about the train
schedule.
What Martha is bringing to the party?
Who you meet at the park every day?
I want you will go to the store now.
The student eats quickly his meals.
DeKeyser (2000)

Low correlation with age of arrival on:
The dinner the man burned.
 The woman the policeman asked a question.
 The students to the movies went.
 Bites the dog.
 Knows John the answer to that question?
 The girl cut himself on a piece of glass.

DeKeyser (2000)


So, different things seem to be differently
affected by the age effects, but there are
significant age-of-arrival effects on many of the
items.
Looking now at the few late learners who did
achieve a high test score, we find that they all*
had high verbal aptitude scores too.
 *One
didn’t, but DeKeyser argued that his score
wasn’t representative of his analytical ability.
DeKeyser (2000)




Early learners got high test scores regardless of
their aptitude scores; the only late learners to get
high test scores had high aptitude scores.
Years of schooling did not correlate with GJ
scores.
Exactly as predicted if post-CPH learners have
to rely on more explicit learning mechanisms to
learn a second language.
But note! that this doesn’t mean that there isn’t
some kind of implicit learning happening, only
that it seems to be facilitated by explicit learning.
DeKeyser (2000)


Some structures, still, showed no correlation
with aptitude—everybody got them, regardless
of age-of-arrival, regardless of aptitude.
Why? DeKeyser suggests it is a function of
salience.


SAI and do-support in yes-no questions (initial),
pronoun gender (corrected), basic word order (initial,
final).
Concludes: CPH exists and constrains implicit
learning mechanisms.
So where are we?

The onset of language takes place at early
infancy, if not already at birth.

At least by 6 months, infants are able to
discriminate linguistic sounds (phonetic
inventories, open syllables) from one another
and from non-linguistic sounds.
So where are we?

There is an initial sensitive period for phonetic
perception that is already over at 10-12 months
of age but that appears to be overcomeable at
least to some extent.

Prior to this, children can discriminate linguistic
sounds not only from the language they are learning
as a native language, but also from other languages
as well. After this, their ability wanes, although it
seems to still be possible even for adult learners to
regain the ability to distinguish non-native sounds with
training or with the right experimental conditions.
So where are we?

Delayed first language acquisition is incomplete
when the onset of language is after age 4; the
later the age of onset, the less complete
acquisition is likely to be.
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“Complete” = “as measured against the normally
developing linguistic community”
Newport (1990) studied congenitally deaf adults with
different initial ages of exposure to ASL and found
that even those whose initial age of exposure was as
early as four were outperformed by those whose
initial age of exposure was prior.
So where are we?

Late first language acquisition is less
successful in the long run than equally late
second language acquisition.

Many studies combined show this sort of
effect; it appears to be vital to learn a native
language early, whereas the “window” doesn’t
seem to completely close on highlysuccessful second language acquisition until
quite a bit later.
So where are we?

More mature learners generally make faster
initial progress in acquiring morphosyntactic and
lexical aspects of second language.

The general idea here is that more mature learners
have more advanced general cognitive processes
and problem-solving ability that allows them to better
deal with the task of learning the morphology and
syntax as a problem to be solved. Perhaps this is
indicative of a role for LLK? In the long run, though,
more mature learners are generally less successful.
So where are we?

An increasing age of onset for second language
acquisition is correlated with declining ultimate
attainment in pronunciation and morphosyntax across
age groups, this pattern beginning typically with an onset
age of 6 to 7 in childhood and continuing into adulthood.
In adult learners, the association between onset age and
declining outcomes is most strongly manifested in the
oral aspects of second language proficiency.
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Learning a second language without an accent is very difficult
after quite an early age.
So where are we?

Second language studies have not provided any real
support for a critical period terminus at puberty, just
somewhere. Some adult learners are capable of nearnative, if not native-like, performance in a second language,
whereas some children are less successful than others.
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Puberty is another biologically scheduled process that is tempting to
compare with a “critical period” for language acquisition. However,
puberty is not itself contemporaneous with any observable linguistic
milestone—it appears to be also maturational, but not directly linked
to linguistic capacities.
Whatever critical period there is, it seems to be somewhat
“overcomable” either with effort or perhaps in terms of individual
differences…?
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