THE
CRITICAL PERIOD HYPOTHESIS
Second
language acquisition (SLA) is affected by many different factors in its process
of acquiring a foreign language. Some of them are considered common to every
non-native speaker and they can affect in a different manner each individual.
The element that will be analysed in this paper will be the age of onset (AO),
a biological factor that is considered a strong predictor of success in SLA. According
to Granena (2013), whilst L2 morphology and syntax is often proceeded faster by
adolescents or adults through early stages, which is a rate advantage, the
expected level of ultimate L2 attainment generally diminishes with the increase
of AO. With regard to the age effects, there is less agreement between
researchers: variation in the quantity or quality of input to younger and older
learners, differences in their affective profiles or cognitive maturity are
some of these effects discussed by experts.
One
of the most known hypotheses that supporting this is the Critical Period
Hypothesis (CPH). This theory is used with two different meanings explained by Pallier
(2007). The first explanation is based on an empirical hypothesis denoting that
humans are more efficient at language learning in the first years of life (it
can also be applied to L1 acquisition). Moreover, it is an important predictor
of ultimate proficiency, because the older an individual starts to learn a
language the smaller the possibilities of reaching a native-like competence
this person will have. The second argument stands on the conviction that an
age-related decline in neural plasticity is the cause of increasing
difficulties in language learning. These two meanings must be distinguished because,
according to the first meaning, the reason for not achieving a native-like
proficiency can be due to other causes different from irreversible neural
plasticity changes, whilst the supporters of the second meaning believe that
this loss of plasticity is because of maturational factors.
However,
other researchers suggested that it could also be due to the outcome of language
acquisition itself. Penfield (1965) advocated that before the child begins to
speak, the cortex is blank and nothing is written on it. Over time, this begins
to be written and normally not erased. For the author, at the age of ten or
twelve connections produced within the cortex have now been established and
fixed in the speech of the individual. An alternative theory supported by
Pinker (1994) asserted that once the circuitry of language acquisition has been
used, it should be removed if it becomes an issue for keeping it. All neural
tissue used beyond its point of usefulness is a good starting point for being
recycled. Therefore, both theories had a
point in common: once the young learner has acquired the language or languages
around him or her, the neural modifications are impossible to reverse.
Pallier
(2007) asserts that there have been many studies carried out for the CPH. Some
of these studies were performed with animals that required depriving them from
some relevant stimulus during a period of time. On the other side, experimentation
with humans for the L1 acquisition has not been accomplished for understandable
reasons, as it would not be ethical, because it would signify the denial of
language exposure for children. Notwithstanding, some studies have been
performed with abandoned children who had little language exposure at first, and
observations suggested that their language skills were limited even after
language instruction. Other human studies performed in this area have been accomplished
with groups of deaf people who learned sign language as an L1 at different
ages. The results showed that those people who were exposed to sign language in
their first years of life had a better control of the language than those later
exposed. Eventually, those who later started (in mid-childhood) performed
better than those who were exposed first when they were ten or more.
Although
it could be asserted that critical neural changes take place during the puberty
period, it seems that it can occur much earlier. Studies conducted with deaf
children who received cochlear implants (an auditory technological device
surgically implanted to stimulate the auditory nerve in order to transmit
acoustic information to the central auditory system) displayed that there are
beneficial effect of earlier implementation in children when they are already 1
to 3 years old (McConkey Robbins, Burton Koch, Osberger, Zimmerman-Philips
& Kishon-Rabin, 2004).
Another
domain for collecting data connected to the CPH is SLA. As stated by Snow
(1978), there are two types of research designs that can be expected from this
sort of research. The first one is by comparing second language acquisition to first
language acquisition. The second one involves comparing SLA across a wide age
range. Diverse studies have shown that second language acquisition is similar
to first language acquisition, with regard to the order in which rules and
structures are acquired (Dulay & Burt, 1974), of the learning strategies
employed (Cook, 1973) and of the errors made (Taylor, 1975).
Moreover,
other studies contemplated by Ervin-Tripp (1974) and Fathman (1975) that used the
second strategy displayed that older children (even adults) proceeded faster L2
morphology and syntax. There were even other studies accomplished by Asher
& Price (1967) showed a faster listening comprehension by older
children. However, rather than showing an agreement in the obtained results,
they revealed wide discrepancies in some aspects. For instance, in
pronunciation, there were some studies that displayed a better pronunciation in
older subjects, whereas others showed a negative effect of age. There were even
other studies in which there were found cases where there were older learners
without accent in their L2, as well as cases who maintained their native accent.
Although
the studies observed so far do not endorse the predictions established by the
CPH, for Snow (1978) this hypothesis cannot still be rejected due to the
problems that will be explained. The first issue that these studies contained
was that they have only looked to a restricted age range. For example, in
Fathman’s study the ages were between 6 and 15, in the case of Ervin-Tripp the
ages were from 4 to 9, and with respect to the case of Asher and Prise, they
only took 8 adults. The second problem they presented was that age differences
were not assessed longitudinally, since all the age differences found were
given at a random point after the beginning of SLA, rather than having constant
differences in the rate of acquisition. Therefore, the only type of study that can
provide a general idea of the age differences in rate acquisition or in
ultimate achievement is a longitudinal one. In addition to this, a fairly
limited range of second language abilities were tested in most studies and the
CPH seeks to test different language abilities separately, since the
acquisition of each ability may affect differently on brain plasticity. By
doing this, contradictory findings could be explained and results would be more
accurate.
Another
sort of studies concerning the CPH in SLA have been those who have investigated
the possible effects of age at immigration. According to Stevens (2006), these
researches were made due to the high interest in the possibility of finding
critical periods in language learning.
However, the process of learning a language takes some time, thus
scholars had to take into consideration the effect of immigrants’ length of
residence in the destination country with the purpose of isolating the effects
of age at onset of L2 learning. For doing these kinds of studies, researchers
took into account three variables, “age at immigration”, “length of residence”,
and “age at testing”. Nevertheless, these three variables are linearly interconnected,
so investigators had to ignore one or two variables in their respective studies
in order to solve this problem.
The
results provided by these researches showed for instance that length of
residence in the host country hugely affected immigrants’ levels of proficiency
in their L2 (at least in the first several years after their arrival to the
receiving country). According to researchers, this was due to the fact that there
were processes related to senescence and life-cycle stages. Immigrants’ ages at
the time observations also took an important role in their investigations.
Nonetheless, as they expected before doing researches, the three variables were
impossible to consider simultaneously, and unfortunately, there are no easy
statistical techniques that can disentangle the linear dependency among them.
Chronological age was the variable that was most often omitted in the analysis,
because of its difficulty for being followed (Stevens, 2006).
To
sum up, it can be asserted that the age of onset has an important role to play
in SLA. Moreover, it has also been observed that for learning a language the
younger is usually the better. Although research will be better performed in
the future, thanks to technology improvements and the correction of previous
research errors, in this moment, it cannot be stated the exact age where
individuals will not be able to learn a language or acquire a high proficiency
language level, but instead of this, we could assert that there is a sensitive
period for learning a second language around puberty, which will not be the
same afterwards.
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