The issue of CP for SL acquisition is considerably less clear and remains among the most
hotly debated issues in SL research. It should be noted that a CP for SL acquisition does
not necessarily follow from a CP for FL acquisition. The latter means that there is a limited
period in the early years of life when individuals can exercise a (special) language learning
ability, and if this ability is not exercised (e.g. as a consequence of linguistic isolation
during this period), it dies away and can never again be exercised. In the case of SL
acquisition, we have individuals who have successfully exercised their language ability
during the CP and have attained the normal high level of competence in their FL. The
crucial question here is: does the language ability inevitably die away after the CP
irrespective of whether it has been exercised during the CP or not? In the absence of
compelling evidence to the contrary, we cannot discount the possibility that, once the
language ability has been exercised, it stays alive.1
For many, the fact that, in contrast to
late FL starters, adult SL learners can achieve a very high level of competence in the SL
can be seen as evidence favoring such a position. Others have pointed to the highly
variable success rate in SL learning and the widely known fact that native competence in
the SL can only be achieved by very young starters, suggesting that maturational
constraints apply to SL learning as well.2
There have been a number of studies (e.g. Oyama
1976; Patkowski 1980, 1994; Johnson & Newport 1989, Thompson 1991, among others)
showing a distinct advantage of young children over adult SL learners with regard to
ultimate attainment. While such studies have often been the target of severe criticism for
being methodologically flawed, no one actually seems to dispute the generalization that on
average children achieve higher levels of SL proficiency than adult learners. According to
critics of the CP hypothesis, however, this alone cannot be taken as conclusive evidence
for the existence of maturational constraints on SL acquisition. Bialystok (1997: 117)
argues that this is a descriptive generalization which may be statistically correct, but from
which "nothing inevitable follows". The crucial question then seems to be not so much
whether children are more successful SL learners than adults, but rather whether it is
impossible for adult SL learners to achieve native competence in the TL, because, as Long
(1990: 274) puts it, "[t]he easiest way to falsify [the CP hypothesis] would be to produce
learners who have demonstrably attained native-like proficiency despite having begun
exposure well after the closure of the hypothesized sensitive periods". There have been
several experimental studies in recent years (Birdsong 1992, Ioup et al. 1994, Bongaerts et
al. 1995, White & Genesee 1996) in which the researchers identified–usually after rigorous
screening - some highly proficient SL learners whose exposure to the SL had only begun in
adulthood, and using various experimental techniques (more often than not, grammaticality
judgements) compared their competence in the SL to that of native speakers. The results
from these studies appear to indicate that achieving native competence by adult SL
learners, while extremely rare, is not impossible, thus arguably proving that the CP
hypothesis does not hold for non-primary languages. Other serious arguments against CP
for adult SL acquisition have been raised as well. Bialystok and Hakuta (1994) re-analyse
the data presented in Johnson & Newport (1989) and argue that there is no evidence for an