什么是母语？

Stimulation in CNS development as a primary function
According to another theory, known as the Ontogenetic Hypothesis of REM sleep, this sleep stage (also known as active sleep in neonates) is particularly important to the developing brain, possibly because it provides the neural stimulation that newborns need to form mature neural connections and for proper nervous system development.[14] Studies investigating the effects of active sleep deprivation have shown that deprivation early in life can result in behavioral problems, permanent sleep disruption, decreased brain mass,[15] and result in an abnormal amount of neuronal cell death.[16] Further supporting this theory is the fact that the amount of REM sleep in humans decreases with age, as well as data from other species (see below).
One important theoretical consequence of the Ontogenetic Hypothesis is that REM sleep may have no essentially vital function in the mature brain, i.e., once the development of CNS has completed. However, because processes of neuronal plasticity do not cease altogether in the brain,[17] REM sleep may continue to be implicated in neurogenesis in adults as a source of sustained spontaneous stimulation.

‪Critical period hypothesis‬

The critical period hypothesis is the subject of a long-standing debate in linguistics and language acquisition over the extent to which the ability to acquire language is biologically linked to age. The hypothesis claims that there is an ideal 'window' of time to acquire language in a linguistically rich environment, after which further language acquisition becomes much more difficult and effortful.
The critical period hypothesis states that the first few years of life is the crucial time in which an individual can acquire a first language if presented with adequate stimuli. If language input doesn't occur until after this time, the individual will never achieve a full command of language—especially grammatical systems.
The evidence for such a period is limited, and support stems largely from theoretical arguments and analogies to other critical periods in biology such as visual development, but nonetheless is widely accepted. The nature of this phenomenon, however, has been one of the most fiercely debated issues in psycholinguistics and cognitive science in general for decades. Some writers have suggested a "sensitive" or "optimal" period rather than a critical one; others dispute the causes (physical maturation, cognitive factors). The duration of the period also varies greatly in different accounts. In second language acquisition, the strongest evidence for the critical period hypothesis is in the study of accent, where most older learners do not reach a native-like level. However, under certain conditions, native-like accent has been observed, suggesting that accent is affected by multiple factors, such as identity and motivation, rather than a critical period biological constraint (Moyer, 1999; Bongaerts et al., 1995; Young-Scholten, 2002).

ysun wrote:

实际上，此讨论发起者的初衷是想指出这一点： “Bogus claims about native language status actually constitute deception”。依我看，这个问题只能靠自觉，用不着去 verify，也难以实施这种 verification。

Should “native language” claims be verified?
http://www.proz.com/forum/prozcom_suggestions/227485-should_“native_language”_claims_be_verified.html

wherestip wrote:

I agree. Someone's native language status is not something that's easily verifiable.

IMO, for all practical purposes, an English-speaking agency should be able to tell if the English quality of an end product is good enough for what they want to do with it.

ysun wrote:

这样以来，今后还有哪个 native speaker of Chinese 敢去参加讨论？

ysun wrote:
再说，native speakers 未必就都是水平很高的翻译。