At the time there had been enough discovery of a number of feral children to support this hypothesis. However, other variables were problematic, as these same children had been neglected, deprived and usually abused. Many were half starved and most had suffered isolation. With all these factors involved it was difficult to limit the variables in order to establish cause and effect.
Later, other linguists tried to tie this theory also to second language acquisition with varying contradictory results. Finally, neurobiologists did manage to identify a portion of the brain that seems not to develop if a “second” language is not acquired by a certain pivotal age, generally coinciding with puberty. However, just what exactly is meant by a second language is not cast in stone. Does Latin qualify? What about children’s code language for play? Do other jargon sets qualify, such as mathematics terminology, psychology vocabulary or academic English? What about a second dialect sufficiently different from the mainstream language? Little or no research has been done with these languages as the “second language” acquired, so it is still unanswerable. However, it is this researcher’s suggestion that perhaps any sufficiently large complex symbolic system will fill this void. However, in the case of a dialect, if the first language is a dialect of the mainstream language, is there a critical period beyond which it becomes problematic for the learning of the mainstream language?
Lenneberg first hypothesized the existence of a critical period for language learning in 1967, and it was supported by the case study of Genie, who had little or no exposure to language until age sixteen. He hypothesized that “language acquisition is impossible before two due to maturational factors, and after puberty because of the loss of ‘cerebral plasticity’ caused by the completion of the development of cerebral dominance, or lateralized specialization of