Since the 1960s much research has been also done on the age factor in foreign language learning. Nevertheless the results were contrary to the common misbelieve and supported the generalization that adults in a formal learning setting learn faster than children. It does not appear applicable to the pronunciation, however. Despite the fast progression in grammar, adult learners rarely achieve a native-like accent. Selinker (1972) goes further and asserts that once language learners have passed the critical period, their pronunciation becomes inevitably fossilized. This belief is supported by an extreme but widely accepted Kissenger effect sample. It is known that although Henry Kissenger, German-born American political scientist and diplomat, had magnificent and fluent control on the English language, he had a German accent while speaking English.
Assertions such as Selinker’s and extreme samples like Kissenger effect has set ground for many researchers’ ideas as it is too difficult or impossible to change pronunciation once a certain age of pronunciation has been reached. However they are not able to put on view the impossibility of defosilization. That is, although it is very hard to change learners’ pronunciation after the critical or sensitive period, it does not mean that there is no rehabilitation for this deficiency. For example Acton (1984) states that pronunciation deficiencies frequently seem to be rigid or inflexible. Nevertheless, he suggests teachers some patience and learners a concerted effort. Since, the learner, learners’ FL learning setting and the source of the pronunciation problem need to be analysed in depth to desuggest this kind of inhibitions. In brief, learners should not only be prepared to rehabilitation but also encouraged to make a concerted effort.