Unique errors: Those errors that cannot be categorized
as due either to interference or as developmental errors.
Interference results from the fact old habits (the first
language) must be unlearned before new habits (the
second language) can be mastered (Dulay and Burt,
1972). The important issue is whether in learning a
second language a person inevitably uses first language
and that error results from the interference of the first
language? The fact that an American learns French and
German easier than Chinese and that for Japanese the
reverse is true simply due to the way in which the
material is taught (Littlewood, 1973). Taylor (1975) has
pointed out that while learning a language humans over
generalize target language rules, reduce grammatical
redundancies, and omit those rules that they have not
learned. Flege (1999) argued on this issue and proposed
three hypotheses that account for foreign accents; 1)
Exercise hypothesis in which one’s ability to learn to
produce and to perceive speech remains intact across
the life span, but only if one continues to learn speech
uninterruptedly. 2) Unfolding hypothesis in which as
much fully developed the L1 phonetic system will be at
the starting of L2 learning the more foreign accented the
pronunciation of the L2 occurs. 3) In Interaction
hypothesis bilinguals are fully unable to separate the L1
and L2 phonetic systems, necessarily interacting with
each other. To the L2 user, however, difficulties of comprehension caused in part by phonetic and phonological
factors can certainly be as problematic in the everyday
use of the L2 as the difficulty in making oneself
understood due to non-native pronunciation.