Once the word-picture relationship is mastered and the child's vocabulary is large enough to require making phonetic discriminations again, says Stager, the brain is able to make all the phonetic distinctions it needs.
At the level of morphology, they may find it difficult to produce correct forms of verbs, nouns, adjectives, articles, and so forth, especially when the morphological distinction hinges on subtle phonetic distinctions, such as the presence of a plosive or fricative sound in consonant clusters or the distinction between two similar vowels (lead versus led).
There is also evidence that visual cues can enable non-native speakers to make phonetic distinctions that they are not sensitive to when only auditory cues are available (Navarra & Soto-Faroco, 2007).
Functionally there is evidence that children with language impairment have limitations in phonological short-term memory and also difficulties in processing rapidly changing sounds, called auditory processing, which is critical for phonetic distinctions in speech (Bishop et al. 1999, 2006; Tallal et al. 1996).
It is also important to bear the phonetic-phonemic distinction in mind in discussing the reconstruction of a protolanguage.
At the segmental level, the deviations may be limited to phonetic properties without really compromising phonemic distinctions, or they may blur phonemic distinctions and thus have more serious consequences for intelligibility.
It could also help make speech-processing systems more portable, since information about lower-level phonetic units could help iron out distinctions between different speakers' pronunciations.
Characters reflect shape distinction needed to perceive different phonetic information of words.
More problematic deviations may arise when the difficulty in perceiving and realizing phonetic features of the target language that are not distinctive in the mother tongue leads non-native speakers to blur the distinction between phonemes in the target language, thus producing one phoneme instead of two distinct ones.
It is flexible and can therefore be either phonological or phonetic (Oppenheim and Dell, 2010; see Vigliocco and Hartsuiker, 2002 for a related distinction).
