A simple example of co-articulation is the articulation of [k] in key and coo. When uttering key, while the back of the tongue is making closure with the top of the mouth for the [k], the lips not ordinarily involved in articulating [k] begin to spread in anticipation of the following vowel [i]. Similarly, when uttering coo, the lips round during the articulation of [k], in anticipation of the upcoming [u]. One aspect of co-articulation, the, is that the actual articulation of a phonological segment can be influenced by upcoming sounds. This is sometimes referred to as regressive assimilation. Co-articulation can also be influenced by a phonological segment that has just been produced, a phenomenon sometimes called progressive assimilation.
What is most important for the present discussion, however, is that sounds produced by speakers are not discrete or separate units, but rather form part of a continuous speech signal. The mental representation of the phonological form of an utterance is definitely segmental, phonemes lined up one after the other; however, in the process of speaking, phonemes overlap and blur together.
One final aspect of co-articulation is central to understanding the production and perception of stop consonants. Stops involve producing a complete closure somewhere in the vocal tract: [p] and [b] involve closure at the lips, [t] and [d] closure at the alveolar ridge, and [k] and [?] closure at the velum.
In sum, this process of co-articulation is essential in the production stage, it is clear that we cannot convey a meaning with pronunciation of isolated words, it is necessary that we co-articulate the words in order to be understood.
Mind Explorer/ October, 2013 15