The phonological processes that occur in speech may be thought of as consisting of two main types:
- structural simplifications
- systemic simplifications
Unlike structural simplifications, systemic simplifications do not alter the syllable structure of a word. Rather, they systematically vary a particular type of speech sound and replace it with another speech sound. Systemic simplifying processes may involve substitutions of one speech sound by another, and assimilations where one speech segment is transformed into another owing to the influence of a neighboring segment.
There are many different types of systemic simplification observed in typically developing speech. Some of the more common ones are listed below and they are summarized in Figure 1.
- vowel harmony
- consonant harmony
- voicing change
- feature synthesis
Figure 1. Summary definitions of systemic phonological processes