Once speakers have decided what words to use, they will have to retrieve the corresponding phonological forms from their lexicons, build phonological representations of utterances, and pass this information on to the phonetic implementation module. Phonological processing The information available to hearers in the acoustic speech signal is very large indeed. A considerable research effort has been devoted to the question of how listeners decide where words begin, that is, when it is useful to entertain the hypothesis that a certain part of the speech stream constitutes the beginning of a word. Likewise, the extent to which speakers may provide strings of perceived segments with syllable structure may depend on the role which syllable structure plays in the phonology of the language.
Phonological theory aims to account for the shapes of the sound systems of the world's languages.
A prerequisite to serving this aim is the availability of reliable data. Although it may go too far to say that every new language provides at least one aspect which overturns our unspoken conceptions of what can exist, it is fair to say that new data continue to throw unexpected light on current conceptions of phonological structure, and we are far from feeling confident that we know what we need to know. The current threat of extinction that looms over the stock of spoken languages makes the crucial role of field work all the more conspicuous. More so than in speech synthesis, advances in speech recognition have been possible without any appreciable contribution of phonological theory. This is because researchers have worked with pattern recognition techniques which are independent of the medium within which those patterns exist.