ASSIMILATION ACCORDING TO PETER ROACH

Assimilation according to Peter Roach

The device mentioned earlier that produces “mechanical speech” would contain all the words of English, each having been recorded in isolation. A significant difference in natural connected speech is the way that sounds belonging to one word can cause changes in sounds belonging to neighbouring words. Assuming that we know how the phonemes of a particular word would be realised when the word was pronounced in isolation, when we find a phoneme realised differently as a result of being near some other phoneme belonging to a neighbouring word we call this an instance of assimilation. Assimilation is something which varies in extent according to speaking rate and style; it is more likely to be found in rapid, casual speech and less likely in slow, careful speech. Sometimes the difference caused by assimilation is very noticeable, and sometimes it is very slight.Generally speaking, the cases that have most often been described are assimilations affecting consonants.

As an example, consider a case where two words are combined, the first of which ends with a final consonant (which we will call C^f) and second of which starts with a single initial consonant (which we will call Cⁱ); we can construct a diagram like this:

If C^f changes to become like Cⁱ in some way, the assimilation is called regresive (the phoneme that comes  first is affected by the one that comes after it); if Cⁱ changes to become like C^f  in some way, the assimilation is called progressive. In what ways can a consonant change? We have seen that the main differences between consonants are of three types:

i) differences in place of articulation

ii) differences in manner of articulation

iii) differences in voicing.

In parallel with this, we can identify assimilation of place, of manner and of voicing in consonants. Assimilation of places is most clearly observable in some cases where a final consonant (C^f) with alveolar place of articulation is followed by an initial consonant (Cⁱ) with a place of articulation that is not alveolar. For example, the final consonant in ‘that’ ðæt is alveolar t. In rapid, casual speech the t will become p before bilabial consonant, as in: ‘that person’ ðæp pɜːsn; ‘Light blue’ laɪp bluː; ‘meat pie’ miːp paɪ. Before a dental consonant, t will change to a dental plosive, for which the symbol is t, as in: ‘that thing’ ðæt θɪŋ;  ‘get those’ ɡet ðəʊz; ‘cut through; kʌt θruː. Before a velar consonant, the t will become k, as in: ‘that case’ ðæt keɪs; ‘bright colour’ braɪk kʌlə; ‘quite good’ kwaɪk ɡʊd. In similar contexts d would become b, d and g respectively, and n would become m, n and ŋ. However, the same is not true of the other alveolar consonants: s and z behave differently, the only noticeable change being that s becomes ʃ, and z becomes ʒ, when followed by ʃ or j, as in: ‘this shoe’ ðɪʃ ʃuː; ‘those years’ ðəʊʒ jɪəz. It is important to note that the consonants that have undergone assimilation have not dissapeared; in the above examples, the duration of the consonants remains more or less what one would expect for a two-consonant cluster. Assimilation of place is only noticeable in this regressive assimilation of alveolar consonants; it is not something that foreign learners need to learn to do.

Assimilation of manner is much less noticeable, and is only found in the most rapid and casual speech; generally speaking, the tendency is again for regressive assimilation and the change in the manner is most likely to be towards an “easier” consonant – one which makes less obstruction to the airflow. It is thus possible to find cases where a final plosive becomes a fricative or nasal (e.g. ‘that side’ ðæs saɪd, ‘good night ɡʊn naɪt), but most unlikely that a final fricative or nasal would become a plosive. In one particular case we find progressive assimilation of manner, when a word-initial ð follows a plosive or nasal at the end of a preceding word: it is very common to find that the Cⁱ becomes identical in manner to the C^f but with dental place of articulation. For example (the arrow symbol means “becomes”):

It seems that the ð phoneme frequently occurs with no discernible friction noise.

Assimilation of voice is also found, but again only in a limited way. Only regressive assimilation of voice is found across word boundaries, and then only of one type; since this matter is important for foreign learnes we will look at it in some detail. If C^f  is a lenis (i.e. “voiced”) consonant and Cⁱ is fortis (i.e. “voiceless”) we often find that the lenis consonant has no voicing; this is not a very noticeable case of assimilation, since, as we explained in Chapter 4, initial and final lenis consonants usually have little or no voicing anyway. When C^f is fortis (“voiceless”) and Cⁱ lenis (“voiced”), a context in which many languages C^f would become voiced, assimilation of voice never takes place; considering the following example: ‘I like that black dog’ aɪ laɪk ðæt blæk dɒɡ. It is typical of many foreign learners of English to allow regressive assimilation of voicing to change the final k of ‘like’ to g , the final t of ‘that’ to d and the final k of ‘black’ to g. This creates a very strong impression of foreign accent, and is something that should obviously be avoided.

Up to this point we have been looking at some fairly clear cases of assimilation across word boundaries. However, similar effects are also observable across morpheme boundaries and to some extent also within the morpheme. Sometimes in the latter case it seems that the assimilation is rather different from the word-boundary examples; for example, if in a syllable-final consonant cluster a nasal consonant precedes a plosive or a fricative in the same morpheme, the place of articulation of the nasal is always determined by the place of articulation of the other consonant; thus ‘bump’ bʌmp; ‘tenth’ tenθ; ‘hunt’ hʌnt; ‘bank’ bæŋk. It could be said that this assimilation had some “fixed” as part of the phonological structure of English syllables, since exceptions are almost non-existant. A similar example of a type of assimilation that has become fixed is the progressive assimilation of voice with the suffixes s and z; when a verb carries a third person singular ‘-s’ suffix, or a noun carries an ‘-s’ plural suffix or an ‘-‘-s’ possesive suffix, that suffix will be pronounced as S if the preceding consonant is fortis (“voiceless”) and as z if the preceding consonant is lenis (“voiced”), thus:

Much more could be said about assimilation, but from the point of view of learning or teaching English pronunciation, to do so would not be very useful. It is essentially a natural phenomenon that can be seen in any sort of complex physical activity, and the only important matter is to remember the restriction, specific to English, on voicing assimilation mentioned above.

Assimilation creates something of a problem for phoneme theory; when, for example, d in ‘good’ ɡʊd becomes g in the context ‘… girl’ (ɡʊg ɡɜːl) or b in the context ‘… boy’ (ɡʊb bɔɪ), should we say that one phoneme has been substituted for another? If we do this, how do we describe the assimilation in ‘good thing’, where d becomes dental d before the θ of ‘thing’, or in ‘good food’, where d becomes a labiodental plosive before the f in ‘food’? English has no dental or labiodental plosive phonemes, so in these cases, although there is a clearly assimilation, there could not be said to be a substitution of one phoneme for another. The alternative is to say that assimilation causes a phoneme to be realised by a different alophone; this would mean that, in the case of ɡʊg ɡɜːl and ɡʊb bɔɪ, the phoneme d of ‘good’ has velar and bilabial allophones. Traditionally, phonemes were supposed not to overlap in their allophones, so that the only plosives that could have allophones with billabial place of articulation were p and b; this restriction is no longer looked on as so important.

Here's a video that explains assimilation in a simpler way:
http://www.youtube.com/watch?&v=soywKZ4bm4U

Phonetic assimilation also occurs in spanish. For more information click the following link:
http://redalyc.uaemex.mx/pdf/602/60250101.pdf