Connected Speech and Coarticulation (27-Nov-2003)
Speech is a stream of sounds rather than a series of discrete segments
and in many cases the sounds merge or change, sometimes to anticipate the
next sound and sometimes by being affected by a previous sound.
Assimilation
Assimilation refers to the effect where one sound segment is modified by its
neighbour, and causes one sound becoming phonetically similar to the other.
E.g. in English, in the sentence "I have to", the "v" of "have" is devoiced
and is pronounced as an "f" since the first sound of the next segment is
devoiced. When one sound changes to become more like the next, this is
"regressive" assimilation; when one sound changes to become more like the
preceding sound, this is "progressive" assimilation. Crystal also notes
"coalescent", where two sounds mutually influence one another. Examples (from
Crystal p166):
- progressive : in "ten bikes", the "n" is pronounced as "m"
- regressive : in "lunch score", the "s" is pronounced "sh"
- coalescent : in "don't you", the center segment is pronounced
"ch"
Different languages exhibit different assimilatory rules. For example, in
French, "avec vu" is is articulated "aveg vu", with the "c" beooming voiced.
In Engish, anticipatory voicing does not happen so frequently, which is one of
the reasons why a French speaker of English may have a noticeable "accent" -
if he applies this kind of assimilation it will sound unusual to a native
speaker.
Assimilation can be of different kinds:
- with assimilation of voice, a sound becomes voiced or unvoiced to
match its neighbour, as in "I have to" where the "v" is devoiced
- with assimilation of place, the place of articulation of a
consonant changes to the same place as the adjacent one. Typically in
English this occurs with word-final alveolar consonants, e.g. "that boy" ->
"thap boy"
- with assimilation of manner, one sound changes the manner of
articulation to be more like its neighbour, Roach gives the example "get
some" changing to "gessome" - the "t" of get becomes like the "s" of
"some"
Note that the assimilation process appears to be resulting in different
phonemes being used, and so this ought to change the meaning of the words -
why it doesn't is something that will be covered another day. However these
assimilation rules are part of the phonology of the language, and so to a
native speaker they are just a natural part of speech.
Assimilation might be seen as "lazy" articulation, at any rate it seems to
be a result of trying to minimize the effort required.
Coarticulation
Coarticulation is related to assimilation; Roach says it's not easy to define.
It is to do with the fact that when speaking, many different articulatory
processes and components are involved, and these have different
characteristics (e.g. tongue can move faster than vocal folds), and do not
move discretely from one position to another, which means that certain aspects
of articulation can be blurred. Because it's more a physical process, it's
not something that can so easily be controlled, especially when speaking
quickly. And because it's a physical process, it's not a characteristic of a
language's phonology.
Anticipatory coarticulation occurs when one sound is affected by the
following sound; perseverative coarticulation is when one sound is affected by
the previous sound. In the word "screws", the /s/ and /z/ are articulated
with rounded lips, but in "sees", they're not.
Elision
Elision is the phenomenon where sound segments are omitted completely,
e.g. (from Crystal p166), "mashed potatoes" loses the "-ed" of "mashed". This
may be a kind of coarticulation: electropalatography can show that in saying
these words a speaker may, for example, move the tongue almost to the point
where a sound would be articulated, without quite managing it: in other words,
the sound is not deliberately omitted, it's just not given time to be made.
Useful book readings for this lecture:
- Roach: "Phonetics", ch. 8
- Crystal: "Encyclopedia of Language", p.166 (assimilation), p158 (coarticulation)
Sounds, Grammar and Meaning page