Linguistics 105 * Words and Sounds
Lecture Number Six-a
On the Road from the Brain to the Tongue

If two linguistic sounds are not distinct phonemes in a language; that is, if they are allophones of the same phoneme, they are related to the phoneme by rule. These PHONOLOGICAL RULES represent regular changes that occur between the brain and the articulatory organs, since a phoneme is, more or less, what we think we are saying while the allophone is what we actually say. That is, the sounds of words are stored in the brain as sequences of phonemes. Allophones are how we actually pronounce phonemes when we speak.

The reason for the disparity between how a sound is stored in the brain and how it is pronounced is COARTICULATION, the fact that sounds are not pronounced in strict sequences but in clusters. Say quiet ([kwajt]) very slowly. Notice that you round your lips for the [w] simultaneous to raising the back of your tongue to pronounce the velar [k]. This means that any given phonemes pronunciation may be affected by the sounds which surround them, the CONTEXT or CONDITIONS in which they occur. Phonology studies the effects of neighboring sounds on phonemes and compares them across languages.

When discussing coarticulation or phonological rules it is important to consider DISTINCTIVE FEATURES of phones, and sometimes to determine a NATURAL CLASS. For example, we know that in English, the group of phones we represent by /p b t d k g ´/ are stops. Within this group, /p t k ´/ are voiceless, as are, for example fricatives /f/ and /s/. The stops /p b/ can also be called bilabial, and in this case the are grouped with /m/ as a natural class of English bilabials. (In feature notation, this is represented C [+labial]).

  1. Assimilation

    The most common effect of an adjacent sound on a phoneme is called ASSIMILATION. Assimilation means that one of the sounds becomes more like the other one. You could also consider assimilation as the absorption of a feature from an adjacent segment. Here are some examples:

    1. Nasal Consonants

      Nasals are notorius for assuming the place of articulation of consonants which follow them. In English a voiced alveolar nasal /n/ becomes voiced bilabial nasal [m] before bilabials. Before velars, voiced alveolar nasal /n/ becomesa voiced velar nasal [].

    2. You need a Java-enabled web browser!

      Sometimes spelling follows pronunciation:

      implausible [mplzb]
      immutable [mjutb]
      improper [mprap]
      imperfect [mpfkt]

      but not always; the following words exhibit assimilation when spoken quickly.

      incorrect [krkt]
      incongruent [kagruwt]
      incapable [kepb


    3. Vowel Assimilation
    4. Vowels are also susceptible to assimilation. In fact, they frequently assimilate the feature [+Nasal] from consonants which follow them.

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      If you listen carefully, you can pronounce [pt] and [pn], dropping the final consonant, and hear the difference between the two consonants. Here are some more:

      ton [tςn]
      tune [tjun]
      tan [tn]
      tone [ton]

  2. Phonological Rules

    It is easy to see what happens when a phonological rule creates an allophone from a phoneme. The next question is how to we express these changes, maintaining the precision of description offered by phonetic symbols and features. Since most phonological rules affect features, our rules must be based on them; although, if a rule affects an entire phoneme, we must be able to express that, too.

    The basic principle is that an allophonic rule describes the addition, deletion, or replacement of a feature of one phoneme when it is adjacent to another. The second phoneme, that causes the change, is called the CONTEXT or CONDITION of the rule. The rule for vowel nasality assimilation discussed abot would be the following:

    [+Vowel] [+Vowel] / ______ [+Nasal]
    [-Nasal]   [+Nasal]      

    Reading this rule is very simple. It says that a segment standing in the position of the underline and which is a vowel ([+Vowel]), must change its nasality to [+Nasal] if a segment with [+Nasal] follows it.

    The rule which deletes the aspiration of English voiceless stops would look like this:

    [+Aspiration] [-Aspiration] / [s] ______
    [+Stop]   [+Stop]      

    All the symbols you will need to write phonological rules may be found on this short page.

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©1997 | Robert Beard