Sonority Sequencing Principle for Clusters

Research has demonstrated that it is most efficacious to treat three-element clusters to effect change throughout a child's system (if the child has the second and third consonants in his/her system already). For example, if a child is taught /spl-/, then he/she should already have /p/ and /l/ in his/her repertoire. If the child has an impoverished system, this would not work.

However, there has been some exciting research that would be applicable to these students and others who have difficulty with clusters. The Sonority Sequencing Principle was identified in linguistics research during the last 20 years or so. It dictates that onsets (word-initial sounds) must rise in sonority and codas (ending sounds) must fall in sonority. Sonority is the inherent loudness of sounds relative to one another. The greater the sonority, the wider the mouth is and the more vowel-like a sound is (Barlow, 2000). Linguists have identified the relative sonority for different sound classes. In 1990, Steraide assigned values to each sound class, which are indicated in parentheses. The most sonorous sounds are vowels (0), followed by glides (1), liquids (2), nasals (3), voiced fricatives (4), voiceless fricatives (5), voiced stops (6) and voiceless stops (7).

In 1999, Gierut applied this principle to treatment. She identified an implicational relationship between clusters with small sonority differences and clusters with large sonority differences. If a child's system had clusters with small sonority differences, that implied the presence of clusters with a large sonority difference. For example, the cluster /sn-/ has a small difference (voiced fricative Steraide's value of 4) - nasal (value of 2)) of 2. The cluster /kw-/ has a large difference of 6 (voiceless stop (value of 7) - glide (value of 1)). Therefore, the cluster /sn-/ is considered to be more complex and marked relative to /kw-/.

The attached document (Sonority Sequencing Principle for Clusters) identifies the sonority difference between clusters. Research has suggested that it is most efficacious to teach clusters with a small sonority difference, such as /sn-/, /sm-/, /fl-/, /fr-/, etc., to create change in a child's system. One caveat is to avoid teaching /sp-/, /sk-/ and /st-/ because they violate the Sonority Sequencing Principle, resulting in a difference of -2. Furthermore, Gierut and her colleagues found that teaching these three fricative + stop clusters inhibited generalization to other clusters. Linguists do not consider /sp-/, /sk-/ and /st-/ to be true clusters. Please see the attached document (Sonority Sequencing Principle for Clusters) for the values of each cluster. If you teach the most complex clusters, you will see the child acquire the less complex clusters without direct treatment.

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