Inconsistency in Child Phonology

Three types of inconsistency

In child phonology there are three types of inconsistency.

Different word positions

First, there is variable production of a particular phone (e.g., [f]), or a sound class (e.g., voiceless fricatives) in different word positions.

For example the child might produce /f/ word initially in ‘fun’ but replace with /p/ word finally (e.g., cup for cuff), and with /t/ within words (e.g., cottee for coffee).

This type of inconsistency is found in typical development, and in children with speech sound disorder.

The same word position

Second, we see variable production of a particular phone (e.g., [d]), or a sound class (e.g., voiced stops) in the same word position. For example, a child may use [d] and [b] interchangeably in the word initial position (with 'cubby' pronouced either 'cubby' or cuddy'). Alternatively they might say cuddy for cubby, cuggle for cuddle, and 'Toby' (correctly) for 'Toby'.

This type of inconsistency is seen in very young, typically developing children usually in the first 40 to 60 words they acquire. In some children a few of these early word productions will persist as frozen forms. For example, Jackson could say d-words but his ‘baby’ pronunciation of ‘dickie bird’ as /dɪkidɝd/ persisted until he was almost 6;0.

Multiple repetitions of the same word

The third type is variable production of a particular phone (e.g., [b]), or sound class (e.g., voiced stops) in multiple repetitions of the same word. This type of variability is sometimes referred to as ‘token-to-token variability’ (Seddoh, Robin, Sim, Hageman, Moon & Folkins, 1996).

This type is seen in children's speech sound disorders and is the defining characteristic of Inconsistent Speech Disorder (Dodd, 2005). This is the type of inconsistency tested in the DEAP inconsistency assessment.

Inconsistency Assessment

In the DEAP Inconsistency Assessment, 25 pictures are named three times in one session. Productions are compared to calculate an inconsistency score. Children are deemed to have Inconsistent Speech Disorder (in Dodd’s 2005 classification) if they have at least 40% of words produced variably. That is, if their token-to-token variability is 40% or greater. Children with at least two atypical patterns and inconsistency <40% are considered to have Consistent Speech Disorder (Holm, Crosbie & Dodd, 2007; Dodd, 2011).