Metric	Definition
Consonant and vowel segments with phonemic errors	Calculated via the phonemic edit distance based on target and produced phoneme strings (Smith et al., 2019), expressed as percent. Obtained for the motor speech examination sample.
Words with phonemic errors	Percent words produced with one or more phoneme errors. Obtained for all three speech samples.
Words with distortion errors	Percent words produced with one or more distortion error/s. Obtained for all three speech samples.
Words with distorted substitution errors	Percent words produced with one or more distorted substitution error (i.e., produced with one or more sound segments that were simultaneously coded as a phonemic and distortion error). Obtained for all three speech samples.
Word syllable duration	Mean duration in ms for syllables in words produced with three or more syllables, calculated by dividing the duration of the word by the number of produced syllables (Haley et al., 2012). Obtained for all three speech samples.
Narrative syllable duration	Mean duration in ms for all syllables within one analysis group. Analysis group duration was divided by the number of produced syllables and averaged within each sample. Obtained for the two connected speech samples.
Pairwise variability index	The normalized duration difference in syllable duration between adjacent syllables. For the motor speech examination, it was restricted to two unstressed–stressed syllable sequences (Ballard et al., 2014), and for the connected speech samples, we calculated the average across all adjacent pairs in each analysis group. Obtained for all speech samples. $\mathrm{PVI}=100\left(\frac{\mathrm{d}1-\mathrm{d}2}{\left(\mathrm{d}1+\mathrm{d}2\right)/2}\right)$
Scanning index	Determined for words (in the motor speech examination) or analysis groups (in the connected speech samples) that were produced with four or more syllables. We calculated the product of syllable durations divided by the mean syllable duration raised to the nth power (Ackermann & Hertrich, 1993) and averaged these values across words/analysis groups for each of the three speech samples. $\mathrm{SI}=\frac{{\prod }_i^n{s}_i}{{\left(\frac{{\sum }_i^n{s}_i}{n}\right)}^n}$

Note. Pairwise variability index: d1 is the stressed syllable duration from onset of one syllable to onset of the next (ms) when applied to individual words and the first syllable duration when applied to connected speech. Note that use of the syllable duration in the calculation deviates from other studies, which have used the syllable nucleus (e.g., Ballard et al., 2014). Scanning index: s_i is syllable duration (ms), ∏ is the series of products, ∑ is the series of sums of syllable durations, and n is number of syllables.