Table 2.

The 12 Parameters Comprising the IVD Score

Rhythm/syllabicity
1	Voiced: Pitch detectable for 50% SVI	Positive classification on these parameters suggests that vocalizations tended to show voicing features, canonical formant transitions, and spectral entropy variations consistent with speech-like rhythm and syllabicity.
2	Canonical Syllable: Formant transitions < 120 ms
3	Spectral entropy typical of speech
Squeal quality (low spectral tilt and high pitch control)
4	Mean pitch high (squeal): > 600 Hz	Positive classification on these parameters suggests more active expression in the high spectral frequency range (i.e., a squeal quality to vocal productions).
5	Low spectral tilt
6	High-frequency energy concentration
Growl quality (wide format bandwidth and low pitch control)
7	Mean pitch low (growl): < 250 Hz	Positive classification on these parameters suggests more active expression in the low spectral frequency range (i.e., a growl quality to vocal productions).
8	Wide bandwidth (first two formants)
Duration of SVIs within utterances
9	Short (110–250 ms)	Positive classification on parameters nine and ten suggests speech-like rhythmic organization because duration values are typical of syllables in adult speech. Positive classification on parameters 11 and 12 suggest the opposite because the corresponding durations are beyond the range of typical syllables.
10	Medium (250–600 ms)
11	Long (600–900 ms)
12	Extra long (900–3000 ms)

Note. SVI = speech-related vocal island. Table adapted from Oller et al. [2010]. Copyright [2010] held by Oller et al. Adapted with permission.