Assessing Speech Intelligibility and Severity

1. Assessing Speech Intelligibility and Severity What are some standard procedures?

2. Are measures of intelligibility and severity the same? • Although judgements about intelligibility and severity may be correlated, they represent two different indices about an individual’s speech • For example, a child may have a severe resonance disorder, but his/her speech is still intelligible

3. Intelligibility Scales • Typically a panel of 2-5 listeners (expert ~ novice; familiar ~ unfamiliar) rate a taped (audio or video) segment of child’s speech • Rank intelligibility of child’s speech compared to age peers • Scales typically use 3-point or 5-point judgment scales (See Bleile) • scores are averaged to derive a composite intelligibility rating score

4. Intelligibility Scales • Kent, Miolo, & Bloedel (1994) compared 19 intelligibility measures according to 5 categories that differed with regard to the emphasis of the analysis (phonetic ~ phonemic; word level ~ conversation)

5. Intelligibility Scales • Listed 8 factors that influence clinical evaluation of intelligibility: • loss of phonological contrasts • loss of contrasts in specific environments • extent of homonymy • amt of difference between target~realization • frequency of occurrence in English • consistency • familiarity of listener with speaker • context in which communication occurs

6. Intelligibility • Weston & Shriberg (1992) concluded that articulation variables alone cannot account for all the breakdowns that result in communication • other general contextual and linguistic variables are related to speech intelligibility

7. Severity • Similar to intelligibility rating scales, a panel of familiar or unfamiliar listeners judge a segment of a child’s recorded (audio or video-taped) speech (single word or connected speech)

8. Severity • Perceptual scales (see Bleile) or quantitative measures • 4 Point Clinical Judgement Scale of Severity • No disorder-Mild-Moderate-Severe • average score of 3.5 often required to provide clinical services

9. Severity • Quantitative Measures • PCC (and 8 variations) • Hodson’s PDS • Edwards’ PDI

10. PCC Mild >90% Mild-Mod 65-85% Mod-Sev 50-65% Severe <50% PDS Mild 1-19 pts Moderate 20-39 Severe 40-59 Profound 60+ Comparison of PCC and PDS Severity Ratings

11. Shriberg, Austin, Lewis, McSweeny, & Wilson (1997) 9 speech metrics PCC (based on conv speech) PCC-A (common clinical distortions scored correct) PCC-R ([un]common distortion scored correct) ACI (differentially weighs distortion ~ sub/omis) PCI (percentage of sounds mastered-early talkers) PVC (similar to PCC, but for vowels/diphthongs) PVC-R (similar to PCC-R, but for vowels/diphthongs) PPC (percentage to consonants/vowels correct) PPC-R (scores distortions correct)

12. Which metric is most appropriate? Depends on specific needs of the assessment • Interest limited to consonants • PCC, PCC-A, PCC-R, ACI • Young/severely delayed children • PCI • Interest in vowels/diphthongs • PVC, PVC-R • Interest in articulation competence on all speech sounds • PPC, PPC-R

13. Rafaat, Rvachew, & Russell (1995) • Purpose of study was to determine the percentage of agreement between SLPs in rating PI severity • Adequate reliability for older children (4;6+), but unreliable for children under 3;6 • Unable to reliably distinguish TD from mild delay

14. Why were SLPs less reliable on severity ratings of younger children?

15. What factors account for differences in reliability ratings?