Speech intelligibility refers to how well someone understands a verbal message. Usually, this measure is taken from assessment conducted in a controlled or quiet environment. However, in functional real-world communication exchanges, many factors influence speech intelligibility. These factors could relate to:
- the speaker (articulation errors, accent, mumbling, not facing the listener, etc)
- the listener (familiarity with speaker, experience with or access to spoken language, alertness, etc)
- the context (background knowledge of the conversation topic, the kind of language that is used, etc.)
- the environment (background noise, lighting, distractions, physical barriers like wearing masks, etc.)
This idea is highlighted by the term "comprehensibility" which is "the extent to which a listener understands utterances produced by a speaker in a communication context" (Barefoot et al., 1993). "Comprehensibility" is not an interchangeable term that replaces "intelligibility", but when supporting Deaf and Hard-of-hearing (Hoh) students with speech intelligibility goals, we must consider all factors impacting it. Following an adult model, we work with students to determine what factors have the biggest impact on their communication. This method promotes self-awareness and the ability to assess pros/cons of certain communication environments for speaking tasks.
It should be noted that many Deaf and Hoh students may have reduced phonological awareness due to limited exposure to spoken language, language deprivation, or reduced access to sound. Often, speech language pathologists can incorporate phonological awareness into assessments and treatments to support overall development of the phonological system.
Additionally, one should consider students’ experience with voicing and spoken communication. Deaf and Hoh students who are new to using spoken communication may experience difficulty with the physiological aspects of voice, including:
- Coordinating respiration for breathing and speech
- Control of air expenditure
- Modulation and awareness of pitch, volume, and voice onset
- Resonance
Assessment may include standardized tests, but because those are not normed on the Deaf/Hoh population, assessment may reflect a more dynamic approach. Parts of standardized measure may be used as supplemental material in a dynamic assessment.
Word Level
Assessment at the word level looks at a student’s ability to produce sounds of words in isolation. We assess for any articulatory or phonological error patterns present to create speech sound targets which will have the greatest impact on the student’s overall intelligibility. Using a variety of criterion referenced and norm referenced testing, we observe phoneme production in various linguistic contexts. Evaluating for stimulability of sounds given visual, tactile, or verbal cues may also be implemented at this stage of assessment.
It is helpful to assess the articulatory productions of words that incorporate each consonant and vowel phoneme in the initial, medial, and final positions of the word, as appropriate depending on second language influences. A well-rounded articulation assessment at the word level should indicate sound production errors while also highlighting error patterns involving distinctive features of speech. We have found that describing errors to students using a distinctive feature approach (place, manner, and voicing) is valuable when discussing results of assessment with students.
Phrase and Sentence Level
Assessing intelligibility at the phrase and sentence level allows us to compare if misarticulations occur across tasks varying in linguistic complexity (happen only at the word level or at both the word and phrase/sentence levels). Articulatory and phonological error patterns at this level can negatively impact functional communication for a student.
Errors may also vary depending on if stimuli that are presented are within context of a specific topic (e.g., everyday phrases, sentences about school) or out of context random phrases or sentences.
Conversation/Discourse Level
Intelligibility and comprehensibility could be assessed at the discourse level through analyses of conversation speech or read speech. At the discourse level, you gain insight on articulation but also a speaker’s vocal quality and use of suprasegementals during running speech.
When analyzing conversation samples, cultural competence should be practiced. Refer to the list at the top of this page that describes factors that impact a person’s ability to understand a speaker.
Read-aloud discourse can be an alternative to a conversation sample because reading reduces cognitive load by eliminating language formulation for the speaker. The student can focus more attention on the mechanics of voicing like ongoing coordination of respiration, phonation, and articulation while integrating sound-symbol correspondence and phonological awareness skills required for read-aloud speech.
If both types of discourse levels are completed, compare performance across both tasks.