Comprehensibility

At the simplest level, comprehensibility is defined as “the extent to which a listener can understand (comprehend) a spoken utterance in a communicative context.” This entry discusses three levels of speech production in conjunction with Stephen Camarata and Paul Yoder’s definition of comprehensibility as “understandable spoken language.” The first level is speech accuracy, or the extent to which individual target phonemes are correctly produced within a word. The second level is speech intelligibility, which is the extent to which an utterance can be understood when the intended message is known. The third and most functional level is speech comprehensibility, the extent to which a listener understands spoken messages in “real-world” speaking situations with the goal of communicating information to the listener(s).

These basic distinctions have been described and applied within the adult speech disorders literature for conditions such as dysarthria and apraxia for more than two decades. For example, intelligibility can be defined as the degree to which listeners transcribe or identify phonemes and words in passages that have been read by a speaker with dysarthria, a motor speech disorder. In contrast, comprehensibility is viewed within the context of the World Health Organization framework for understanding disability and is a measure of the extent to which the speaker can effectively communicate in social contexts within the limitations of speech disability. This definition should also be considered within the context of the place of speech production within the broader context of expressive language.

A basic goal of communication is to transfer information from one person to another or to a group of listeners. If language is defined as a code for conveying ideas, then an important part of that code is speech, which is the meaningful verbal units of communication. Speech, in turn, consists of phonemes, which are the minimal meaningful units of speech. Words are a combination of phonemes (also known as speech sounds). For example, the word boat includes three phonemes: /b/, /o/, and /t/. If a different phoneme is used in the final position, this changes the meaning of the word; boat becomes bone /b/, /o/, /n/. Phonemes are assembled into words (lexemes) and ultimately, into larger communication units such as phrases and sentences.