What percentage of speech phonemes can typically be seen on the lips?

The correct percentage of speech phonemes that can typically be seen on the lips is 40%. This figure is grounded in the recognition that not all sounds produced during speech are visually discernible. Many phonemes, particularly those involving sounds made with the tongue or throat, are not visible on the lips.

Speech involves a complex combination of vocal sounds, some of which are produced in ways that do not lend themselves to visual interpretation through lip movements. The sounds that can be observed—consonants and vowels—represent around 40% of the phonemes in spoken language. This means that visual cues from lip movements can significantly aid in speech reading, but they only provide partial information since many sounds require additional auditory cues to fully understand speech. Thus, the ability to lip-read is limited to around 40% of the phonemes, reinforcing the importance of combining visual and auditory information for effective communication, especially for individuals who are deaf or hard of hearing.