Lipreading Myth 3: only 30% ?

Almost all publications about lipreading say that lipreaders 'get' only 30% of the information that hearing people do. Lipreaders have to guess the missing 70%, which makes lipreading so very difficult and demanding. 

The bad news: yes, lipreading is very difficult and demanding.

The good news: the 30% rule may be true in (some) experimental conditions, but has no predictive value for real life.

Where does the 30% come from? 

Spoken English uses approximately 44 different phonemes (http://en.wikipedia.org/wiki/Phonemes_of_English). When you present these in isolation or in short (meaningless or meaningful) words without sound, subjects can discriminate appr. 12 different 'visemes' = phoneme groups.

For the lipreader, some phonemes are indistinguishable. The usual example is 'b - p - m': 3 different phonemes that look exactly the same to the lipreader. Words like 'pat', 'bat', 'mat' cannot be distinguished by lipreading.

Other phonemes invisible and cannot be seen at all: 'cate', 'gate', 'hate' all look like 'ate'. 

Depending on the research conditions, the speaker, and the subjects, a lipreader of English can see 5 different vowel groups, and 7 different consonant groups. These groups are sometimes called 'visemes'. English has 44 different auditory distinguishable phonemes, and only appr. 12 visually distinguishable visemes (but numbers and groupings vary, depending on the methods, speakers, etc.). So: lipreaders 'do it' with 30% of the information. 

But!

In everyday life, people do not speak in single, one syllable words. Well OK, some people do: 'Hi', 'yes', 'nope', 'wow', 'bye'.

But not without context! Someone is leaving and says 'bye'. The lipreader sees something that could be 'pie', 'my', or 'bye'. Does he or she have to guess 3 times, before s/he gets the right answer? Eh... no? 

Plus

• Longer words are easier to lipread than one syllbale words, because longer words have fewer 'look-a-likes'. Without context, it will be difficult to guess 'bye' correctly. 'See you later' (not one word? OK, not in writing, but in spoken language it looks like one word!) has fewer look-a-likes and is easy to recognize, especially in the context of someone leaving. Invisible or indistinguishable phonemes can be identified 100% correct in the context of a meaningful word. Context helps! 
• Some speakers articulate so clearly, that you CAN see the difference between 'P' and 'B'. Other speakers on the other hand, barely open their mouths. All you see is 'open - closed - open - closed'. With a good 'lipspeakers', a lipreader may get 100% of the information. A bad lipspeakers: 0% + a lot of frustration! 
• You don't need all the phonemes, to get all the information! Even hearing people don't hear all phonemes correctly, their brains automatically fill in the gaps. Texters don't need all letters to understand each other, they can use abbeviations like FBOW (for better or worse), ATB (all the best), and many others. Texters get only ... 20% of the information that old fashioned writers get? No. They get maybe 20% of the letters, but experienced texters can get 100% of the information! 
• In the context of a sentence, even invisible ..... can be guessed! Of course, to be able to use context, you need foreknowledge of the language, the speaker and the topic...  

The moral of the story:

Yes, lipreading is difficult. Yes, lipreaders have to do it with information that has many more 'gaps', than hearing people do. But foreknowledge and context can help you fill in many of the gaps!

And no, lipreaders should not be afraid to make mistakes. Few speakers are 100% predictable. And those who are, are often boring...