Chapter 3.2 Speech Communication Human Performance Engineering Robert W. Bailey, Ph.D. Third Edition

The Designer’s Responsibility to know: Where The Frequency and Types Why The Content The Conditions The Consequences

The Speech Communication Chain Speech communication can be degraded if there are difficulties with the speaker, transmission of sound waves, or the listener. Designer has no control over speech errors. Some control that the speech content will be audible, distinguishable, & understood.

Sound and Noise In human terms, noise is unwanted sound.

Design Implications: *Human performance can be degraded under noisy conditions and can even result in permanent hearing disability. *Human performance depends on the ability to distinguish a desired sound (signal) from an undesired sound (noise).

Signal to Noise Ratio S/N = A measure of the relative sound intensity of the signal or speech, to the background noise. Example: If the average intensity of speech is 75 DB and the average intensity of the noise in which the speech is spoken is 70DB, the S/N ratio = +5DB. Speech, 60DB; Noise 60DB; S/N= Speech, 50DB; Noise 80DB; S/N=

Study by Miller & Nicely Consonants against a background of random noise. S/N = -18 DB, All consonants were confused with one another. S/N= -12 DB, Consonants M,N,D,G,B,V,Z conf. T,K,P,F,S were confused S/N = -6 DB, M&N were confused S/N = 0 DB, Certain individual consonants S/N =12 DB, All consonants distinguished.

Speech Loudness and Quality Subjective judgments made by users of speech transmission systems. People communicating by radio evaluate each other’s transmission, using a 5 point rating scale. “I read you loud and clear, your signal is 5 by 5.”

Speech Quality is Evaluated by Two Methods: A subject is asked to compare two transmissions A subject is asked to make a category judgment of a speech signal (I.E. Excellent, Good, Fair, Poor, or Unsatisfactory)

Speech Intelligibility The ability to recognize correctly the speech sounds when spoken.

Articulation Testing Ways to measure intelligibility. It involves using a group of highly trained listeners who transcribe what they hear How can we improve hearing where noise is a problem?

Speech or Hearing Limitations During the design stage of system development, the designer should have produced a Statement of Minimum Qualifications (SMQ) How many different languages are there in the world?

Language Problems 3000 different languages in the world. This creates particular problems in international systems such as air traffic control. # # # # # # # # is the world’s most common first and second language. # # # # # # # # is the language of international air traffic control. Accent is a problem. Variation in word usage (U.S. VS. Ireland). Regional dialects within countries.

Face to Face Speech Audibility For satisfactory communication, the speech level should exceed the noise level by at least 6 DB.

Language Considerations Noise Levels Number and types of verbal exchanges Maybe special hand signals are required

Matching Expectations and Message In any given situation, we call up the “Educated Expectation” or Schema we think is most appropriate for the particular activity. The schema helps us understand the message.

Vocabulary Size One way to increase the intelligibility of a message is to # # # # # # the size of the vocabulary. If the number of words is kept # # # # # #, and the entire list of these words is known to both the listener and the talker, the chances of accurately communicating are greatly increased.

Familiarity and Length of Words The more familiar-> ?????? The longer the word-> ??????

Word Context It is ?????? to understand a word heard in isolation then if it is heard in a sentence.