The concept of speech intelligibility is relevant to several fields, including phonetics, human factors, acoustical engineering, and audiometry.
Humans alter the way they speak and hear according to many factors, like the age, gender, native language and social relationship between talker and listener.
How well a spoken message can be understood in a room is influenced by the Intelligibility is negatively impacted by background noise and too much reverberation.
[4] The fact that background noise compromises intelligibility is exploited in audiometric testing involving spoken speech and some linguistic perception experiments as a way to compensate for the ceiling effect by making listening tasks more difficult.
[5] The human brain automatically changes speech made in noise through a process called the Lombard effect.
It involves modifying the formants F1 and F2 of phonetic vowel targets to ease perceived difficulties on the part of the listener in recovering information from the acoustic signal.