spoken speech and some linguistic perception experiments as a way to compensate for the ceiling effect by making listening tasks more difficult. Intelligibility standards Word articulation remains high even when only 1–2% of the wave is unaffected by distortion. Intelligibility with different types of speech Lombard speech The human brain automatically changes speech made in noise through a process called the Lombard effect. Such speech has increased intelligibility compared to normal speech. It is not only louder but the frequencies of its phonetic fundamental are increased and the durations of its vowels are prolonged. People also tend to make more noticeable facial movements. Screaming Shouted speech is less intelligible than Lombard speech because increased vocal energy produces decreased phonetic information. However, "infinite peak clipping of shouted speech makes it almost as intelligible as normal speech." Clear speech Clear speech is used when talking to a person with a hearing impairment. It is characterized by a slower speaking rate, more and longer pauses, elevated speech intensity, increased word duration, "targeted" vowel formants, increased consonant intensity compared to adjacent vowels, and a number of phonological changes (including fewer reduced vowels and more released stop bursts). Infant-directed speech Infant-directed speech—or baby talk—uses a simplified syntax and a small and easier-to-understand vocabulary than speech directed to adults Compared to adult directed speech, it has a higher fundamental frequency, exaggerated pitch range, and slower rate. Citation speech Citation speech occurs when people engage self-consciously in spoken language research. It has a slower tempo and fewer connected speech processes (e.g., shortening of nuclear vowels, devoicing of word-final consonants) than normal speech. Hyperspace speech Hyperspace speech, also known as the hyperspace effect, occurs when people are misled about the presence of environment noise. It involves modifying the F1 and F2 of phonetic vowel targets to ease perceived difficulties on the part of the listener in recovering information from the acoustic signal. Notes External links Intelligibility conversion ALcons to STI and vice versa Speech Quality and Evaluation (a chapter from a Master Thesis) Sound Hearing Interpersonal communication