Paralanguage, also known as vocalics, is a component of meta-communication that may modify meaning, give nuanced meaning, or convey emotion, by using techniques such as prosody, pitch, volume, intonation, etc. It is sometimes defined as relating to nonphonemic properties only. Paralanguage may be expressed consciously or unconsciously.
The study of paralanguage is known as paralinguistics and was invented by George L. Trager in the 1950s, while he was working at the Foreign Service Institute of the U.S. Department of State. His colleagues at the time included Henry Lee Smith, Charles F. Hockett (working with him on using descriptive linguistics as a model for paralanguage), Edward T. Hall developing proxemics, and Ray Birdwhistell developing kinesics. Trager published his conclusions in 1958, 1960 and 1961.
His work has served as a basis for all later research, especially those investigating the relationship between paralanguage and culture (since paralanguage is learned, it differs by language and culture). A good example is the work of John J. Gumperz on language and social identity, which specifically describes paralinguistic differences between participants in intercultural interactions. The film Gumperz made for BBC in 1982, Multiracial Britain: Cross talk, does a particularly good job of demonstrating cultural differences in paralanguage and their impact on relationships.
Paralinguistic information, because it is phenomenal, belongs to the external speech signal (Ferdinand de Saussure's parole) but not to the arbitrary conmodality. Even vocal language has some paralinguistic as well as linguistic properties that can be seen (lip reading, McGurk effect), and even felt, e.g. by the Tadoma method.
Aspects of the speech signal
Perspectival aspects
Speech signals arrive at a listener's ears with acoustic properties that may allow listeners to identify location of the speaker (sensing distance and direction, for example). Sound localization functions in a similar way also for non-speech sounds. The perspectival aspects of lip reading are more obvious and have more drastic effects when head turning is involved.
Organic aspects
The speech organs of different speakers differ in size. As children grow up, their organs of speech become larger, and there are differences between male and female adults. The differences concern not only size, but also proportions. They affect the pitch of the voice and to a substantial extent also the formant frequencies, which characterize the different speech sounds. The organic quality of speech has a communicative function in a restricted sense, since it is merely informative about the speaker. It will be expressed independently of the speaker's intention.
Expressive aspects
Paralinguistic cues such as loudness, rate, pitch, pitch contour, and to some extent formant frequencies of an utterance, contribute to the emotive or attitudinal quality of an utterance. Typically, attitudes are expressed intentionally and emotions without intention, but attempts to fake or to hide emotions are not unusual.
Consequently, paralinguistic cues relating to expression have a moderate effect of semantic marking. That is, a message may be made more or less coherent by adjusting its expressive presentation. For instance, upon hearing an utterance such as "I drink a glass of wine every night before I go to sleep" is coherent when made by a speaker identified as an adult, but registers a small semantic anomaly when made by a speaker identified as a child. This anomaly is significant enough to be measured through electroencephalography, as an N400. Autistic individuals have a reduced sensitivity to this and similar effects.
Emotional tone of voice, itself paralinguistic information, has been shown to affect the resolution of lexical ambiguity. Some words have homophonous partners; some of these homophones appear to have an implicit emotive quality, for instance, the sad "die" contrasted with the neutral "dye"; uttering the sound /dai/ in a sad tone of voice can result in a listener writing the former word significantly more often than if the word is uttered in a neutral tone.
Linguistic aspects
Ordinary phonetic transcriptions of utterances reflect only the linguistically informative quality. The problem of how listeners factor out the linguistically informative quality from speech signals is a topic of current research.