locus (n.)

A term used in ACOUSTIC PHONETICS to refer to the apparent point of origin of a FORMANT for a given PLACE OF ARTICULATION, as displayed on a SPECTROGRAM. The formants which identify VOWELS are bent in characteristic directions, depending on the CONSONANTS adjacent to them; but for any single consonant these bends, or TRANSITIONS, all point in the same direction, at a hypothetical natural frequency range for the consonant. It is this hypothetical point of origin which is referred to as the locus (or, in later work, locus space) of the consonant. A locus equation is based on the onset FREQUENCY of the second formant and the steady-state value of that formant during the vowel in a consonant–vowel sequence. A linear regression is performed on these two variables for productions of the same consonant in different vowel contexts. The slope of the locus equation can be associated with the degree of COARTICULATION between the consonant and the vowel: a slope of 1 indicates maximum coarticulation (i.e. the onset and target frequencies of the second formant would be identical); a slope of 0 indicates no coarticulation.