Computer display of vowel quadrilateral with real-time representation of articulation

The classical characterisation of vowel sounds used by phoneticians is the vowel quadrilateral, which originally was assumed to be the locus of the tongue body between its four extreme vowel positions. A method of real-time computer analysis and display which represents the vowel quadrilateral is described. This has application in computer-based speech training aids, but may have wider use in speech research generally.