The human dependency on formants forvocal production is argued to be one of the most important domain-specificqualities of speech.
Fitch (2000: 260) states that humans have an ‘unusuallyheavy use of formants’. The use of the word ‘unusually’ is taken to suggestthat nonhuman primates in their vocalisations do not make frequent use offormant frequencies as humans do. This argument is further supported byLieberman (1968: 1580) who states that nonhuman primates do not appear tomanipulate the supralaryngeal vocal tract in the way that humans do. This wouldsuggest that in nonhuman primates the use of formants is not found due tolimited manipulation of the supralaryngeal vocal tract. However, more recentstudies have found that non-human primates do make use of formants but not tothe large extent at which humans do (Taylor and Reby 2010: 221). From this itcan be seen that the dependency for formant use is domain-specific to humanspeech. A reliance on formants for vocalproduction means that the vocal tract must be adaptable.
This is so that it canproduce the wide range of shapes and lengths needed for producing distinctphonemes through different formant frequencies. This is possible due largely tothe evolutionary changes that occurred to the vocal tract morphology. 2.2Vocal Tracts MorphologyThe vocal tract in humans today canproduce a wide variety of speech sounds. This ability is notably a result ofthe vocal tract morphology and its ability to produce distinct formantfrequencies.
The best way to explore the evolutionary changes in vocal tractmorphology is to examine how the human vocal tract differs from that ofnon-human primates, our closest living ancestors. One of the key differencesbetween the vocal tract morphology of nonhuman primates and humans is theheight of the larynx and the shape of the tongue. The larynx in humans restsmuch lower than the larynx of nonhuman primates (Fitch 2000: 260). This is dueto a process in childhood development whereby the tongue lowers in the neck andwith it so does the larynx (Lieberman 2007: 46). The lowered larynx leads to atwo tube configuration of the vocal tract in humans.
The first of the two tubesis the oral cavity which is common to humans and all nonhuman primates, thesecond tube is pharyngeal cavity – where the larynx is based within the