Why /i a u/ and /B D G/ ? Or why such an extremist evolutionary recurring trend
in speech sound systems?

Christian Abry, Jean-Luc Schwartz, Louis-Jean Boë,
Institut de la Communication Parlee, INPG-Universite Stendhal, Grenoble, France

email: abry@icp.inpg.fr

In the world language databases (Maddieson, 1986), /B D G/ are the most
prevalent places for consonants, as are the point vowels /i a u/. 
Jakobson, Fant and Halle (1952) conceived acoustically these places in
parallel with the vowels, as a triangular representation, until Chomsky
and Halle (1968) switched to articulatory features.  Lindblom's (1986)
and our endeavor rests on an acoustic space for vowel systems
computational prediction.  Up to recently it was not conceived of
consonant systems (say syllable onsets *) as implicating the same
principles as for vowels.  It is now possible to show that /i a u/ for
vowels and /B D G/ for consonants follow the same maximal dispersion
trend.  Labial, coronal and dorsal onsets are optimally distant
auditorily, while other features like retroflexion or pharyngealization
use only secondary dimensions (as e.g.  for vowels nasality and length). 
One must keep in mind that there is no in principle reason for not
having less extreme exemplars of vowel types in very small numbered
systems, where the auditory distinctiveness has not need to keep such
extreme vowels apart.  But a spacing like /e a o/ is not what is
generally observed for inventories as small as 3 vowels: /i a u/
instead.  It seems however that a significant proportion of Australian
languages do not display such extreme prototypes (Butcher 1994).  But
this question can be reconsidered in the light of old and new
observations: that is by factoring out coronal consonant secondary types
(retroflexion...) coarticulatory influence; and by taking into account
the possibility of producing occurrences of extreme types in
informational prosodic conditions (Fletcher, Butcher, 2003).  The answer
to this recurring extreme trend lies in our Dispersion-Focalization
Theory (Schwartz et al., 1997).  DFT allows to predict vowel systems
thanks to a competition between two perceptual costs: (i) dispersion
based on inter-vowel distances, (ii) local focalization based on
intra-vowel spectral salience related to formants proximity.  The first
one is related to the global structure of the system and the second to
the internal structure of each vowel element.  The DFT predictions fit
quite well with the phonological inventories being compatible with
preferred 3-to-7 vowels systems, and also with the possible variants in
the systems and in which order they can appear.  In DFT /i a u/ are
focal vowels, that is objects which are not only far away but also
intrinsically well formed perceptually and memorily, whatever the
articulatory costs for maintaining easy or difficult controls, reputedly
easy for /a/ and /u/, and typically difficult for /i/.  The same
framework has been demonstrated to work for consonants (Abry, 2003), in
a dynamic F2-F3 Consonant-Place-Space (CPS) in continuity with the
classical Vowel-Position-Space (VPS).  What could then be the
differentiation process, i.e.  the genesis of the workspaces for
consonants and vowels in this common framework of auditory coordinates?
We propose a developmental scenario for speech sound systems ontogenesis
- from canonical babbling (MacNeilage, Davis, 2001) to the emergence of
coarticulation - suggesting implications for the phylogenesis of speech. 

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* In a first generalisation, considering that CV is the universal
syllabic frame, consonants are simply considered here as syllable onsets
and vowels as syllable climaxes in the speech flow. 

Abry, C. (2003) [b ]-[d ]-[g ] as a universal triangle as
acoustically optimal as [i]-[a]-[u]. 15th Int. Congr. Phonetics
Sciences ICPhS, 727-730.

Schwartz, J.L., Boë, L.J., Vallée, N., Abry, C. (1997) The
Dispersion-Focalization Theory of vowel systems. J. Phonetics, 25,
255-286.

Butcher, A. (1994) On the phonetics of small vowel systems. SST-94, 1, 28-33.
Chomsky, N., Halle, M. (1968). The sound pattern of English. New York
: Harper & Row.

Fletcher, J., Butcher, A. (2003) Local and global infuences on vowel
formants in three Australian languages. 15th Int. Congr. Phonetics
Sciences ICPhS, 905-908

Jakobson, R., Fant, C.G.M., Halle, M. (1952). Preliminaries to speech
analysis. Cambridge: The MIT Press.

Lindblom B. (1986) Phonetic Universals in Vowel Systems. In J. Ohala
et al. Experimental Phonology, NY: Academic Press, 13-44.

MacNeilage,P.F., Davis, B. (2001) Motor mechanisms in speech
ontogeny: phylogenetic, neurobiological and linguistic implications.
Current Opinion in Neurobiology, 11, 696-700.