CV coarticulation, locus and locus equation perspective on the invariance issue involving Algerian Arabic consonants

• Six locus equations for Algerian Arabic consonants are generated.
• The variability of F2F3 at the onset increases as the F2 transition extent increases.
• A more accurate method for the degree of coarticulation is presented.
• Variability of [b] and [ɡ] loci is explained.
• 98% correct classification for place separation is obtained.

The aim of the present investigation is to strengthen the link between coarticulation and locus theory of speech perception through the analysis and discrimination of six Algerian Arabic consonants [b], [d], [ɡ], [q], [ʕ], [h] representing respectively six places of articulation: labial, alveolar, velar, uvular, pharyngeal, laryngeal. When plotting the error area of the categories formed by (F2onset, F3onset) samples within a CV syllable across all speakers against the F2 transition extent mean(abs(F2onset–F2vowel)), a linear correlation is observed. Then a formula for the degree of coarticulation is derived from this straight line and it is shown that it is more reliable than the slope of the locus line. When combined with the locus equation's linearity, another equation is obtained and appears to be well fitted with locus theory. Another observation in our data concerns the deviation of syllables with respect to the locus line, as in the previously noted case of [ɡ] with back vowels. Moreover, it is shown that these shifts are speaker dependent and a consequence of interactions between the categories cited above. Finally, it is shown how better place separation is obtained when these categories are mapped in the auditor's perception space using the modified locus equation.