The physiological, acoustic, and perceptual basis of high back vowel fronting: Evidence from German tense and lax vowels

High back rounded vowels are prone synchronically to fronting in a fronting context and diachronically they are more likely to front than high front vowels are to retract. In order to shed light on the reasons for this back–front asymmetry, tense and lax vowels produced in three place of articulation contexts by seven first-language speakers of German at two speech rates were analysed physiologically, acoustically, and perceptually. An articulographic analysis showed greater magnitudes and peak velocities of horizontal tongue dorsum movement in CV transitions for /u:, o:/ than for /e:, i:/. A second experiment showed that the difference between tense and lax vowels in the tongue dorsum's horizontal position was greater for back than front vowels. A third experiment showed /u:, ʊ/ were more likely to encroach on the /y:, ʏ/ spaces than the other way round for measurements based both on the horizontal tongue dorsum position and on spectral slope; a similar pattern of results emerged in a forced-choice perception experiment. The general conclusion is that high back vowels that are as peripheral as those in German have a high articulatory cost which may explain both the diachronic tendency for back vowels to front and why the absence of a high back vowel often contributes to asymmetric vowel distributions in the world's languages.