How are Four-Level Length Distinctions Produced? Evidence from Moroccan Arabic

We investigate the durational properties of Moroccan Arabic identical consonant sequences contrasting singleton (S) and geminate (G) dental fricatives, in six combinations of four-level length contrasts across word boundaries (#) (one timing slot for #S, two for #G and S#S, three for S#G and G#S, and four for G#G). The aim is to determine the nature of the mapping between discrete phonological timing units and phonetic durations. Acoustic results show that the largest and most systematic jump in duration is displayed between the singleton fricative on the one hand and the other sequences on the other hand. Looking at these sequences, S#S is shown to have the same duration as #G. When a geminate is within the sequence, a temporal reorganization is observed: G#S is not significantly longer than S#S and #G; and G#G is only slightly longer than S#G. Instead of a four-way hierarchy, our data point towards a possible upper limit of three-way length contrasts for consonants: S < G=S#S=G#S < S#G=G#G. The interplay of a number of factors resulting in this mismatch between phonological length and phonetic duration are discussed, and a working hypothesis is provided for why duration contrasts are rarely ternary, and almost never quaternary.