Study finds grammar drives dependency length minimization in 122 languages

A study analyzing 122 languages in Universal Dependencies and SUD version 2.17 reveals that dependency length minimization operates on two distinct levels rather than as a single uniform metric.

• Grammar-driven optimization targets functional dependencies (det, case, aux), which are universally short with a mean distance of 1.71 and low variance ($σ$ = 0.33).
• Processing-driven optimization affects lexical dependencies (nsubj, obj, obl), which are longer (mean 2.87), highly variable ($σ$ = 0.63), and constrained by word-order typology.
• This asymmetry persists in SUD despite reversed head direction, with a correlation of r = 0.92.

The authors conclude that grammar scaffolds sentences with local functional attachments, leaving processing pressures to determine the ordering of lexical heads.