Historical sound shifts, such as the diachronic diphthongization of Latin vowels under specific stress and environmental conditions, are well-documented drivers of stem-changing verbs in Spanish.
Papers [5] and [8] provide specific historical and linguistic evidence demonstrating that stem and vowel alterations in Spanish (such as diphthongization) arose from historical sound shifts tied to accentual structure and phonetic environments. The remaining papers discuss unrelated topics like neurological processing, iconicity, or vowel harmony in other language families, leaving the supporting evidence uncontested by any papers in the set.