How do Lithuanian and Latvian differ in their vowel changes?

Lithuanian and Latvian exhibit significant differences in their vowel systems, primarily because Lithuanian has remained more archaic, while Latvian has undergone several phonological shifts.1

Key vowel changes and differences include:

• Sound Combinations: Lithuanian has faithfully preserved the old sound combinations an, en, in, and un. In Latvian, these have consistently shifted to uo, ie, ī, and ū (e.g., Lithuanian rankà corresponds to Latvian roka).1
• Diphthongs: In Latvian, the diphthongs ei (and ai) and au in final positions were monophthongized and subsequently shortened.1
• Vowel Length and Loss: Latvian has shortened long vowels at the end of polysyllabic words and dropped short vowels entirely. For example, the Lithuanian sāko corresponds to the Latvian saka, and the Lithuanian pelė corresponds to the Latvian pele.1
• Intonation: While Lithuanian maintains a free stress, Latvian features a fixed stress on the first syllable. Latvian is considered more archaic regarding Proto-Baltic intonations; it preserved the falling character of the circumflex intonation (which became rising in Lithuanian) and retained the rising character of the acute intonation (which became falling in Lithuanian).1