West Slavic languages
Vowel length became distinctive (phonemic) in West and partially South Slavic. In the West Slavic languages it was accompanied by extensive contraction due to the loss of /j/, typically resulting in a long vowel. This process was centered in the Czech area, and covered Russian and Bulgarian areas at its extremes. This new length is preserved only in Czech and Slovak, but is lost in most other West Slavic varieties. Several West Slavic languages reflect older length contrasts in the form of new quality contrasts, indirectly preserving the distinction. For example, Polish "ó" and "ą" are reflexes of older long vowels, even though they are no longer long. Length was phonemicized in Serbo-Croatian and Slovene, depending on the pitch. In Neoshtokavian Serbo-Croatian no pre-tonic lengths are allowed; i.e. with Neoshtokavian retraction occurring the length of old long accented syllables was retained as a post-tonic length. In Slovene, length is restricted to the stressed position, with the exception of /ə/ which is always short.