In East Slavic, akan'e (neutralization of /o/ and /a/ after non-palatalized consonants) has spread or is spreading to dialects which maintain the mid- and low-vowel contrast (okan'e). Under the assumption that vowel neutralization is favored in durationally deprived syllables, it is expected that akan'e would first spread in weak positions, and in some transitional dialects this is exactly what happens: akan'e is found in non-immediately pretonic and post-tonic syllables. But in other dialects the patterns of akan'e spread are unexpected: it first appears in the immediately pretonic position and before stressed high vowels and often before stressed /a/ before it occurs elsewhere. I focus on these unexpected patterns and suggest that they may emerge as a consequence of perceptual salience through contact with neighboring strong akan'e dialects in Pskov and Novgorod oblasts of Russia and in Homel' and Minsk oblasts of Belarus. Similar patterns are found in other East Slavic dialect contact situations under similar conditions, as is to be expected.