However, unlike the high-vowel neutralization, this does not result in new homophones, as all voiced stops are prenasalized, meaning that the word kado ('corner') is pronounced [kaⁿdo].

In Standard Japanese, the palatal series was produced with palatalisation of alveolar consonants before the front vowel /i/ and the semivowel /j/; s → ɕ, t → tɕ, d → dʑ.

Archaeological findings, including corner-projected mound burials from 100–250 AD in the Noto Peninsula and Toyama Prefecture, provide evidence for early Izumo influence in these areas.

This implies that the distinctive vowel systems of Izumo likely spread to these regions during the Mid to Late Yayoi period.

[3] Elisabeth de Boer arguments in favour of an Izumo/Tōhoku branch within the Japanese dialects and that pre-existing trade contacts after the defeat of the Emishi in Tōhoku paved the way for immigration to the area.

Early Yayoi settlements in coastal areas such as Ishikawa, Toyama, and western Niigata date back to around 300 BC.

Migration into the Tōhoku region in the late 6th century matches archaeological evidence of the arrival of a new population similar to Kofun cultures found elsewhere in Japan.

The relatively low internal diversity of Tōhoku dialects can be attributed to the later spread of Japanese northeastward compared to other mainland regions of Japan.