In 1988 Tjeerd de Graaf was invited by the for a stay of three month at Hokkaido University in Sapporo. Since then he joined various project groups, such as the first international expedition in 1990 to the island of Sakhalin, where the language and culture of the local minority peoples (in particular Nivkh) were studied . In 1988 Tjeerd de Graaf was invited by the Japanese Society for the Promotion of Science for a stay of three month at Hokkaido University in Sapporo. Since then he joined various project groups, such as the first international expedition in 1990 to the island of Sakhalin, where the language and culture of the local minority peoples (in particular Nivkh) were studied .

In the following years he spent several longer periods at Japanese institutions, such as Chiba University (2000) and the Slavic Research Institute of Hokkaido University (2004,2005). He did fieldwork on Sakhalin together with his research student Hidetoshi Shiraishi, who finished a dissertation on Topics in Nivkh Phonology at Groningen University in September 2006. 

References

More details can be found in the following reports: 

• Dissertation project of Hidetoshi Shiraishi 2002-2006
• Japan Foundation Fellowship Final Report 2000
• Minority Languages and Cultures in Japan, Europe and Russia
• Research report in Japan  2004
• Slavic Research Center of Hokkaido University
• Research report in Japan, September-November 2005
• Slavic Research Center of Hokkaido University
• Development of a Frisian and Dutch grammar for Japanese students