I think the notion of a drop off due to culture shock is reasonable, but overblown. As a hockey fan, this was given the ultimate test when the Soviet Union fell. Players who defected to the NHL (Pavel Bure, Alexander Mogilny, Sergei Federov, Viacheslav Fetisov, Sergei Makarov, etc.) were immediately stars in the NHL. For those unfamiliar with the strength of Soviet hockey, most people believe CSKA Moscow would have been a strong NHL team. Looking back, it seemed that the NHL needed to adjust to the agility and finesse of these players as much as these players had to adjust to the toughness of hockey across the pond. Makarov is a great player to compare to the Japanese baseball players: he came over at age 32, won the Calder Trophy (rookie of the year), and saw his production steadily decline from age 33 - 36. I know baseball is a different sport, and going from the Soviet Union to North America is different than going from Japan to the U.S., but I still believe this to be strong evidence that athletes do not struggle as much with culture shock as it is often said. The transition from the Japanese game to the U.S. game for pitchers is somewhat similar to the transition from the Soviet game to the North American game: Compared to the Japanese pitchers, North Americans rely much more on power, while the Japanese pitchers typically rely on craftiness, just like the Soviet hockey players relied on finesse, craftiness, and agility rather than the brute force of the Canadians. I'll reiterate that baseball is a far different sport from hockey, but I see little reason to believe that if the two leagues were even close to equally matched, there would be little more than the typical drop in production that comes at that age (see: Makarov, Sergei). As I noted, the difference in playing style should not always hurt the Japanese players, as the MLB'ers must also adjust to their game.