In itself, such extrapolation is hardly fatal. Freud built his account of human behavior from his work on patients in Vienna and generalized for the world. So many great analysts of human nature, from Aristotle to the Buddha, reached for transcendent human truths despite limited contact with the range of humanity.

The Canadian study’s claim is not to invalidate all extrapolation so much as to suggest that American undergraduates may be especially unsuitable for it.

The study’s method was to analyze a mountain of published, peer-reviewed psychology papers. It found evidence both of a narrow research base and of the eccentricity of that base. Among the many peculiarities of the usual subjects who serve as “universal man” are these, the study found:

American subjects disproportionately prize choice and individualism. In a survey of six Western societies, only Americans preferred a choice of 50 ice creams to 10. Studies have found that Americans are all but alone in giving newborns their own room.

Americans are also peculiar in the so-called Ultimatum Game, in which a subject receives money and must make an offer to share it. The second subject can accept or reject the offer, but if it is rejected, neither subject gets paid.

Americans playing the game are fair in the extreme, making higher offers than most. But they are also outliers in another way. In various places, including Russia and China, psychologists observe the rejection of excessive generosity — a demurring when offered too much. This behavior is absent from American undergraduates.

The study’s list goes on and on. Westerners tend to define themselves by psychological traits, and non-Westerners by relationships. In some languages, including English, directions are built around the self (“Take a right after the church”), while in other languages, they refer to immovable objects (“It is behind the church”).

Americans are worse than many at overcoming common optical illusions about the length of lines. But they are better than East Asians at recalling an object when the background changes, perhaps because the latter focus on context.