This is a brief sampler of European and Wajin Japanese statements on the mental and temperamental characteristics of the Ainu (for the most part, 19th- and early 20th-century Hokkaido Ainu). I’m not in any position to vouch for the accuracy or generalizability of any of the informal accounts, nor for the methodological soundness of the psychometric tests described in the last excerpt, but hopefully this post conveys both the extremes of opinion and a few points of consensus. All emphasis mine.
William Elliot Griffis, writing in The Japanese nation in evolution (1907):
… In the working of their minds, in apprehension of our ways and thoughts and needs of daily life (though not in abstract science), as American and British travellers in our day and generation tell us, they are decidedly Aryan, more so than the smarter Japanese. Mr. Archibald Gowan Campbell, in 1898, besides remarking on their fine physique, says of the Ainu, “they have a distinct bias for veracity and will frequently tell the truth to their own disadvantage,” and that both sexes are devoid of the insatiable curiosity of the Japanese; that many Ainu are distinctly handsome, and the children are singularly European in their ways, that the Ainu intelligence is limited, but it seems to be of the same kind as our own and not of the Asiatic order; that an Ainu readily understands European signs, while a Japanese invariably gets them upside down; that it is easier to make a novel request to an Ainu than to a Japanese, owing to the simplicity of the one and the conventionality of the other.