Brown University has their portrait collection online! And so finding out about the painting was relatively easy.
From the bio on Brown's online portrait collection, it is clear Walter Samuel Hunter (1889-1954) was a much beloved professor of Psychology from 1936-1954.
Brown did not post a color photo -- and very sadly this painting appears to have been stolen in 2009! (They used the words, "disappeared" and "unlocated". Wonder why? Could it have happened during a remodel or something? Or do they think it was stolen?)
More info on the painting and the man can be found here:
Update September 17, 2015: according to this source, my grandfather was a friend and painting tutor to Dr. Hunt! (Brown Alumni monthly December 1958: http://archive.org/stream/brownalumnimonth593brow/brownalumnimonth593brow_djvu.txt