Complex sentence: In 1987, he moved to the University of Michigan, where he was professor of psychology for four years, during the latter two of which he simultaneously held the position of research scientist at Michigan's Institute for Social Research.
Split into simpler sentences: In 1987, he moved to the University of Michigan, where he was professor of psychology for four years. During the last two years, he simultaneously held the position of research scientist at Michigan's Institute for Social Research.