While having a simple (though non-standard) definition, this function yields improved performance relative to the two suggested evaluation criteria -for vector quality and for word similarity.
the underlying idea is that a good characteristic feature for a word w should characterize also multiple words that are highly similar to w. such feature should have a substantial "focus" within the close semantic vicinity of w. Applying RFF weighting achieved about 10% improvement in predicting meaning entailing substitutability (Section 5).