By the end of the thirteenth century several models of visual perception were available in the Latin West, differing according to their influences – Aristotelian, Augustinian, Avicennian – and their interpretations. One such model was that of perspectivist optics, as espoused by Alhacen and popularized by Roger Bacon. While the general structure of this theory is well-known, until recently scholars have paid less attention to the issue of discrimination – distinction, comparison, judgment – by a higher cognitive faculty (the virtus distinctiva) of incoming sensory information. In my paper, I specifically examine what role this discriminative faculty, as proposed by Alhacen, plays in the works of later perspectivi such as Roger Bacon, John Pecham, and Blasius of Parma, proceeding from the assumption that the best way to understanding the influence of any given theory is by understanding the authors influenced by it. My focus is on two aspects of this power: what exactly its functions are, and whether its nature is rational or sensory. Building on this last aspect, I consider whether this nature is better suited for passive or active accounts of perception.