Alhazen and the nearest neighbor rule

•We show that the NN rule can be found in a medieval vision treatise by Alhazen.•We provide a brief description of the salient points of Alhazen’s theory.•We argue that Alhazen’s is the first explicit formulation of the NN rule on record.

We show that a clear formulation of the nearest neighbor decision rule for pattern classification can be found, along with other remarkably modern ideas, in an influential medieval treatise on visual perception authored by Alhazen, one of the major figures in the so-called “Islamic golden age.” To put the work in context we provide also a brief description of some of the salient points of Alhazen’s theory.