Mirror reversal simply explained without recourse to psychological processes.

This paper proposes a simple and definitive solution to the mirror reversal problem, "Why does a mirror reverse left and right but not up and down?" The solution is given by combining the inversion caused by the optical process of mirroring and the definition of the left-right axis. Thus the left-right reversal of mirror images essentially does not involve psychological processes, in contrast to the multiprocess hypothesis recently proposed by Takano.