POLYPROPYLENE PELLETS AS AN INEXPENSIVE REUSABLE SUBSTITUTE FOR MILK IN THE MORRIS MILK MAZE

A new inexpensive opaquing agent for the Morris milk maze is described . Small light-weight polypropylene pellets that float on the surface o f the water were used to eliminate visual cues about the location of t he hidden platform without impeding swimming or the use of distal spat ial cues. Results obtained using the pellets are identical to those ob tained with milk powder as an opaquing agent. An automatic tracking sy stem works as well with the pellet as with the milk version of the maz e.