A rat lever designed to minimize partial presses

The force required to move commercial spring-loaded rat levers increases with lever displacement. This, characteristic allows the rat to terminate barpresses before they are recorded. Such partial presses are unlikely to occur when the force requirement rapidly decreases as displacement increases. This inverse relationship between force and displacement can be achieved by requiring the rat to lift the tail of the bar out of a magnetic field; the consequence is that the bar “falls out from under” the S, and nearly all movements of the bar result in switch closure. The use of electromagnetic fields provides two additional advantages: the force requirement can be established and monitored remotely.