1. A device that provides a plurality of responses to a plurality of stimuli, wherein at least one preselected specific response is provided only when the operator of the device successfully matches a specific pair of said plurality of stimuli, and wherein said plurality of stimuli are divided into a first and second group of stimuli, said second group being subdivided into a plurality of sets of stimuli, the ordered arrangement of which differs as between different sets, so that a successful matching of a stimulus from said first group with a stimulus from a selected set of stimuli from said second group does not indicate to said operator how to make successive matches, wherein the improvement comprises, in combination, a first generating means for generating a first plurality of encoded signals, each of which first encoded signals represents a specific stimulus included in said first group of stimuli, a second generating means for generating a second plurality of encoded signals, each of which second encoded signals represents a specific stimulus included in said second group of stimuli, said first generating means being selectively operable to generate specific ones of said first plurality of encoded signals, said second generating means being selectively operable to generate specific ones of said second plurality of encoded signals, a memory means for storing all of the stimuli contained in said second group of stimuli, a selector means having as many positions as there are sets of stimuli in said second group of stimuli for re-calling from said memory means a specific set of stimuli from said second group of stimuli so that different sets of stimuli are re-called by each position of said selector means, a comparison means operatively connected to said second generating means, and to said memory means, said memory means adapted to transmit a first specific stimulus from a selected set of stimuli from said second group of stimuli to said comparison means responsive to selection by said operator of said first specific stimulus, said first generating means adapted to transmit a second specific stimulus from said first group of stimuli to said comparison means responsive to selection by said operator of said second specific stimulus, said comparison means providing a first response when said first specific stimulus matches said second specific stimulus, and providing a second response when said first specific stimulus does not match said second specific stimulus.