1. A method for preventing user preference for any of two or more training processes, each of which, when executed, presents stimuli to the user wherein the stimuli is designed primarily to improve a cognitive ability of the user and measures the cognitive ability of the user by comparison of responses of the user to the stimuli to predetermined correct responses, the method comprising: establishing a token economy in which points are awarded during play of each of the training processes by a user as a token currency; for each of the training processes: determining an amount of effort required by the user to correctly respond to stimuli of the training process relative to respective amounts of effort required to correctly respond to stimuli of others of the training processes; and establishing a number of points to be awarded to the user for correctly responding to the stimuli, wherein the number of points is directly related to the amount of effort required by the user to correctly respond to the stimuli.