Imagine you are a scientist seeking to determine the effects of age and amount of exposure to stimuli on infants' memory durability. Identify the independent variables in this hypothetical experiment and propose experimental manipulations that would allow you to test the hypothesis that older infants require less exposure than young infants, but their memories are nevertheless more durable. Design a version of this experiment using 

(1) the visual comparison paradigm; 

(2) The conjugate reinforcement paradigm and 

(3) the imitation paradigm.