We present a method to implement novelty filtering and motion detection with two photorefractive crystals greatly different in response times as the two PCMs of a phase conjugate Michelson interferometer. Because this arrangement allows different combinations of crystals, the difference between the response times of the two arms can be very large and highly tunable, therefore the minimum detectable velocity of the moving object is significantly reduced and a strong and lasting image of the displaced object is obtained. We also report a method to equalize the phases and amplitudes of the phase conjugate waves from two crystals. Theoretical analysis of the relationship between the changing object and the output and experimental results are given.