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Miller, H. ., Friedrich, A. ., Narkavic, R. ., & Zentall, T. . (2009). A differential-outcomes effect using hedonically nondifferential outcomes with delayed matching to sample by pigeons. Learning & Behavior, 37(2), 161-6. https://doi.org/10.3758/LB.37.2.161 (Original work published 2009)