Recognition performance does not usually change along the lifespan, but the response criterion usually does, and in general, it changes from being conservative during youth to being liberal, in old age. The focus of the present study is to analyze the changes that take place, both in discrimination and response criterion, as a result of aging in two recognition tasks: one with neutral images, and the other with faces showing positive and negative emotional expressions. Two groups of participants performed both tasks: young (N = 21; age range, 17-33 years), older (N = 21; age range, 65-91 years). The analyses of several discrimination parameters (d' and probability of recognition) and the response criterion yielded significant age differences. Thus, results indicated that the ability to discriminate of older participants was better than that of younger participants when having to recognize neutral images, and faces with negative emotional expressions. The response criterion of younger participants was always conservative, whereas older participants only showed liberal criteria in front of faces with emotional expressions. In relation to the neutral images, the response criterion of older participants was optimum, because it led to more hits, without increasing the false alarms. The results are partially explained by the tasks differential difficulty, and are discussed within the frame of Simulation theory.