For almost 5 decades, the scientific study of emotion has been guided by the assumption that categories such as anger, sadness, and fear cut nature at its joints. Barrett (2006a) provided a comprehensive review of the empirical evidence from the study of emotion in humans and concluded that this assumption has outlived its usefulness. Panksepp and Izard have written lengthy papers (published in this issue) containing complementary but largely nonoverlapping criticisms of Barrett (2006a). In our response, we address three of their concerns. First, we discuss the value of correlational versus experimental studies for evaluating the natural-kind model of emotion and refute the claim that the evidence offered in Barrett (2006a) was merely correlational. Second, we take up the issue of whether or not there is evidence for "coherently organized neural circuits" for natural kinds of emotions in the mammalian brain and counter the claim that Barrett (2006a) ignored crucial evidence for existence of discrete emotions as natural kinds. Third, we address Panksepp and Izard's misconceptions of an alternative view, the conceptual act model of emotion, that was briefly discussed in Barrett (2006a). Finally, we end the article with some thoughts on how to move the scientific study of emotion beyond the debate over whether or not emotions are natural kinds."It would be very surprising indeed if the brain were organized into spatially discrete units that conform to our abstract categorizations of behavior." (Valenstein, 1973, pp. 142-143) According to the National Academy of Sciences in the United States, a theory is a wellsubstantiated explanation of a phenomenon. A theory is the end point of science-it is what scientists know to be true when observations have been confirmed by repeated experimentation (National Academy of Sciences, 1998). A hypothesis, on the other hand, is a tentative statement that must be tested. Barrett (2006a) demonstrated that after a century of empirical research, the natural-kind view of emotion is not yet a theory. It remains a set of hypotheses-or what we might call a model-subject to the same rules of scientific verification as any other model of emotion. It is a fact that people experience phenomena that are called (in English) anger, sadness, and fear. It is a fact that people experience these psychological states as discrete events that are bounded in time and that people often (but not always) experience these states as psychologically distinct from one another. It is also a fact that people easily and effortlessly see anger and sadness and fear in the behaviors of other people, including babies, and in nonhuman animals. People even see these emotions in the behaviors of shapes (squares, circles, and triangles) that move in a particular relation to one another (Heider & Simmel, 1944). It is the task of science to explain these facts: to explain how the events that people experience as anger, sadness, or fear are caused and how they are entailed in the brain. It is compelling to

Novel object and location recognition tasks harness the rat’s natural tendency to explore novelty (Berlyne, 1950) to study incidental learning. The present study examined the ontogenetic profile of these two tasks and retention of spatial learning between postnatal day (PD) 17 and 31. Experiment 1 showed that rats ages PD17, 21, and 26 recognize novel objects, but only PD21 and PD26 rats recognize a novel location of a familiar object. These results suggest that novel object recognition develops before PD17, while object location recognition emerges between PD17 and PD21. Experiment 2 studied the ontogenetic profile of object location memory retention in PD21, 26, and 31 rats. PD26 and PD31 rats retained the object location memory for both 10-min and 24-hr delays. PD21 rats failed to retain the object location memory for the 24-hr delay, suggesting differential development of short- versus long-term memory in the ontogeny of object location memory.

In the novel object recognition (OR) paradigm, rats are placed in an arena where they encounter two sample objects during a familiarization phase. A few minutes later, they are returned to the same arena and are presented with a familiar object and a novel object. The object location recognition (OL) variant involves the same familiarization procedure but during testing one of the familiar objects is placed in a novel location. Normal adult rats are able to perform both the OR and OL tasks, as indicated by enhanced exploration of the novel vs. the familiar test item. Rats with hippocampal lesions perform the OR but not OL task indicating a role of spatial memory in OL [1]. Recently, these tasks have been used to study the ontogeny of spatial memory but the literature has yielded conflicting results [2, 3]. The current experiments add to this literature by: 1) behaviorally characterizing these paradigms in postnatal day (PD) 21, 26 and 31-day-old rats; 2) examining the role of NMDA systems in OR vs. OL; and 3) investigating the effects of neonatal alcohol exposure on both tasks. Results indicate that normal-developing rats are able to perform OR and OL by PD21, with greater novelty exploration in the OR task at each age. Second, memory acquisition in the OL but not OR task requires NMDA receptor function in juvenile rats. Lastly, neonatal alcohol exposure does not disrupt performance in either task. Implications for the ontogeny of incidental spatial learning and its disruption by developmental alcohol exposure are discussed.

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