Pigeons were trained with 4 pairs of visual stimuli in a 5-term series-A+ B-, B+ C-, C+ D-. and D+ E-(in which plus[+] denotes reward and minus(-] denotes nonreward)-before the unreinforced test pair B D was presented. All pigeons chose Item 8, demonstrating inferential choice. A novel theory (value transfer theory), based on reinforcement mechanisms, is proposed. In Experiment 2, the series was extended to 7 terms. Performance on test pairs was transitive, and performance on training pairs accorded with the theory. The 7-term series was closed in Experiment 3 by training the flrst and last items together. In accordance with the theory, the Ss could not solve the circular series. The authors suggest that primates, including humans, also solve these problems using the value transfer mechanism, without resorting to the symbolic processes usually assumed. 1. Edith is fairer than Suzanne. 2. Edith is darker than Lili. 3. Who is the darkest, Edith, Suzanne, or Lili? Here the competent subject concludes that Suzanne is the darkest, although no direct information about the relationship between Lili and Suzanne was given. In this purely linguistic Juan D. Delius and Lorenzo von Fe~n were supported by the Deutsche Forschungsgemeinschaft, Bonn; C. D. L. Wynne was SUJ>ported by the Science and Engineering Research Council, London, and the Alexander von Humboldt.Stiftung, Bonn; and J. E. R. Staddon was supported by the National Science Foundation and the Alexander von Humboldt-Stiftung. We thank W. Mathaus for initial motivation, F. von Mi.inchow-Pohl for assistance in programming, and A. Lohmann for help in running the experiments. We are grateful to A. Elepfandt, B. Mc-Gonigle, J. Pearce, H. Terrace, and T. Trabasso for helpful comments on drafts of this article.

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Over the last two decades increasing evidence for an acute sensitivity to human gestures and attentional states in domestic dogs has led to a burgeoning of research into the social cognition of this highly familiar yet previously under-studied animal. Dogs (Canis lupus familiaris) have been shown to be more successful than their closest relative (and wild progenitor) the wolf, and than man's closest relative, the chimpanzee, on tests of sensitivity to human social cues, such as following points to a container holding hidden food. The "Domestication Hypothesis" asserts that during domestication dogs evolved an inherent sensitivity to human gestures that their non-domesticated counterparts do not share. According to this view, sensitivity to human cues is present in dogs at an early age and shows little evidence of acquisition during ontogeny. A closer look at the findings of research on canine domestication, socialization, and conditioning, brings the assumptions of this hypothesis into question. We propose the Two Stage Hypothesis, according to which the sensitivity of an individual animal to human actions depends on acceptance of humans as social companions, and conditioning to follow human limbs. This offers a more parsimonious explanation for the domestic dog's sensitivity to human gestures, without requiring the use of additional mechanisms. We outline how tests of this new hypothesis open directions for future study that offer promise of a deeper understanding of mankind's oldest companion.

We hypothesize that selection during dog domestication targeted CNVs associated with hypersociability.

We review studies claiming that fish feel pain and find deficiencies in the methods used for pain identification, particularly for distinguishing unconscious detection of injurious stimuli (nociception) from conscious pain. Results were also frequently misinterpreted and not replicable, so claims that fish feel pain remain unsubstantiated. Comparable problems exist in studies of invertebrates. In contrast, an extensive literature involving surgeries with fishes shows normal feeding and activity immediately or soon after surgery. C fiber nociceptors, the most prevalent type in mammals and responsible for excruciating pain in humans, are rare in teleosts and absent in elasmobranchs studied to date. A‐delta nociceptors, not yet found in elasmobranchs, but relatively common in teleosts, likely serve rapid, less noxious injury signaling, triggering escape and avoidance responses. Clearly, fishes have survived well without the full range of nociception typical of humans or other mammals, a circumstance according well with the absence of the specialized cortical regions necessary for pain in humans. We evaluate recent claims for consciousness in fishes, but find these claims lack adequate supporting evidence, neurological feasibility, or the likelihood that consciousness would be adaptive. Even if fishes were conscious, it is unwarranted to assume that they possess a human‐like capacity for pain. Overall, the behavioral and neurobiological evidence reviewed shows fish responses to nociceptive stimuli are limited and fishes are unlikely to experience pain.

Transitive inference is the ability, given that A >B andB > C, to infer that A > C. Pigeons, rats, chimpanzees, squirrel monkeys, and humans as young as 4 years have all been shown capable of this. In this paper, simple associative learning models are explored as accounts of nonverbal transitive inference performance. A Bush-Mosteller-based model can account for transitive inference under limited conditions. A Rescorla-Wagner-based model can account for transitive inference under all conditions in the literature, but cannot account for some additional nontransitive tests. Afinal configural model can also account for these nontransitive data. The ability of this model to account for transitive inference formation in humans is also considered.The transitive inference task is a form of syllogism familiar to the ancient Greeks and introduced into psychology by Cyril Burt (1911; 1919a, 1919b. Of Burt's tests for assessing the reasoning powers of 7-year-old children, two of the three he considered best for a short test were of the following form:Tom runs faster than Jim: Jack runs slower than Jim. Who is the slowest-Jim, Jack, or Tom? (Burt, 1919a, p. 73) Burt maintained an interest in this task because it correlated well with other measures of intelligence. Piaget was interested in Burt's syllogisms for the light that they could shed on the development of basic intellectual faculties (Piaget, 1928). For Piaget, success on transitive inference syllogisms is part of a general ability to seriate stimuli, as well as evidence for the concrete operational stage of intellectual development (Flavell, 1963).The ability to seriate sets of stimuli, given only partial information about the relationships between them, has far wider generality than does the simple completion of syllogisms. For social animals to be able to estimate their rank in relation to many conspecifics without entering potentially dangerous interactions with every other member of the group must often be adaptive (Cheney & Seyfarth, 1986). Similarly, the ranking offood-item prefThis research was supported by a grant to the author from the Department of Psychology, University of Western Australia, and by grants to John Staddon from the NSF and NIMH. I am grateful to Janice Steirn and Tom Zentall for making data available prior to publication and to Howard Eichenbaum, Tom Zentall, Yin LoLordo, and two anonymous reviewers for helpful comments on earlier drafts. Address correspondence to C. D. L. Wynne, Department of Psychology, University of Westem Australia, Nedlands, Perth, WA 6009, Australia (e-mail: c1ive@psy.uwa.edu.au). Wynne, 1994 [pigeons D. Given that verbal reasoning still seems outside the reach of all except the human species, we may therefore predict that the mechanisms underlying these kinds of performances can be much simpler than hitherto assumed. This paper demonstrates how a complex cognitive ability can be the result of familiar associative mechanisms. This argument will be developed with the use of data from pigeon subjects, but the logic a...

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