Abstract: Three experiments were conducted to test whether a pair of tufted capuchin monkeys (Cebus apella) could generalize their ability to exchange tokens and tool objects with a human experimenter to similar exchanges with a conspecific partner. Monkeys were tested in side-by-side enclosures, one enclosure containing a tool-use apparatus and one or more token(s), and the other enclosure containing one or more tool object(s). The monkeys willingly transferred tokens and tools to a conspecific with little practice. Following a small amount of training, we also found that the monkeys would select situation-appropriate tokens to exchange for specific tools, but did not select appropriate tool objects in response to another monkey's token transfers. Implications regarding role reversal are discussed.

Abstract: This work evaluated the prospect that organizational accounts of the retention of list information by monkeys might be an artifact of familiarity with conditional relationships. Seven sophisticated macaques were trained on four five-item lists. Each acquisition selectively excluded one of the internal conditional pairs of the typical four-problem sequence (AB,BC,CD,DE) that defines a five-item serially ordered list. Then, all possible novel pairings and the trained pairs appeared together in a test. After this, the previously omitted pair was trained and animals were retested. On all tasks, initial tests revealed little organization and much intersubject variability of characteristic choice strategies, but subsequent inclusion of all four conditional pairs always yielded organized serial choice. On both the four-problem tests and in a later retention, errors were directly related to interitem distance between the objects paired on test trials. These results helped to specify the conditions required for demonstration of non-human primate analogs of transitivity, and showed that even sophisticated monkeys organize information in retention only if they know all interitem relationships.

Abstract: This study was aimed at uncovering physical and geometric properties that make a particular landmark a target of exploration and navigation. Rats were tested in a square open-field arena with additional portable corners featuring the same properties as the arena corners. It was found that the routes of progression converged upon the added corners, whether located at the arena wall or the arena center. Route convergence upon the added corners involved numerous visits to these corners. However, time spent at the added corners was relatively short compared with the arena corners, including that from which rats were introduced into the arena. There was no differential effect of testing rats in light or dark, or with a low versus a high portable corner. It is suggested that the added corners were distinct against the background of the arena enclosure, whereas the four arena corners and walls were encoded by the rats as one geometric module. This distinctness, together with the greater accessibility of the added corners, made them salient landmarks and a target of exploration. Thus, the impact of a landmark extended beyond its specific self-geometry to include accessibility and distinctness, which are contextual properties. In addition to the contextual impact on locomotor behavior there was also a temporal effect, with security initially dominating the rats' behavior but then declining along with an increased attraction to salient landmarks. These spatiotemporal patterns characterized behavior in both lit and dark arenas, indicating that distal cues were secondary to local proximal cues in shaping routes.

Abstract: This study tests whether the face-processing system of humans and a nonhuman primate species share characteristics that would allow for early and quick processing of socially salient stimuli: a sensitivity toward conspecific faces, a sensitivity toward highly practiced face stimuli, and an ability to generalize changes in the face that do not suggest a new identity, such as a face differently oriented. The look rates by adult tamarins and humans toward conspecific and other primate faces were examined to determine if these characteristics are shared. A visual paired comparison (VPC) task presented subjects with either a human face, chimpanzee face, tamarin face, or an object as a sample, and then a pair containing the previous stimulus and a novel stimulus was presented. The stimuli were either presented all in an upright orientation, or all in an inverted orientation. The novel stimulus in the pair was either an orientation change of the same face/object or a new example of the same type of face/object, and the stimuli were shown either in an upright orientation or in an inverted orientation. Preference to novelty scores revealed that humans attended most to novel individual human faces, and this effect decreased significantly if the stimuli were inverted. Tamarins showed preferential looking toward novel orientations of previously seen tamarin faces in the upright orientation, but not in an inverted orientation. Similarly, their preference to look longer at novel tamarin and human faces within the pair was reduced significantly with inverted stimuli. The results confirmed prior findings in humans that novel human faces generate more attention in the upright than in the inverted orientation. The monkeys also attended more to faces of conspecifics, but showed an inversion effect to orientation change in tamarin faces and to identity changes in tamarin and human faces. The results indicate configural processing restricted to particular kinds of primate faces by a New World monkey species, with configural processing influenced by life experience (human faces and tamarin faces) and specialized to process orientation changes specific to conspecific faces.

Abstract: This study investigated whether dolphins would show evidence of equivalence class formation between auditory stimuli. Bottlenose dolphins were trained to press one or other of two response levers depending on which one of four auditory stimuli had been previously presented. Once they had learned the initial discriminations, the stimulus-lever contingencies was repeatedly reversed. Within any given session, however, pressing of one lever always led to reward with one set of two tones and pressing the other lever led to non-reward with an alternative set of two tones. After sufficient experience with this response reversal procedure, the dolphins spontaneously chose the same levers they had first learned to be correct with one of the across-set stimulus pairs when later in the session they were presented with the other of the across-set stimulus pairs. They thus demonstrated that they had associated the tones belonging to the two sets within two separate functional classes. It is discussed why the dolphins succeeded with auditory stimuli when they had previously failed in a similar task with visual stimuli.