The dolphin's (Tursiops truncatus) understanding of human gazing and pointing: Knowing what and where.

The authors tested whether the understanding by dolphins (Tursiops truncatus) of human pointing and head-gazing cues extends to knowing the identity of an indicated object as well as its location. In Experiment 1, the dolphins Phoenix and Akeakamai processed the identity of a cued object (of 2 that were present), as shown by their success in selecting a matching object from among 2 alternatives remotely located. Phoenix was errorless on first trials in this task. In Experiment 2, Phoenix reliably responded to a cued object in alternate ways, either by matching it or by acting directly on it, with each type of response signaled by a distinct gestural command given after the indicative cue. She never confused matching and acting. In Experiment 3, Akeakamai was able to process the geometry of pointing cues (but not head-gazing cues), as revealed by her errorless responses to either a proximal or distal object simultaneously present, when each object was indicated only by the angle at which the informant pointed. The overall results establish that these dolphins could identify, through indicative cues alone, what a human is attending to as well as where. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Seeing through sound: Dolphins (Tursiops truncatus) perceive the spatial structure of objects through echolocation.

Experiment 1 tested a dolphin (Tursiops truncatus) for cross-modal recognition of 25 unique pairings of 8 familiar, complexly shaped objects, using the senses of echolocation and vision. Cross-modal recognition was errorless or nearly so for 24 of the 25 pairings under both visual to echoic matching (V-E) and echoic to visual matching (E-V). First-trial recognition occurred for 20 pairings under V-E and for 24 under E-V. Echoic decision time under V-E averaged only 1.88 s. Experiment 2 tested 4 new pairs of objects for 24 trials of V-E and 24 trials of E-V without any prior exposure of these objects. Two pairs yielded performance significantly above chance in both V-E and E-V. Also, the dolphin matched correctly on 7 of 8 1st trials with these pairs. The results support a capacity for direct echoic perception of object shape by this species and demonstrate that prior object exposure is not required for spontaneous cross-modal recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comprehension of signs by dolphins (Tursiops truncatus).

The authors assessed the ability of 6 captive dolphins (Tursiops truncatus) to comprehend without explicit training 3 human communicative signs (pointing, directed gaze, and replica). Pointing consisted of indicating the target item with the index finger and a fully extended arm. Directed gaze consisted of orienting the head and eyes toward the target item while the rest of the body remained stationary. The replica signal consisted of holding up an exact duplicate of the target item. On the initial series of 12 trials for each condition, 3 dolphins performed above chance on pointing, 2 on gaze, and none for replica. With additional trials, above chance performance increased to 4 dolphins for pointing, 6 for gazing, and 2 for replica. The replica sign seemed to be the most taxing for them (only 2 dolphins achieved results significantly above chance). Taken together, these results indicate that dolphins are able to interpret untrained communicative signs successfully. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Matching-to-sample by an echolocating dolphin (Tursiops truncatus).

An adult male dolphin was trained to perform a three-alternative delayed matching-to-sample task while wearing eyecups to occlude its vision. Sample and comparison stimuli consisted of a small and a large plastic tube, a water-filled stainless steel sphere, and a solid aluminum cone. Stimuli were presented under water and the dolphin was allowed to identify the stimuli through echolocation. The echolocation clicks emitted by the dolphin to each sample and each comparison stimulus were recorded and analyzed. Over 48 sessions of testing, choice accuracy averaged 94.5% correct. This high level of accuracy was apparently achieved by varying the number of echolocation clicks emitted to various stimuli. Performance appeared to reflect a pre-experimental stereotyped search pattern that dictated the order in which comparison items were examined and a complex sequential-sampling decision process. A model for the dolphin's decision-making processes is described. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discriminative responding of a dolphin (Tursiops truncatus) to differentially rewarded stimuli.

Examined the ability of 2 female Atlantic bottle-nosed dolphins to maximize reward in a discrimination learning task with multiple differentially rewarded stimuli. Although both dolphins reportedly performed well, results refer primarily to only 1 S. Results show that the S learned to choose, from among simultaneous groupings of 2–5 objects, the object that represented the greatest food value. The S surpassed the accomplishments of other animals previously tested by responding appropriately to all groupings of 6 different representational objects, each associated with a different food value, even after an 11-wk separation from the objects. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Atlantic bottlenose dolphin (Tursiops truncatus) hearing threshold for brief broadband signals.

The hearing sensitivity of an Atlantic bottlenose dolphin (Tursiops truncatus) to both pure tones and broadband signals simulating echoes from a 7.62-cm water-filled sphere was measured. Pure tones with frequencies between 40 and 140 kHz in increments of 20 kHz were measured along with broadband thresholds using a stimulus with a center frequency of 97.3 kHz and 88.2 kHz. The pure-tone thresholds were compared with the broadband thresholds by converting the pure-tone threshold intensity to energy flux density. The results indicated that dolphins can detect broadband signals slightly better than a pure-tone signal. The broadband results suggest that an echolocating bottlenose dolphin should be able to detect a 7.62-cm diameter water-filled sphere out to a range of 178 m in a quiet environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bubble ring play of bottlenose dolphins (Tursiops truncatus): Implications for cognition.

Research on the cognitive capacities of dolphins and other cetaceans (whales and porpoises) has importance for the study of comparative cognition, particularly with other large-brained social mammals, such as primates. One of the areas in which cetaceans can be compared with primates is that of object manipulation and physical causality, for which there is an abundant body of literature in primates. The authors supplemented qualitative observations with statistical methods to examine playful bouts of underwater bubble ring production and manipulation in 4 juvenile male captive bottlenose dolphins (Tursiops truncatus). The results are consistent with the hypothesis that dolphins monitor the quality of their bubble rings and anticipate their actions during bubble ring play. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The uncertain response in the bottlenosed dolphin (Tursiops truncatus).

Humans respond adaptively to uncertainty by escaping or seeking additional information. To foster a comparative study of uncertainty processes, we asked whether humans and a bottlenosed dolphin (Tursiops truncatus) would use similarly a psychophysical uncertain response. Human observers and the dolphin were given 2 primary discrimination responses and a way to escape chosen trials into easier ones. Humans escaped sparingly from the most difficult trials near threshold that left them demonstrably uncertain of the stimulus. The dolphin performed nearly identically. The behavior of both species is considered from the perspectives of signal detection theory and optimality theory, and its appropriate interpretation is discussed. Human and dolphin uncertain responses seem to be interesting cognitive analogs and may depend on cognitive or controlled decisional mechanisms. The capacity to monitor ongoing cognition, and use uncertainty appropriately, would be a valuable adaptation for animal minds. This recommends uncertainty processes as an important but neglected area for future comparative research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Whistle contour development in captive-born infant bottlenose dolphins (Tursiops truncatus): Role of learning.

Whistles from captive-born infant bottlenose dolphins (Tursiops truncatus) were recorded during normal social interactions from birth over the 1st year of development and analyzed for acoustic structure, use, and context. Results indicate that 2 predominant whistle types were shared by all the infants across all social groups. The remainder of the whistle repertoire was composed of signals that were shared by several infants or across infant and adults and those that were individually unique. Ontogenetic changes were found in the structure, use, and contextual usage of whistle types in infants. Evidence for vocal plasticity and learning was found in the acoustic composition of infant whistle repertoires and in the use of whistle types. Results parallel those reported for the early stages of vocal learning in humans and songbirds, suggesting possible convergent strategies for vocal development and learning across divergent animal groups. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Whistle rates of wild bottlenose dolphins (Tursiops truncatus): Influences of group size and behavior.

In large social groups acoustic communication signals are prone to signal masking by conspecific sounds. Bottlenose dolphins (Tursiops truncatus) use highly distinctive signature whistles that counter masking effects. However, they can be found in very large groups where masking by conspecific sounds may become unavoidable. In this study we used passive acoustic localization to investigate how whistle rates of wild bottlenose dolphins change in relation to group size and behavioral context. We found that individual whistle rates decreased when group sizes got larger. Dolphins displayed higher whistle rates in contexts when group members were more dispersed as in socializing and in nonpolarized movement than during coordinated surface travel. Using acoustic localization showed that many whistles were produced by groups nearby and not by our focal group. Thus, previous studies based on single hydrophone recordings may have been overestimating whistle rates. Our results show that although bottlenose dolphins whistle more in social situations they also decrease vocal output in large groups where the potential for signal masking by other dolphin whistles increases. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Coordinated breathing in bottlenose dolphins (Tursiops truncatus) as cooperation: Integrating proximate and ultimate explanations.

In this study, coordinated breathing was studied in 13 common bottlenose dolphins because of its links with spontaneous coordinated behaviors (e.g., swimming, foraging, and playing). A strong link was shown between dyadic coordination levels and age/sex categories when both association patterns and spatial formation are considered. This is consistent with a significant influence of social relationships on cooperating and contrasts with an economic perspective based on immediate material outcomes alone. This cooperation bias is explained by linking proximate processes that evoke performance with ultimate evolutionary processes driven by long-term adaptive outcomes. Proximate processes can include 2 kinds of immediate outcomes: material reinforcements and affective states associated with acts of cooperating that can provide positive reinforcement regardless of immediate material benefits (e.g., when there is a time lag between cooperative acts and material outcomes). Affective states can then be adaptive by strengthening social relationships that lead to eventual gains in fitness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Indexical and referential pointing in chimpanzees (Pan troglodytes).

The spontaneous index finger and other referential pointing in 3 adult, laboratory chimpanzees (Pan troglodytes) who have not received language training is reported. Of 256 total observed points, 254 were emitted in the presence of a human to objects in the environment; therefore, the points were communicative. Indicators of intentional communication used by the subjects included attention-getting behaviors, gaze alternation, and persistence until reward. Thus, pointing by these chimpanzees was intentionally communicative. These data imply that perspective-taking and referential communication are generalized hominoid traits, given appropriate eliciting contexts. Index finger pointing was more frequent with the subjects' dominant hands. This study refutes claims that indexical or referential pointing is species-unique to humans or dependent on linguistic competence or explicit training. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perception and generalization of frequency contours by a bottlenose dolphin (Tursiops truncatus).

A single adult female bottlenose dolphin was tested in a series of perceptual studies. On each trial, 4 sine-wave tones were presented that contained a falling frequency contour or some other contour. There were several frequency-transposed exemplars of each contour type in each experiment. The dolphin discriminated contours at a level significantly greater than chance in all experiments. In the 1st 2 experiments, the dolphin demonstrated only modest transfer to novel stimuli and a sensitivity to the absolute frequency of stimuli. In the 3rd experiment, there was no effect of the absolute frequency of stimuli; in the 4th experiment, the dolphin successfully transferred the discrimination to novel stimuli drawn from the octave above the previously heard range. These results demonstrate dolphins' capability to perceive frequency contours, which may underlie the recognition of conspecific whistles. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cardiac response to acoustic playback experiments in the captive bottlenose dolphin (Tursiops truncatus).

Acoustic recordings were used to investigate the cardiac responses of a captive dolphin (Tursiops truncatus) to sound playback stimuli. A suction-cup hydrophone placed on the ventral midline of the dolphin produced a continuous heartbeat signal while the dolphin was submerged. Heartbeats were timed by applying a matched-filter to the phonocardiogram. Significant heart rate accelerations were observed in response to playback stimuli involving conspecific vocalizations compared with baseline rates or tank noise playbacks. This method documents that objective psychophysiological measures can be obtained for physically unrestrained cetaceans. In addition, the results are the 1st to show cardiac responses to acoustic stimuli from a cetacean at depth. Preliminary evidence suggests that the cardiac response patterns of dolphins are consistent with the physiological defense and startle responses in terrestrial mammals and birds. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Human listeners provide insights into echo features used by dolphins (Tursiops truncatus) to discriminate among objects.

Echolocating bottlenose dolphins (Tursiops truncatus) discriminate between objects on the basis of the echoes reflected by the objects. However, it is not clear which echo features are important for object discrimination. To gain insight into the salient features, the authors had a dolphin perform a match-to-sample task and then presented human listeners with echoes from the same objects used in the dolphin's task. In 2 experiments, human listeners performed as well or better than the dolphin at discriminating objects, and they reported the salient acoustic cues. The error patterns of the humans and the dolphin were compared to determine which acoustic features were likely to have been used by the dolphin. The results indicate that the dolphin did not appear to use overall echo amplitude, but that it attended to the pattern of changes in the echoes across different object orientations. Human listeners can quickly identify salient combinations of echo features that permit object discrimination, which can be used to generate hypotheses that can be tested using dolphins as subjects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bottlenose dolphins (Tursiops truncatus) prefer to cooperate when petted: Integrating proximate and ultimate explanations ii.

Cooperation poses theoretical problems because the behaviors of individuals can benefit others. Evolutionary and game-theory explanations that focus on maximizing one's own material outcomes are usually supported by experimental models with isolated and anonymous subjects. Cooperation in the natural world, however, is often a social act whereby familiar individuals coordinate behaviors for shared outcomes. Social cooperation is also associated with a cooperation bias expressed as a preference for cooperation even when noncooperation is immediately more beneficial. The authors report on evidence for such a bias in a captive group of bottlenose dolphins that voluntarily preferred to receive petting from human guides by using a pairwise coordinated approach, even though this was more difficult, and total petting amount was thereby reduced. To explain why this bias occurs, the authors propose an integrated behavioral-evolutionary approach whereby performance is determined by two kinds of immediate outcomes: material gains and intrinsic affective states associated with cooperating. The latter can provide reinforcement when immediate material gains are reduced, delayed, or absent. Over a lifetime, this proximate mechanism can lead to cooperative relationships whose long-term ultimate consequences can be adaptive. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Production and comprehension of referential pointing by orangutans (Pongo pygmaeus).

We report 3 studies of the referential pointing of 2 orangutans (Pongo pygmaeus). Chantek was raised in an enculturated environment; Puti, raised in a nursery, had a more typical captive life. In Experiment 1, flexibility of pointing behavior was investigated by requiring subjects to point in novel circumstances (for an out-of-sight tool, not food). In Experiment 2, we investigated the orangutans' comprehension of the significance of a human point in helping them to locate food. In Experiment 3, we investigated whether these pointing subjects comprehended that a human recipient must be looking for the point to achieve its attention-directing goal. In all experiments the enculturated orangutan showed better understanding of pointing than the captive orangutan. This finding is consistent with recent studies that have found differences in the cognitive and social-cognitive abilities of apes that have had different types of experience with humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dogs' ( Canis familaris ) responsiveness to human pointing gestures.

In a series of 3 experiments, dogs (Canisfamiliaris) were presented with variations of the human pointing gesture; gestures with reversed direction of movement, cross-pointing, and different arm extensions. Dogs performed at above chance level if they could see the hand (and index finger) protruding from the human body contour. If these minimum requirements were not accessible, dogs still could rely on the body position of the signaler. The direction of movement of the pointing arm did not influence the performance. In summary, these observations suggest that dogs are able to rely on relatively novel gestural forms of the human communicative pointing gesture and that they are able to comprehend to some extent the referential nature of human pointing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Determinants of recognition of gestural signs in an artificial language by Atlantic bottle-nosed dolphins (Tursiops truncatus) and humans (Homo sapiens).

Responses of Atlantic bottle-nosed dolphins (Tursiops truncatus) and of humans were collected and analyzed in order to determine the features required for recognition and discrimination of signs (hand signals) in an artificial gestural communication system. Subjects responded to systematically modified signs in which sign components were contrasted for competitive feature salience. One dolphin, with 6 yrs of training in the language, was shown these modified signs intermixed with normal signs in a linguistic, sentence-comprehension context. A second dolphin, familiar with action signs only and with no sentence-comprehension training, served as a nonlingual control. Human subjects were tested in two parallel tasks. The dolphin with sign-language experience attended to (in order of importance) location, completed temporal pattern, gross motor motion, and direction of motion, as salient features. Fine motor motion, hand shape, and hand orientation were less salient. The non-sign-language dolphin attended to all sign features equally and was unaffected by temporal pattern changes. Humans tested in a linguistic context attended to (in order) gross motor motion, location, and an interaction of fine motor motion, hand shape, and hand orientation. Direction of motion and temporal pattern were not salient. Nonlinguistic-context humans attended to all sign features equally and were unaffected by temporal pattern changes. Results indicate that language experience and/or testing context affect feature salience for sign recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Generalization of visual matching by a bottlenosed dolphin (Tursiops truncatus): Evidence for invariance of cognitive performance with visual and auditory materials.

Generalization of a visual matching-to-sample rule was shown in a bottlenosed dolphin, normally considered an auditory specialist. The visual items used were all real-world objects. Some objects had acoustic names in an artificial acoustic language taught to the dolphin named Phoenix. Other objects were unnamed but familiar to Phoenix, and others were objects entirely new to her experience. In Exps 1 and 2, we demonstrated Phoenix's ability to match these objects, from among 2 alternative comparison objects, at levels of 87% correct responses or better, after O-s delay. In Exp 3, Phoenix's matches of familiar and of new objects were better than 94% correct through to delays of 30 s and were 73% correct after a delay of 80 s. In Exp 4, performance was nearly equivalent for statically displayed and dynamically displayed sample objects. Over the 4 experiments, Phoenix matched 16 of 18 objects successfully on the 1st trial that they appeared as samples. From these and other recent findings, it appears that bottlenosed dolphins are capable of carrying out both visual- and auditory-based complex cognitive tasks approximately equally well, a finding at variance with earlier notions of sensory modality limitations in cognitive performance of animals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)