Dolphins (Tursiops truncatus) comprehend the referential character of the human pointing gesture

Bottlenose dolphins are sensitive to human attentional features, including eye functionality

The ability to attribute attentional states to other individuals is a highly adaptive socio-cognitive skill and thus may have evolved in many social species. However, whilst humans excel in this ability, even chimpanzees appear to not accurately understand how visual attention works, particularly in regard to the function of eyes. The complex socio-ecological background and socio-cognitive skill-set of bottlenose dolphins (Tursiops sp.), alongside the specialised training that captive dolphins typically undergo, make them an especially relevant candidate for an investigation into their sensitivity to human attentional states. Therefore, we tested 8 bottlenose dolphins on an object retrieval task. The dolphins were instructed to fetch an object by a trainer under various attentional state conditions involving the trainer's eyes and face orientation: 'not looking', 'half looking', 'eyes open', and 'eyes closed'. As the dolphins showed an increased latency to retrieve the object in conditions where the trainer's head and eyes cued a lack of attention to the dolphin, particularly when comparing 'eyes open' vs 'eyes closed' conditions, we demonstrate that dolphins can be sensitive to human attentional features, namely the functionality of eyes. This study supports growing evidence that dolphins possess highly complex cognitive abilities, particularly those in the social domain.

Information Theory Opens New Dimensions in Experimental Studies of Animal Behaviour and Communication

Over the last 40–50 years, ethology has become increasingly quantitative and computational. However, when analysing animal behavioural sequences, researchers often need help finding an adequate model to assess certain characteristics of these sequences while using a relatively small number of parameters. In this review, I demonstrate that the information theory approaches based on Shannon entropy and Kolmogorov complexity can furnish effective tools to analyse and compare animal natural behaviours. In addition to a comparative analysis of stereotypic behavioural sequences, information theory can provide ideas for particular experiments on sophisticated animal communications. In particular, it has made it possible to discover the existence of a developed symbolic “language” in leader-scouting ant species based on the ability of these ants to transfer abstract information about remote events.

Following the human point: Research with nonhuman animals since Povinelli, Nelson, and Boysen (1990)

For this special issue in honor of Dr. Sarah (Sally) Boysen's career, we review studies on point following in nonhuman animals. Of the 126 papers that we documented on this topic published since the publication of Povinelli, Nelson, and Boysen (1990, Journal of Comparative Psychology, 104, 203-210), 94 (75%) were published in the past 15 years, including 22 in the past 5 years, indicating that this topic is still an active area of interest in the field of animal behavior and cognition. We present results of a survey of publication trends, discussing the species tested and the sample sizes, and we note methodological considerations and current multilaboratory approaches. We then categorize and synthesize the research questions addressed in these studies, which have been at both the ultimate level (e.g., questions related to evolutionary adaptiveness and phylogenetic differences) and proximate level (e.g., questions related to experiential and temperamental processes). Throughout, we consider future directions for this area of research.

Multimodal imitative learning and synchrony in cetaceans: A model for speech and singing evolution

Multimodal imitation of actions, gestures and vocal production is a hallmark of the evolution of human communication, as both, vocal learning and visual-gestural imitation, were crucial factors that facilitated the evolution of speech and singing. Comparative evidence has revealed that humans are an odd case in this respect, as the case for multimodal imitation is barely documented in non-human animals. While there is evidence of vocal learning in birds and in mammals like bats, elephants and marine mammals, evidence in both domains, vocal and gestural, exists for two Psittacine birds (budgerigars and grey parrots) and cetaceans only. Moreover, it draws attention to the apparent absence of vocal imitation (with just a few cases reported for vocal fold control in an orangutan and a gorilla and a prolonged development of vocal plasticity in marmosets) and even for imitation of intransitive actions (not object related) in monkeys and apes in the wild. Even after training, the evidence for productive or "true imitation" (copy of a novel behavior, i.e., not pre-existent in the observer's behavioral repertoire) in both domains is scarce. Here we review the evidence of multimodal imitation in cetaceans, one of the few living mammalian species that have been reported to display multimodal imitative learning besides humans, and their role in sociality, communication and group cultures. We propose that cetacean multimodal imitation was acquired in parallel with the evolution and development of behavioral synchrony and multimodal organization of sensorimotor information, supporting volitional motor control of their vocal system and audio-echoic-visual voices, body posture and movement integration.

Optionality in animal communication: a novel framework for examining the evolution of arbitrariness

A critical feature of language is that the form of words need not bear any perceptual similarity to their function - these relationships can be 'arbitrary'. The capacity to process these arbitrary form-function associations facilitates the enormous expressive power of language. However, the evolutionary roots of our capacity for arbitrariness, i.e. the extent to which related abilities may be shared with animals, is largely unexamined. We argue this is due to the challenges of applying such an intrinsically linguistic concept to animal communication, and address this by proposing a novel conceptual framework highlighting a key underpinning of linguistic arbitrariness, which is nevertheless applicable to non-human species. Specifically, we focus on the capacity to associate alternative functions with a signal, or alternative signals with a function, a feature we refer to as optionality. We apply this framework to a broad survey of findings from animal communication studies and identify five key dimensions of communicative optionality: signal production, signal adjustment, signal usage, signal combinatoriality and signal perception. We find that optionality is widespread in non-human animals across each of these dimensions, although only humans demonstrate it in all five. Finally, we discuss the relevance of optionality to behavioural and cognitive domains outside of communication. This investigation provides a powerful new conceptual framework for the cross-species investigation of the origins of arbitrariness, and promises to generate original insights into animal communication and language evolution more generally.

Conspecific "gaze following" in bottlenose dolphins

"Gaze following"—when one individual witnesses another shift its orientation, and then re-orients in the same direction—has been observed in a wide range of species. Related work with dolphins has to date focused on human–dolphin interactions. In this conspecific study, we examined a group of dolphins orienting, in passing, to gateways between their pools, as opportunities for witnesses to demonstrate "gaze following". Seven bottlenose dolphins were synchronously videotaped on six underwater cameras, for 21 h over three days, and the recordings analyzed by trained observers. The identities of all animals present, their partner state, and whether and to what degree they had altered their access to the gate (e.g., from Monocular to Binocular, or Binocular to Visio-Echoic) was recorded. Compared to animals that did not witness such a change, witnesses of an increase in access by another dolphin were significantly more likely to also act to increase their own access. We observed 460 such cases of "gaze following" in these animals. Dolphins who were partnered (showed sustained swimming within 1 body length) were significantly more likely, than non-partnered animals, to "gaze follow". Dolphins also showed a significant tendency toward matching the kind of access they observed. No significant difference was found in the presence of animals in the back pools, during changes in orientation that were followed, versus in those that were not. These findings support adding bottlenose dolphins to the growing list of species that display conspecific "gaze following".

Investigation on whistle directivity in the Indo-Pacific humpback dolphin (Sousa chinensis) through numerical modeling

Odontocetes have evolved special acoustic structures in the forehead to modulate echolocation and communication signals into directional beams to facilitate feeding and social behaviors. Whistle directivity was addressed for the Indo-Pacific humpback dolphin (Sousa chinensis) by developing numerical models in the current paper. Directivity was first examined at the fundamental frequency 5 kHz, and simulations were then extended to the harmonics of 10, 15, 20, 25, and 30 kHz. At 5 kHz, the -3 dB beam widths in the vertical and horizontal planes were 149.3° and 119.4°, corresponding to the directivity indexes (DIs) of 4.4 and 5.4 dB, respectively. More importantly, we incorporated directivity of the fundamental frequency and harmonics to produce an overall beam, resulting in -3 dB beam widths of 77.2° and 62.9° and DIs of 8.2 and 9.7 dB in the vertical and horizontal planes, respectively. Harmonics can enhance the directivity of fundamental frequency by 3.8 and 4.3 dB, respectively. These results suggested the transmission system can modulate whistles into directional projection, and harmonics can improve DI.

Prosociality and reciprocity in bottlenose dolphins (Tursiops truncatus)

Some moral behaviours, often regarded as reflecting high cognitive abilities (such as empathy, cooperation, targeted helping) are known to only be present in very few species, like great apes, elephants and cetaceans. Prosocial behaviours (producing a benefit for the recipient without necessarily involving a cost for the actor) have been mostly found in primates and, more recently, in elephants. Despite dolphins' reputation for helping their conspecifics, experimental studies about their prosocial and empathic abilities are rare. We conducted Prosocial Choice Tests in six bottlenose dolphins. The subjects had to choose between three objects: choosing the prosocial object induced the simultaneous rewarding of both the subject and a recipient individual; choosing the selfish object induced a reward only for the subject; choosing the null one did not reward anyone. We found prosociality and direct reciprocity in our subjects, and our results suggested that bottlenose dolphins might be able to modulate their prosocial and reciprocal tendencies according to partner-specific information. Subjects seemed to be more prosocial towards the other sex and more reciprocal towards same-sex recipients. This reciprocity might be underpinned by the same features that rule their behaviours in the wild (cooperating with same sex conspecifics). Moreover, an audience effect was reported, as the presence of the subject's young increased subjects' likelihood of prosocial response. Our findings highlighted that prosociality could appear in taxa other than primates, suggesting a convergent evolutionary phenomenon.

The Relevance of Ecological Transitions to Intelligence in Marine Mammals

Macphail's comparative approach to intelligence focused on associative processes, an orientation inconsistent with more multifaceted lay and scientific understandings of the term. His ultimate emphasis on associative processes indicated few differences in intelligence among vertebrates. We explore options more attuned to common definitions by considering intelligence in terms of richness of representations of the world, the interconnectivity of those representations, the ability to flexibly change those connections, and knowledge. We focus on marine mammals, represented by the amphibious pinnipeds and the aquatic cetaceans and sirenians, as animals that transitioned from a terrestrial existence to an aquatic one, experiencing major changes in ecological pressures. They adapted with morphological transformations related to streamlining the body, physiological changes in respiration and thermoregulation, and sensory/perceptual changes, including echolocation capabilities and diminished olfaction in many cetaceans, both in-air and underwater visual focus, and enhanced senses of touch in pinnipeds and sirenians. Having a terrestrial foundation on which aquatic capacities were overlaid likely affected their cognitive abilities, especially as a new reliance on sound and touch, and the need to surface to breath changed their interactions with the world. Vocal and behavioral observational learning capabilities in the wild and in laboratory experiments suggest versatility in group coordination. Empirical reports on aspects of intelligent behavior like problem-solving, spatial learning, and concept learning by various species of cetaceans and pinnipeds suggest rich cognitive abilities. The high energy demands of the brain suggest that brain-intelligence relationships might be fruitful areas for study when specific hypotheses are considered, e.g., brain mapping indicates hypertrophy of specific sensory areas in marine mammals. Modern neuroimaging techniques provide ways to study neural connectivity, and the patterns of connections between sensory, motor, and other cortical regions provide a biological framework for exploring how animals represent and flexibly use information in navigating and learning about their environment. At this stage of marine mammal research, it would still be prudent to follow Macphail's caution that it is premature to make strong comparative statements without more empirical evidence, but an approach that includes learning more about how animals flexibly link information across multiple representations could be a productive way of comparing species by allowing them to use their specific strengths within comparative tasks.

The use of a human's location and social cues by Asian elephants in an object-choice task

Asian elephants have previously demonstrated an ability to follow olfactory cues, but not human-provided social cues like pointing and gazing or orienting to find hidden food (Plotnik et al. in PLoS One 8:e61174, 2013; Anim Behav 88:91-98, 2014). In a study conducted with African elephants, however, elephants were able to follow a combination of these social cues to find food, even when the experimenter's position was counter to the location of the food. The authors of the latter study argued that the differences in the two species' performances might have been due to methodological differences in the study designs (Smet and Byrne in Curr Biol 23(20):2033-2037, 2013). To further investigate the reasons for these potential differences, we partially adapted Smet and Byrne (2013)'s design for a group of Asian elephants in Thailand. In a two-object-choice task in which only one of two buckets was baited with food, we found that, as a group, the elephants did not follow cues provided by an experimenter when she was positioned either equidistant between the buckets or closer to the incorrect bucket when providing the cues. The elephants did, however, follow cues when the experimenter was closer to the correct bucket. In addition, there was individual variability in the elephants' performance within and across experimental conditions. This indicates that in general, for Asian elephants, the pointing and/or gazing cues alone may not be salient enough; local enhancement in the form of the experimenter's position in relation to the food reward may represent a crucial, complementary cue. These results suggest that the variability within and between the species in their performance on these tasks could be due to a number of factors, including methodology, the elephants' experiences with their handlers, ecological differences in how Asian and African elephants use non-visual sensory information to find food in the wild, or some combination of the three.

Sea lions' (Zalophus californianus) use of human pointing gestures as referential cues

This experiment investigated the ability of four human-socialized sea lions to exploit human communicative gestures in three different object-choice tasks based on directional cues emitted by their caretakers. In Study 1, three of the tested subjects were able to generalize their choice of the pointed target to variations of the basic pointing gestures (i.e., cross-body point, elbow point, foot point, and gaze only), from the very first trials. Study 2 showed that the subjects could follow the pointing gestures geometrically and select the correct target among four possible targets, two on each side of the informant. In Study 3, we tested the robustness of their tendency to follow a pointing gesture by hiding targets behind barriers. One subject was able to follow pointing gestures towards targets not visible at the moment of their decision without any training, despite the presence of another visible and directly accessible one. Taken together, these results suggest that sea lions were able to use the referential property of the human pointing gesture, because they were able to rely on extrapolating precise linear vectors along different pointing body parts in order to identify a precise object rather than merely a general direction. These findings support previous arguments that some non-domesticated species might have as great an ability to respond appropriately to pointing gestures as domesticated dogs. The potential roles of human-socialization and specific features of wild sea lions ecology are discussed.

Interpretation of human pointing by African elephants: generalisation and rationality

Factors influencing the abilities of different animals to use cooperative social cues from humans are still unclear, in spite of long-standing interest in the topic. One of the few species that have been found successful at using human pointing is the African elephant (Loxodonta africana); despite few opportunities for learning about pointing, elephants follow a pointing gesture in an object-choice task, even when the pointing signal and experimenter's body position are in conflict, and when the gesture itself is visually subtle. Here, we show that the success of captive African elephants at using human pointing is not restricted to situations where the pointing signal is sustained until the time of choice: elephants followed human pointing even when the pointing gesture was withdrawn before they had responded to it. Furthermore, elephants rapidly generalised their response to a type of social cue they were unlikely to have seen before: pointing with the foot. However, unlike young children, they showed no sign of evaluating the 'rationality' of this novel pointing gesture according to its visual context: that is, whether the experimenter's hands were occupied or not.

Seeing the experimenter influences the response to pointing cues in long-tailed macaques

Methodological variations in experimental conditions can strongly influence animals' performances in cognitive tests. Specifically, the procedure of the so-called object-choice task has been controversially discussed; here, a human experimenter indicates the location of hidden food by pointing or gazing at one of two or more containers. Whereas dogs usually succeed, results for nonhuman primates are ambiguous. In the standard version of the task the majority of subjects do not respond appropriately to human pointing. However, modifying the task setup, such as placing the containers further apart, seems to improve subjects' performances, suggesting that cue salience may be an important variable. Here we investigated whether the visibility of the experimenter inhibits long-tailed macaques' (Macaca fascicularis) usage of the pointing cue. In our baseline condition, with the experimenter fully visible, the monkeys chose the correct container in 61% of the trials. The performance increased significantly, however, when the experimenter was hidden behind a curtain and only the arm of the experimenter, a doll's arm, or a stick was visible. Furthermore, the monkeys performed significantly better when the tip of the pointing finger or device was close to the target compared to the more distant condition. Intriguingly, after these experiments the monkeys' performance was also significantly improved in the baseline condition (70%). Apparently, the monkeys were first distracted by the presence of the experimenter, but then learned to use the cue. These findings highlight the importance of the test conditions, and question some of the assumptions about species-specific differences in the object-choice task.

Are Clark's Nutcrackers (Nucifraga Columbiana) Able to Discriminate Knowledge States of Human Experimenters during an Object-Choice Task?

Corvids and primates have been shown to possess similar cognitive adaptations, yet these animals are seldom tested using similar procedures. Object-choice tasks, which have commonly been used to test whether an animal is able to infer the mental state of a human experimenter based on a gestural cue, provide one potential means of testing these animals using a similar paradigm. The current study used an object-choice task to examine whether the corvid, Clark's nutcracker ( Nucifraga columbiana), is able to use a cognitive strategy to discriminate between the knowledge states of two human experimenters. One experimenter was informed, and the other uninformed, as to the location of a food reward hidden inside one of two opaque containers. During the Uninformed Gesture condition, the nutcrackers were given probe tests during which only the person performing as the uninformed experimenter provided a gesture. Thus, the nutcrackers could not use the experimenter's gesture to reliably find the food. During the Gesture Conflict condition, the nutcrackers were presented with a cue conflict. During probe tests, both the informed and the uninformed experimenter gestured to separate containers. Thus, to find the food the nutcrackers had to use the gesture from the informed experimenter and refrain from using the gesture of the uninformed experimenter. Our results showed that when the uninformed experimenter's gesture was presented alone, the birds continued to follow the gesture even though it was not consistently predictive of the food's location. However, when provided with two conflicting gestures, as a group the nutcrackers responded to the gesture of the informed experimenter at above chance levels. These results suggest that the birds had learned that the gesture was informative, perhaps by associative learning, yet when this mechanism was not reliable the nutcrackers were able to use either the human experimenters' presence/absence during the baiting process, or possibly their knowledge states, to determine which gesture to rely upon.

A cross-species study of gesture and its role in symbolic development: implications for the gestural theory of language evolution

Using a naturalistic video database, we examined whether gestures scaffold the symbolic development of a language-enculturated chimpanzee, a language-enculturated bonobo, and a human child during the second year of life. These three species constitute a complete clade: species possessing a common immediate ancestor. A basic finding was the functional and formal similarity of many gestures between chimpanzee, bonobo, and human child. The child’s symbols were spoken words; the apes’ symbols were lexigrams – non-iconic visual signifiers. A developmental pattern in which gestural representation of a referent preceded symbolic representation of the same referent appeared in all three species (but was statistically significant only for the child). Nonetheless, across species, the ratio of symbol to gesture increased significantly with age. But even though their symbol production increased, the apes continued to communicate more frequently by gesture than by symbol. In contrast, by 15–18 months of age, the child used symbols more frequently than gestures. This ontogenetic sequence from gesture to symbol, present across the clade but more pronounced in child than ape, provides support for the role of gesture in language evolution. In all three species, the overwhelming majority of gestures were communicative (i.e., paired with eye contact, vocalization, and/or persistence). However, vocalization was rare for the apes, but accompanied the majority of the child’s communicative gestures. This species difference suggests the co-evolution of speech and gesture after the evolutionary divergence of the hominid line. Multimodal expressions of communicative intent (e.g., vocalization plus persistence) were normative for the child, but less common for the apes. This species difference suggests that multimodal expression of communicative intent was also strengthened after hominids diverged from apes.

Visual cues given by humans are not sufficient for Asian elephants (Elephas maximus) to find hidden food

Recent research suggests that domesticated species – due to artificial selection by humans for specific, preferred behavioral traits – are better than wild animals at responding to visual cues given by humans about the location of hidden food. \Although this seems to be supported by studies on a range of domesticated (including dogs, goats and horses) and wild (including wolves and chimpanzees) animals, there is also evidence that exposure to humans positively influences the ability of both wild and domesticated animals to follow these same cues. Here, we test the performance of Asian elephants (Elephas maximus) on an object choice task that provides them with visual-only cues given by humans about the location of hidden food. Captive elephants are interesting candidates for investigating how both domestication and human exposure may impact cue-following as they represent a non-domesticated species with almost constant human interaction. As a group, the elephants (n = 7) in our study were unable to follow pointing, body orientation or a combination of both as honest signals of food location. They were, however, able to follow vocal commands with which they were already familiar in a novel context, suggesting the elephants are able to follow cues if they are sufficiently salient. Although the elephants’ inability to follow the visual cues provides partial support for the domestication hypothesis, an alternative explanation is that elephants may rely more heavily on other sensory modalities, specifically olfaction and audition. Further research will be needed to rule out this alternative explanation.

Test sensitivity is important for detecting variability in pointing comprehension in canines

Several articles have been recently published on dogs' (Canis familiaris) performance in two-way object choice experiments in which subjects had to find hidden food by utilizing human pointing. The interpretation of results has led to a vivid theoretical debate about the cognitive background of human gestural signal understanding in dogs, despite the fact that many important details of the testing method have not yet been standardized. We report three experiments that aim to reveal how some procedural differences influence adult companion dogs' performance in these tests. Utilizing a large sample in Experiment 1, we provide evidence that neither the keeping conditions (garden/house) nor the location of the testing (outdoor/indoor) affect a dogs' performance. In Experiment 2, we compare dogs' performance using three different types of pointing gestures. Dogs' performance varied between momentary distal and momentary cross-pointing but "low" and "high" performer dogs chose uniformly better than chance level if they responded to sustained pointing gestures with reinforcement (food reward and a clicking sound; "clicker pointing"). In Experiment 3, we show that single features of the aforementioned "clicker pointing" method can slightly improve dogs' success rate if they were added one by one to the momentary distal pointing method. These results provide evidence that although companion dogs show a robust performance at different testing locations regardless of their keeping conditions, the exact execution of the human gesture and additional reinforcement techniques have substantial effect on the outcomes. Consequently, researchers should standardize their methodology before engaging in debates on the comparative aspects of socio-cognitive skills because the procedures they utilize may differ in sensitivity for detecting differences.

Do owners have a clever hans effect on dogs? Results of a pointing study

Dogs are exceptionally successful at interpreting human pointing gestures to locate food hidden in one of two containers. However, it has repeatedly been questioned whether dogs rely on the pointing gesture or their success is increased by subtle cues from their human handler. In two experiments we used a standard two-way object-choice task to focus on this potential Clever Hans effect. We investigated if and how owners' knowledge and beliefs influenced their dogs' performance. In two experiments, as is typical in such pointing tasks, the owners sat behind their dogs, in close auditory and tactile contact with them. In Experiment 1, we systematically manipulated the owners' knowledge of whether or not their dog should follow the pointing gesture, but at the same time instructed the owners to refrain from influencing the choice of their dog. We found no influence of subtle cues from the owners, if indeed they existed: dogs in the different groups followed the pointing uniformly. Furthermore, in the absence of pointing dogs chose randomly, even though the owners had been informed about the location of the reward. In Experiment 2, owners were instructed to actively influence the choice of their dogs, and they, indeed, succeeded in sending their dogs to the container they believed to be baited. However, their influence was significantly weaker if the experimenter had previously pointed to the other location. Overall the pointing gesture seems to have a strong effect on the choice of dogs in an object-choice task. Pointing can lead the dogs to success without help from their owners as well as it can counteract clear directional instructions provided by the owners.

Man's underground best friend: domestic ferrets, unlike the wild forms, show evidence of dog-like social-cognitive skills

Recent research has shown that dogs’ possess surprisingly sophisticated human-like social communication skills compared to wolves or chimpanzees. The effects of domestication on the emergence of socio-cognitive skills, however, are still highly debated. One way to investigate this is to compare socialized individuals from closely related domestic and wild species. In the present study we tested domestic ferrets (Mustela furo) and compared their performance to a group of wild Mustela hybrids and to domestic dogs (Canis familiaris). We found that, in contrast to wild Mustela hybrids, both domestic ferrets and dogs tolerated eye-contact for a longer time when facing their owners versus the experimenter and they showed a preference in a two-way choice task towards their owners. Furthermore, domestic ferrets, unlike the wild hybrids, were able to follow human directional gestures (sustained touching; momentary pointing) and could reach the success rate of dogs. Our study provides the first evidence that domestic ferrets, in a certain sense, are more dog-like than their wild counterparts. These findings support the hypothesis that domestic species may share basic socio-cognitive skills that enable them to engage in effectively orchestrated social interactions with humans.

How two word-trained dogs integrate pointing and naming

Two word-trained dogs were presented with acts of reference in which a human pointed, named objects, or simultaneously did both. The question was whether these dogs would assume co-reference of pointing and naming and thus pick the pointed-to object. Results show that the dogs did indeed assume co-reference of pointing and naming in order to determine the reference of a spoken word, but they did so only when pointing was not in conflict with their previous word knowledge. When pointing and a spoken word conflicted, the dogs preferentially fetched the object by name. This is not surprising since they are trained to fetch objects by name. However, interestingly, in these conflict conditions, the dogs fetched the named objects only after they had initially approached the pointed-to object. We suggest that this shows that the word-trained dogs interpret pointing as a spatial directive, which they integrate into the fetching game, presumably assuming that pointing is relevant to finding the requested object.

Directional properties of bottlenose dolphin (Tursiops truncatus) clicks, burst-pulse, and whistle sounds

The directional properties of bottlenose dolphin clicks, burst-pulse, and whistle signals were measured using a five element array, at horizontal angles of 0°, 45°, 90°, 135°, and 180° relative to a dolphin stationed on an underwater biteplate. Clicks and burst-pulse signals were highly directional with directivity indices of ~11 dB for both signal types. Higher frequencies and higher amplitudes dominated the forward, on-axis sound field. A similar result was found with whistles, where higher frequency harmonics had greater directivity indices than lower frequency harmonics. The results suggest the directional properties of these signals not only provide enhanced information to the sound producer (as in echolocation) but can provide valuable information to conspecific listeners during group coordination and socialization.

A comparative approach to dogs' (Canis familiaris) and human infants' comprehension of various forms of pointing gestures

We investigated whether dogs and 2-, and 3-year-old human infants living, in some respects, in very similar social environments are able to comprehend various forms of the human pointing gesture. In the first study, we looked at their ability to comprehend different arm pointing gestures (long cross-pointing, forward cross-pointing and elbow cross-pointing) to locate a hidden object. Three-year-olds successfully used all gestures as directional cues, while younger children and dogs could not understand the elbow cross-pointing. Dogs were also unsuccessful with the forward cross-pointing. In the second study, we used unfamiliar pointing gestures i.e. using a leg as indicator (pointing with leg, leg cross-pointing, pointing with knee). All subjects were successful with leg pointing gestures, but only older children were able to comprehend the pointing with knee. We suggest that 3-year-old children are able to rely on the direction of the index finger, and show the strongest ability to generalize to unfamiliar gestures. Although some capacity to generalize is also evident in younger children and dogs, especially the latter appear biased in the use of protruding body parts as directional signals.

A claim in search of evidence: reply to Manger's thermogenesis hypothesis of cetacean brain structure

In a recent publication in Biological Reviews, Manger (2006) made the controversial claim that the large brains of cetaceans evolved to generate heat during oceanic cooling in the Oligocene epoch and not, as is the currently accepted view, as a basis for an increase in cognitive or information-processing capabilities in response to ecological or social pressures. Manger further argued that dolphins and other cetaceans are considerably less intelligent than generally thought. In this review we challenge Manger's arguments and provide abundant evidence that modern cetacean brains are large in order to support complex cognitive abilities driven by social and ecological forces.

Evidence of teaching in Atlantic spotted dolphins (Stenella frontalis) by mother dolphins foraging in the presence of their calves

Teaching is a powerful form of social learning, but there is little systematic evidence that it occurs in species other than humans. Using long-term video archives the foraging behaviors by mother Atlantic spotted dolphins (Stenella frontalis) were observed when their calves were present and when their calves were not present, including in the presence of non-calf conspecifics. The nine mothers we observed chased prey significantly longer and made significantly more referential body-orienting movements in the direction of the prey during foraging events when their calves were present than when their calves were not present, regardless of whether they were foraging alone or with another non-calf dolphin. Although further research into the potential consequences for the naïve calves is still warranted, these data based on the maternal foraging behavior are suggestive of teaching as a social-learning mechanism in nonhuman animals.

Bottlenose dolphins understand relationships between concepts

We dispute Penn et al.'s claim of the sharp functional discontinuity between humans and nonhumans with evidence in bottlenose dolphins (Tursiops truncatus) of higher-order generalizations: spontaneous integration of previously learned rules and concepts in response to novel stimuli. We propose that species-general explanations that are “bottom-up” in approach are more plausible than Penn et al.'s innatist approach of a genetically prespecified supermodule.

Comprehension of human pointing gestures in horses (Equus caballus)

Twenty domestic horses (Equus caballus) were tested for their ability to rely on different human gesticular cues in a two-way object choice task. An experimenter hid food under one of two bowls and after baiting, indicated the location of the food to the subjects by using one of four different cues. Horses could locate the hidden reward on the basis of the distal dynamic-sustained, proximal momentary and proximal dynamic-sustained pointing gestures but failed to perform above chance level when the experimenter performed a distal momentary pointing gesture. The results revealed that horses could rely spontaneously on those cues that could have a stimulus or local enhancement effect, but the possible comprehension of the distal momentary pointing remained unclear. The results are discussed with reference to the involvement of various factors such as predisposition to read human visual cues, the effect of domestication and extensive social experience and the nature of the gesture used by the experimenter in comparative investigations.

Cetaceans have complex brains for complex cognition

A group of eminent cetacean researchers respond to headlines charging that dolphins might be "flippin' idiots". They examine behavioural, anatomical and evolutionary data to conclude that the large brain of cetaceans evolved to support complex cognitive abilities.

A comparative study of the use of visual communicative signals in interactions between dogs (Canis familiaris) and humans and cats (Felis catus) and humans

Dogs' (Canis familiaris) and cats' (Felis catus) interspecific communicative behavior toward humans was investigated. In Experiment 1, the ability of dogs and cats to use human pointing gestures in an object-choice task was compared using 4 types of pointing cues differing in distance between the signaled object and the end of the fingertip and in visibility duration of the given signal. Using these gestures, both dogs and cats were able to find the hidden food; there was no significant difference in their performance. In Experiment 2, the hidden food was made inaccessible to the subjects to determine whether they could indicate the place of the hidden food to a naive owner. Cats lacked some components of attention-getting behavior compared with dogs. The results suggest that individual familiarization with pointing gestures ensures high-level performance in the presence of such gestures; however, species-specific differences could cause differences in signaling toward the human.

A comparative analysis of animals' understanding of the human pointing gesture

We review studies demonstrating the ability of some animals to understand the human pointing gesture. We present a 3-step analysis of the topic. (1) We compare and evaluate current experimental methods (2) We compare available experimental results on performance of different species and investigate the interaction of species differences and other independent variables (3) We evaluate how our present understanding of pointing comprehension answers questions about function, evolution and mechanisms. Recently, a number of different hypotheses have been put forward to account for the presence of this ability in some species and for the lack of such comprehension in others. In our view, there is no convincing evidence for the assumption that the competitive lifestyles of apes would inhibit the utilization of this human gesture. Similarly, domestication as a special evolutionary factor in the case of some species falls short in explaining high levels of pointing comprehension in some non-domestic species. We also disagree with the simplistic view of describing the phenomenon as a simple form of conditioning. We suggest that a more systematic comparative research is needed to understand the emerging communicative representational abilities in animals that provide the background for comprehending the human pointing gesture.

Human Listeners Are Able to Classify Dog (Canis familiaris) Barks Recorded in Different Situations

The authors investigated whether human listeners could categorize played-back dog (Canis familiaris) barks recorded in various situations and associate them with emotional ratings. Prerecorded barks of a Hungarian herding dog breed (Mudi) provided the sample. Human listeners were asked to rate emotionality of the vocalization and to categorize the situations on the basis of alternative situations provided on a questionnaire. The authors found almost no effect of previous experience with the given dog breed or of owning a dog. Listeners were able to categorize bark situations high above chance level. Emotionality ratings for particular bark samples correlated with peak and fundamental frequency and interbark intervals. The authors did not find a significant effect of tonality (harmonic-to-noise ratio) on either the emotionality rating or situation categorization of the human listeners. Humans' ability to recognize meaning suggests that barks could serve as an effective means of communication between dog and human.

Bottlenosed dolphins (Tursiops truncatus) comprehend the referent of both static and dynamic human gazing and pointing in an object-choice task

The authors tested 2 bottlenosed dolphins (Tursiops truncatus) for their understanding of human-directed gazing or pointing in a 2-alternative object-choice task. A dolphin watched a human informant either gazing at or pointing toward 1 of 2 laterally placed objects and was required to perform a previously indicated action to that object. Both static and dynamic gaze, as well as static and dynamic direct points and cross-body points, yielded errorless or nearly errorless performance. Gaze with the informant's torso obscured (only the head was shown) produced no performance decrement, but gaze with eyes only resulted in chance performance. The results revealed spontaneous understanding of human gaze accomplished through head orientation, with or without the human informant's eyes obscured, and demonstrated that gaze-directed cues were as effective as point-directed cues in the object-choice task.

Enhanced nutrition of offspring as a crucial factor for the evolution of intelligence on land

Whilst life in the sea is undoubtedly an ancient process organisms with an exclusively marine lineage have not evolved the degree of intelligence demonstrated by the most advanced terrestrial species. Among the differences between terrestrial and marine environments which may begin to account for this is the instability of the terrestrial environment in comparison to the ocean. Unlike the ocean, terrestrial environments are not buffered against rapid changes in temperature, available water and other environmental extremes. This represents a challenge for the vulnerable offspring of terrestrial species. Evolutionary adaptation to this challenge has included greater transfer of resources from adult to offspring, as demonstrated by terrestrial vertebrates. However the evolution of mechanisms allowing enhanced transfer of resources between generations also creates conditions whereby offspring can be born with larger and more costly brains, developed and nourished from the outset even when they are not likely to prove useful until later life. As nutrition of offspring on land improved through natural selection better brains may thereby have been facilitated, with subsequent evolution driven by proximate selective pressures. The culmination of this process may be seen in the enormous transfer of resources from parents to offspring characteristic of humans and the advanced intelligence associated with them. Medical implications of this theory include the possible impact on the maternal brain of increased transfer of resources to the developing brain during pregnancy and lactation. This could help to account for the observed association between mental illness and the puerperium.