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Open Access Publications from the University of California


The International Journal of Comparative Psychology is sponsored by the International Society for Comparative Psychology. It is a peer-reviewed open-access digital journal that publishes studies on the evolution and development of behavior in all animal species. It accepts research articles and reviews, letters and audiovisual submissions.

Volume 30, 2017

Research Article

Male Mate Choice Among Captive Long-tailed Macaques (Macaca Fascicularis)

The purpose of this study was to investigate male preference and to define the aspects of females that affect male preference. We set experimental conditions that enabled us to measure successful mating by gathering sperm from female vaginal washings and observing sexual behavior. The animal subjects in our study were cynomolgus monkeys, all of whom were bred in our primate institute. During the study, one male would be grouped with two females, each of whom lived in a cage adjacent to the male’s cage. This enabled each of the females to be housed with the male in turn; 12 males and 24 females were included in the study. After a male was housed with a female, we observed through a microscope the existence of sperm in the female’s vaginal washing, thus confirming copulation success. In some of the groups, behavioral observation was conducted on both the male and female subjects. According to our findings, in the multiparous females, successful mating was observed on 29% of cohabitation days. Among nulliparous females, the presence of sperm was observed on only 6% of cohabitation periods. Some 66.7% of nulliparous females never mated with a male. Our observations also revealed that sexual behaviors were more frequently observed when a male lived with a multiparous female. “Male-grooming-of-female” activities were seen more frequently between a male and multiparous female; that is, the male approached a multiparous female for copulation by grooming her. Our study suggests that male cynomolgus monkeys prefer multiparous females, as it is important that a male choose a female who more easily and regularly becomes pregnant and gives birth to offspring with a higher survival rate. Thus, male choice is biologically significant with respect to leaving more offspring.

The valuation cost decreases as a function of extended exposure to a risky-choice procedure

Several studies in pigeons and rats have reported a predictable relation between latencies during no-choice trials and the ulterior preference in choice trials. The Sequential Choice Model (SCM) was proposed in 2008 to account for these results, and more importantly to make precise predictions about the correlation between latency and preference. Eight male Wistar rats were exposed to 48 sessions in a risk-sensitive procedure, each session was composed by 10 blocks of trials (2 no-choice and 4 choice trials). We analyzed data taking latencies of response and testing the SCM’s predictions. Our data support partially the SCM’s predictions, but a monotonic decrease to a floor effect in all latencies of response does not allow confirming all predictions. The results are discussed regarding a decrease in the valuation cost as a result of extended exposure, and arguing that diminishing latencies in this particular procedure contributed to increase the whole rate of reinforcement.

Object manipulation and play behavior in bottlenose dolphins (Tursiops truncatus) under human care

Cetaceans are well-known to display various play activities: numerous scientific papers have documented this phenomenon in wild populations and for delphinids under human care. The present study describes analyses of bottlenose dolphin ( Tursiops truncatus ) interactions with man-made objects introduced to their habitat as part of an environmental enrichment program. At Parc Asterix Delphinarium (France), 9 bottlenose dolphins were presented with 21 different objects. During 17 hours and using object-focal follows, we studied the dolphins’ behaviors directed toward the objects, according to the objects physical properties (i.e. complexity and buoyancy). We also documented the body parts the animals used to manipulate the objects. The results show that young dolphins displayed more playful actions towards the introduced objects than their older conspecifics. In general, subjects preferred the objects classified as simple and floating, they displayed a larger variety of behaviours, they spent more time and were more creative with them than with other types of objects. Finally, there was significantly more contact and “manipulation” with the dolphin head area than with the fins, fluke or other body parts. By analyzing the dolphins’ behaviors and actions they directed towards the introduced objects, the present study discusses meanings dolphins might give to their surroundings and the relevance of play behavior to their welfare.

Rest in the Zebrafish

The purpose and function of sleep has been the topic of discussion for several centuries.  Though our understanding of the mechanisms underlying the propagation and maintenance of rest states has undergone significant improvement, much remains to be learned with regards to the effects of disrupted sleep on diseased states.  A deeper understanding of the neural circuitry and associated phenotypes would allow for the identification of sleep-related pathologies as well as the development of therapies for individuals with sleep disorders. To this end, the zebrafish ( danio rerio ) pose a great advantage.  In the adult animal, sleep is largely consolidated to dark phases.  Sleep may be disrupted via environmental, pharmacological or genetic manipulations.  Disrupted sleep rhythms in the adult animal are linked to changes in gene and protein expression, while behavioral measures of anxiety have produced mixed results. We propose that this variation is a result of the type of sleep disruption as well as the type of anxiety test employed.  This beckons the need for further study of the effects of environmental and pharmacological manipulations on the sleep rhythms of the animal.  Further, researchers must not rely solely on one test as a measure of stress or anxiety as it provides only a one-dimensional insight.

Adult-juvenile play fighting in rats: Insight into the experiences that facilitate the development of socio-cognitive skills

Rats reared with playful peers during the juvenile period have a modified prefrontal cortex and improved executive functions, whereas ones reared with less playful partners, such as an adult, do not. It has been hypothesized that peer-peer play fighting creates unique experiences that tax executive functions and so influence the refinement of the prefrontal cortex. The present study compares the rough-and-tumble play of juveniles interacting with another peer with that of juveniles interacting with an adult. The juveniles interacting with adults engage in as much play as those that interact with juveniles. However, they experience fewer attacks from their adult partners and experience fewer bouts of close-quarter wrestling. Moreover, the juveniles in these juvenile-adult pairs experience fewer opportunities to perform role reversals in which the attacker becomes the defender. These findings support the hypothesis that the turn taking typical of the play fighting with peers is critical for the development of executive functions.

Do pinnipeds have personality? Broad dimensions and contextual consistency of behavior in harbor seals (Phoca vitulina) and California sea lions (Zalophus californianus).

Personality has now been studied in species as diverse as chimpanzees and cuttlefish, but marine mammals remain vastly underrepresented in this area. A broad range of traits have been assessed only once in each of bottlenose dolphins and California sea lions, while consistent individual differences in a few specific behaviors have been identified in grey seals. Furthermore, the context component of definitions of personality is not often assessed, despite evidence that animals may show individual patterns of behavioral consistency across contexts. The current study therefore aimed to use behavioral coding to assess underlying personality factors and consistency across contexts in two marine mammal species: California sea lions and harbor seals. In both species, two personality factors were extracted using exploratory factor analysis. Both were broadly similar across species; the first, Boldness, resembled human Extraversion, and to some extent Openness, with sea lions exhibiting a greater social component. The second factor was labeled Routine Activity, and may contain some Conscientiousness-like traits. Species-specific patterns were also identified for interactive behaviors across two contexts. However, there was substantial individual variation in the frequency of these behaviors, as well as some animals who did not conform to group-level trends. This study therefore provides novel evidence for broad personality factors and both group- and individual-level patterns of contextual consistency in two pinniped species.

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Special Issue: Exploring the Intersection of Comparative and Clinical Psychology

Exploring the Intersection of Comparative and Clinical Psychology: An Introduction

This article serves as the introduction to the special issues of the International Journal of Comparative Psychology on the intersection of comparative and clinical psychology.  These two fields have a shared history going back to the beginnings of each.  Prominent names throughout psychology have work that crosses over between these two fields.  Freud referenced Darwin’s work throughout his work and Skinner’s research was almost exclusively comparative psychology research.  For much of the first half of the last century there was a clear collaboration between the two fields that was fueled by motivation to find the best ways of understanding psychological processes.  That collaboration has slowed considerably in the past several decades and this has coincided with increased specialization and compartmentalization throughout psychology.  It is hoped that the important articles included in this special issue will help spark further discussion of how these two fields can again collaborate for mutual professional benefit and for the benefit for the general public.

Comparative Psychopathology: Connecting Comparative and Clinical Psychology

The animal welfare movement was empowered by decades of animal studies focused on the ontogeny of psychopathology in non-human primates and other species. When H.F. Harlow induced aberrant behaviors in rhesus macaques, collaborators began the search for effective behavioral and psychopharmacological interventions. Years later, working with human subjects in his clinical practice, Harlow’s first graduate student, A.H. Maslow developed a “Hierarchy of Needs” and the hypothetical construct of self-actualization.  Following Harlow’s practice of using human models to design monkey studies, present day psychologists apply what is known about maladaptive behavior and the factors that facilitate positive human behavior to improve the quality of life for non-human taxa living in captive settings.  We know how to prevent psychopathology in monkeys and apes but nonhuman primates are still confined in restricted, substandard facilities that introduce trauma and suffering. Felids, ursids, elephants and cetaceans have also suffered this fate. As a result, there is good reason for clinical and comparative psychologists to collaborate to ameliorate aberrant behaviors while creating conditions that enable all captive animals to thrive.

The Importance of Chimpanzee Personality Research to Understanding Processes Associated with Human Mental Health

Personality research seeks to identify and understand underlying process associated with individual differences in dispositional traits. In humans, individual variation across personality traits have been found to associate with  mental health outcomes often times via common neurobiological processes.  This shared neurobiological basis demonstrates the value of personality research in elucidating processes associated with mental disorders. More recently, a burgeoning animal personality literature has made efforts to elucidate neurobiological and environmental mechanisms associated with variation in personality—within this literature, chimpanzees ( Pan troglodytes ) represent the most promising model species with respect to optimal translational value to humans. The purpose of the current paper was thus to review the chimpanzee personality literature, with particular emphasis on the organizational, genetic, environmental, and neuroscientific basis of individual variation in personality. We further present a primate-translational operationalization of personality pathology underscoring the notion that personality pathology is rooted within basic dispositions, with evidence of genetic and environmental contributions to such tendencies. Finally, benefits with regard to animal welfare and the National Institute of Mental Health’s Research Domain Criteria (RDoC) Initiative, as well as roadblocks associated with curtailment of research involving captive chimpanzees are reviewed. In sum, the current review highlights the importance of translational personality research with chimpanzees as an unparalleled animal model for investigations into the pathophysiology of human mental health.

Resistance to Extinction and Psychopathology, With New Evidence of How a CS Can Act Like a US in The Sexual conditioning of Male Japanese Quail (Coturnix Coturnix Japonica)

This paper is organized in three sections. In the first section, we discuss the relevance of comparative psychology to clinical issues by relating resistance to extinction to psychological disorders involving anxiety, addiction, and fetishism. In the second section, we review areas of comparative psychology that deal in one way or another with the general problem of treating an insignificant event as it were significant. We describe research on supernormal stimuli, evaluative conditioning, acquired drives, incentive sensitization, and consummatory response theory. In the third section of the paper, we present new research on second-order sexual conditioning of male Japanese quail related to the consummatory response theory. First-order conditioning was conducted by pairing the presentation of a terrycloth object (CS1 or conditioned stimulus 1) with copulation with a female (the US or unconditioned stimulus). The male quail came to approach the terrycloth object during the first-order conditioning phase. In addition, about half of the quail also showed conditioned consummatory responses directed towards the terrycloth object. During the second-order conditioning phase, the terrycloth object was used to condition responding to a light (CS2) in the absence of further exposures to the unconditioned stimulus. Birds that showed conditioned consummatory behavior towards CS1 persisted in this behavior during the second-order phase and showed successful second-order conditioning of the light. In contrast, birds that failed to develop conditioned consummatory responses to CS1 showed rapid extinction and minimal second-order conditioning. The implications of these finding for learning theory and for psychopathology are discussed.

Role of animal models in the development of behavioral treatment for bipolar disorder

Bipolar disorder is difficult to capture in a single animal model, so far proving impossible.  Models have evaluated the neurobiological, genetic, pharmacological and behavioral aspects, both in seclusion and in various combinations, but have yet to prove construct or face validity or led to highly effective treatment models.   One area where animal models are having success is when animal models shape behavioral treatment.  Third wave behavioral therapies and Applied Behavior Analysis (ABA) have shown decreased relapse and re-hospitalization at 1 year follow up, increased medication compliance and increased family support.  Cognitive Behavior Therapy (CBT), Dialectal Behavior Therapy (DBT) and Family Focused Treatment (FFT) that include problem solving, family education and self-management have shown success across setting such as school, home and community, especially when used as part of the overall treatment package with medication. While a single model is unable to encompass all areas of need for a disorder as complex as bipolar disorder, continued research should allow for new treatment models to emerge.

Keywords :  Bipolar disorder, animal models, cognitive behavior therapy, dialectical behavior therapy, applied behavior analysis, family focused therapy

Stan Kuczaj Tribute

The Legacy Lives on, a Year Later: Dr. Stan A. Kuczaj A Special Issue – Part 2

The scientific community has mourned the loss of Dr. Stan Kuczaj, Professor at The University of Southern Mississippi and Director of the Marine Mammal Behavior and Cognition Laboratory, for the past year. In this time of grieving and reminiscing, his scientific legacy has continued to live on through students, collaborators and trusted colleagues.  Stan’s passing has acted in part as a motivator to continue to publish works that he invested time and energy in as a tribute, seeing his visions through to fruition. In addition to publishing droves of literature, his colleagues within the development and comparative fields have bound together for the common goal of advancing the science through new collaborations, merged resources, and tackling innovative topics in comparative studies. This second commemorative special issue is a testament to the vast scope of Stan’s impact on the scientific community, as well as his legacy that each of his students and colleagues continues to cultivate. Ten additional papers round out our initial tribute to Dr. Stan Kuczaj in honor of his lifetime achievements.

A Killer Whale’s (Orcinus orca) Response to Visual Media

Environmental enrichment is critical for maintaining cognitive welfare for animals in human care but is subject to individual preferences.  The interest in a video-based enrichment was assessed for a single killer whale ( Orcinus orca ) in human care.  The adult female was presented 20 video recordings featuring cetaceans, elephants, or humans with each video presented in two conditions: (1) with sound and (2) without sound.  Four additional presentations in which the television displayed a blank screen served as controls.  All sessions were videotaped and coded for time spent viewing the recordings, behavioral responses, and visual laterality.  The killer whale spent significantly more time at the television when programs were on screen compared to when the television was present but blank.  She was more likely to watch videos accompanied by sound than those presented without sound. Videos were more likely to be viewed monocularly rather than binocularly, with a right eye preference when viewing the videos the first time they were presented.  The highest rates of behavioral responses occurred during videos of cetaceans.  These results demonstrate that one killer whale responded to video recordings of different stimuli, suggesting that video recordings may be used as a form of enrichment for cetaceans and that not all video content and formats are equally interesting.

Does Personality Similarity in Bottlenose Dolphin Pairs Influence Dyadic Bond Characteristics?

Social structures are critical to the success of many species and have repercussions on health, well-being, and adaptation, yet little is known about the factors which shape these structures aside from ecology and life history strategies. Dyadic bonds are the basis of all social structures; however, mechanisms for formations of specific bonds or patterns in which individuals form which types of bonds have yet to be demonstrated. There is a variety of evidence indicating personality may be a factor in shaping bonds, but this relationship has not been explored with respect to bond components and is yet to be demonstrated in dolphins. This study utilizes a captive population in a naturalistic environment to test for correlation between similarity within the dyad along each personality factor and the strength of the dyad’s bond characteristics. Personality was assessed using a Five Factor Model questionnaire. Dyadic bond strength and characteristic qualities were determined through an exploratory factor analysis to group behaviors recorded via underwater opportunistic focal-follow video. Discovered bond components differed from previous studies and were termed affiliative support, sociosexual, and conflict play.  Individuals who differed in Extraversion and Neuroticism displayed greater levels of bonding. This study expands our understanding of the formation of bonds between individuals and the evolution of social structure. Furthermore, it better equips us for making informed environmental policy decisions and improving captive animal care.

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Evaluation of a developing ecotourism industry: Whale watching in the Gulf of Tribugá, Colombia

The ecotour industry continues to grow with a distinct focus on providing the public with up-close encounters with cetaceans. As a result, research focusing on both the effects of ecotourism on cetaceans and the efficacy of conservation-focused educational interventions for whale-watching operators is necessary to monitor and develop industry standards. Each year, whale-watching tours target humpback whales along their Colombian Pacific breeding grounds. There are many benefits to ecotourism in this area, including the use of whale-watching vessels as a platform for scientific research and environmental education. However, some whale-watching operators may lack species-specific knowledge and/or do not follow the suggested industry guidelines. Researchers held educational seminars for whale-watching staff at six hotels that border the Gulf of Tribugá. Seminars focused on whale anatomy, behavior, anthropogenic effects on the species , and sustainable whale-watching protocols. Participants were asked to complete a questionnaire aimed to assess constructs related to the conservation of this species. This self-report information was accompanied by implicit measures (e.g., sighting duration, distance from whales) recorded during tours in situ. Behavioral observations aimed at assessing whales’ response to ecotour vessels demonstrated that whales increased rates of surface-active behaviors (e.g., tail slashes) with increasing nearness and duration. Whale-watching operators’ conduct during sightings demonstrated that positive attitudes toward humpback whales did not translate into adherence to sustainable practices. This relationship between the whale-watching operators’ questionnaire results and their behavior in the field demonstrates the need for careful monitoring of this developing industry. This project represents a preliminary evaluation of this budding ecotour industry. Continued efforts to increase knowledge while promoting self-advocacy, positive perceived behavioral control, subjective norms, behavioral intentions, and attitudes towards these animals will enable the safeguarding of near-shore waters essential for breeding and nursing humpback whales.

Thunks: Evidence for Varied Harmonic Structure in an Atlantic Bottlenose Dolphin (Tursiops truncatus) Sound

McCowan and Reiss first reported the “thunk” sound of the Atlantic bottlenose dolphin ( Tursiops truncatus ) during separations and discipline behavior of mother-calf dyads. This sound has been previously described as a wide-band, low frequency contact call, however the harmonic structure of this sound is more variable than previously described. Based on preliminary observations of the graded structure of thunks within our data set, we investigated the directionality of thunks with energies at higher frequencies. We recorded a bottlenose dolphin mother with her calf during the first 30-days of life, and analyzed thunk production during separation and discipline contexts. Two classifications of the thunk sound were compared to determine calf response and whether location cues were embedded in the higher harmonics of one of the thunk types. The mother oriented towards the calf significantly more during production of both thunk types during separation and discipline contexts. This sound may have potential directional information within the harmonic structure; however, we could not draw that conclusion based on our findings. Therefore, we present data here that indicates a graded structure to the harmonics of thunk sounds.

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Vocalizations produced by bottlenose dolphins (Tursiops truncatus) during mouth actions in aggressive and non-aggressive contexts

Dolphins exchange information with conspecifics using different types of vocalizations that are often associated with specific behaviors. The present study used simultaneous acoustic and video recordings of captive bottlenose dolphins ( Tursiops truncatus ) in Honduras to describe potential correlations between the type of mouthing behavior (open mouth, mouthing, bite) and associated vocalizations (whistle, whistle-squawk, chirp, moan, burst-pulse ‘A’, burst-pulse ‘B’, clicks). Literature on sound-behavior relationships among odontocetes with the noted infrequent systematic analyses of mouth actions highlights the need for this investigation. The influence of aggression on vocalization use was also addressed. From this observational study a series of general expectations on the interaction of sound, mouth action, and aggressive context are presented. Mouth actions are associated with vocalizations more often than not, and results suggest an overall flexible association of vocalizations during mouth actions, with the production of various sounds altered during aggressive contexts. There is an apparent distinction of frequency-modulated sounds with mouthing, suggesting that frequency parameters are an important characteristic of information exchange during mouth actions, and further that mouth actions are individually distinct behaviors. A dichotomy of burst pulse sounds in association with aggressive and non-aggressive contexts also introduces the need to analyze pulsed sounds according to inter-pulse interval. This paper proposes that there may be an interactive function to the use of vocalizations during mouth actions that is not yet understood.


Elephant conservation: Reviewing the need and potential impact of cognition-based education

Conservation education programs centered on animal cognition seem to be effective in bringing humans closer to non-human species and thereby, influencing their conservation attitudes. Systematic evaluation of the impact of cognition-based education programs on the attitudes of participants has revealed positive feedback and an appreciation towards the species of interest. However, such evaluations are rare for species like elephants, who suffer severe conservation challenges such as high degrees of conflict with the local community. In this paper, we review the need for cognition-based education programs in elephant conservation as well as the need to evaluate these programs to assess their impact on conservation attitudes. In particular, we emphasize the need for such programs in the native ranges of elephants, which are more prone to human-elephant conflict, and argue that exposure to such programs may potentially increase the collaboration of the local community towards conservation efforts.

Seasonal, Diel, and Age Differences in Activity Budgets of a Group of Bottlenose Dolphins (Tursiops truncatus) Under Professional Care

Wild bottlenose dolphin ( Tursiops truncatus ) behavior is impacted by a number of factors including season, time of day, and age.  However, less is known about how these factors may influence animals under professional care in zoos, aquariums and marine parks. Management practices such as scheduled feeding times, human interactions, lack of predators and show performances may also impact the activity budgets of dolphins.  The current study examined the rest, swim and play behavior of seven dolphins (three adults, four calves) at one facility. Data were collected over the entire 24-hour day for a period of one year. Observed behaviors were recorded in mutually exclusive categories including rest, low intensity swim, high intensity swim, low intensity play, high intensity play and social play. Data were analyzed to determine how often dolphins engaged in particular behaviors and if activity budgets varied due to season, time of day and age.  These dolphins spent the majority of their time in low intensity swim and low intensity play.  The activity budget varied between observational periods.  First, seasonal differences were found in low intensity swim, low intensity play, social play and high intensity play behaviors.  In the comparison for time of day, differences were found in rest, low intensity swim, low intensity play and social play.  Finally, no significant differences were found in age comparisons. Information gained from this study can help to better understand how different factors influence the behavior of bottlenose dolphins under professional care within zoos, aquariums and marine parks.

Observations of a Paternal Male with Bottlenose Dolphin Calf (Tursiops truncatus): A Case Study

The rearing and socialization of bottlenose dolphin calves has been largely described as a female role, whether via direct maternal care or allomaternal parenting. Nevertheless, male associations have been observed but are rarely systematically investigated. This case study focused on the opportunistic occurrence of a single bottlenose calf and her associations with the mother, father and two unrelated allomothers in a captive setting. Observations were made postpartum of an adult male and his female calf multiple times per day over the course of the first year of the calf’s life, including social (proximity and orientation), aggressive (tail slapping/swatting, threats, jaw popping, chasing) and tactile behaviors. For comparative analyses, data were simultaneously collected on mother-calf and allomother interactions. The results revealed that cohabitation of the paternal male and offspring was prosocial, with negligible levels of aggression (0.03%) even during maternal estrous. The male demonstrated minimal aggressive behaviors toward the calf (e.g., chasing), none of which resulted in injury. Rather, the male’s interactions with the calf were considerably affiliative. Although the frequency of interactions between the paternal male and the calf were less than the mother’s, father-calf interactions were significantly more frequent than were calf interactions with other dolphins. Over the course of the study, the number of interactions the calf had with mother, father, and allomothers decreased. Overall, these results confirm that care can involve the paternal male, although the relative size of the enclosed setting limits extrapolations to the wild. Nonetheless, these observations suggest that some dolphin fathers may play a role in their calves’ social development and rearing.  Although additional research on calf socialization is required, the dolphin father in this study established and maintained a social bond with his female calf that was clearly affiliative, and these associations occurred significantly more often than those between the calf and her allomothers.


The preference for utilizing certain appendages (handedness) has been explored in human and nonhuman primates. Similarly to primates, dolphins possess hemispheres that allow an individual to present behaviorally dominant features as well as appendages (i.e., pectoral fins) that are utilized both as social facilitators as well as means to interact with objects. Thus, the possibility of handedness in a captive population of 27 bottlenose dolphins ( Tursiops truncatus ) was explored. Dolphins in a mother-offspring relationship made significantly more pectoral fin contacts than in the absence of this relationship ( p < 0.001). No significant difference was observed between maternal siblings and non-maternal siblings in overall pectoral fin contact. Handedness indexes were calculated for 26 individuals that initiated pectoral fin contact with both conspecifics and flora (i.e., seagrass) in their habitat. No significant differences were observed between the sexes in handedness indexes, however calves displayed a significant right-fin handedness compared to both sub-adults and adults ( p < 0.05). Both sub-adults and adults showed a left-fin handedness indexes, but no significant difference in the strength of this relationship among these two age classes was observed. Individual variation in handedness indexes was noted. These results suggest that handedness may be present in Atlantic bottlenose dolphins with regards to social contact, and a larger and more diverse sample size may provide a better understanding in why handedness may change across development.

Do Belugas (Delphinapterus leucas), Bottlenose Dolphins (Tursiops truncatus), & Pacific White-Sided Dolphins (Lagenorhynchus obliquidens) Display Lateralized Processing when Presented with Familiar or Novel Objects?

Lateralization of behaviors and information processing are common across species. Hypothesized to be crucial for more efficient responding to environmental stimuli, lateralization has been investigated for a number of topics. Cetaceans are proposed to be hemispheric specialists, given a small corpus callosum, complete decussation of the optic nerve, and the ability to respond to a different visual stimulus presented to each eye simultaneously. Research with cetaceans has shown strong biases in a number of behaviors, including swimming, foraging, social interactions, and responses to myriad visual stimuli. Given similar evolutionary pressures, different species of cetaceans should display similar lateralized preferences. Previous research with bottlenose dolphins in managed care and wild striped dolphins indicated a right eye preference when viewing unfamiliar objects. The purpose of the current study was to evaluate the eye preference of belugas, bottlenose dolphins, and Pacific white-sided dolphins (lags) in managed care when viewing familiar and unfamiliar objects. The results from 11 belugas, 5 bottlenose dolphins, and 5 lags indicated that consistent group level eye preferences were not present. The belugas preferred to view both types of objects with both eyes, with the majority of the belugas showing a left-eye preference when a monocular gaze was used. Bottlenose dolphins tended to view both objects with their right eye while lags used their left eye when viewing objects. These results may have been affected by viewing objects below water versus above water. The belugas and the Pacific white-sided dolphins were able to view the objects below water, which may have elicited more naturalistic visual examinations of the objects (i.e., greater ecological validity). Viewing objects within one’s habitat may facilitate the discrimination of an object rather than simply its detection, which is may be more likely when encountering stimuli above the surface of the water as the bottlenose dolphins had to do in the present and past research. Future research should compare if presentation of the stimulus above water versus below water affects the eye preference displayed.

Special Issue on Categorization: Causes and Consequences

Moving from perceptual to functional categories in songbirds

Category perception, as Herrnstein (1990) defined it, is a powerful and pervasive cognitive ability possessed by every species in which it has been adequately tested. We have studied category perception of vocal communication signals in songbirds for over 20 years. Our first studies provided us with an understanding of songbird vocal category production and perception, clarifying perceptual categorization and the underlying mechanisms. More recent work has moved towards understanding functional vocal categories such as sex, dominance, species, and geography. Some of our most recent work has moved into the realm of conceptual knowledge, with studies aimed at understanding birds’ ability to deal with concepts of sameness and danger (i.e., threat level). Here we provide key examples that effectively show the wide range of abilities possessed and used by songbirds.

Call Usage Learning by a Beluga (Delphinapterus leucas) in a Categorical Matching Task

The ability to modify the structure and context of vocalizations through learning plays a key role in the social interactions of many species.  The investigation of categorical matching, an aspect of contextual vocal learning, is the first step toward determining how contextual learning plays a role in the use, comprehension, and categorization of sounds in the wild.  To this end, we conducted a study at the Vancouver Aquarium to test the ability of a juvenile female beluga, Qila, to respond to playbacks of two types of in-air beluga calls with vocalizations that matched the category of call played (a scream, which is a vocalization type shaped over time with reinforcement and not part of this species'natural repertoire, and a pulse-train, a natural call category).  We first tested Qila with random sequences of the same version of the two vocalizations with which she had been trained.  Her overall success in matching all playback stimuli was above chance but not statistically so (66%).  She had more difficulty matching screams (54% success) than pulse trains (80% success).  We next played random sequences of six novel pulse-trains and seven novel screams, which Qila had not been trained with.  She responded correctly to the set of novel stimuli of both call types in 64% of the trials, a success rate that did not differ statistically from chance.  Again, she had more difficulty matching screams (55% success), relative to pulse trains (74% success).  These results indicate that Qila successfully matched only pulse trains, the class that is part of this species’ natural repertoire.  Her poor performance on matching screams might be partly explained by a difficulty to perceive categorically a signal that lacks a function in the natural repertoire of belugas.

Keywords: categorical matching, contextual learning, vocal learning, categorization, belugas

Categorization of Emotional Facial Expressions in Humans with a History of Non-suicidal Self-injury

In social animals, such as humans, accurate emotion expression categorization is important for appropriate social functioning. Inaccuracy in emotion categorization can lead to inadequate social behavior, commonly seen in various psychiatric disorders. Non-suicidal self-injury (NSSI) is a psychiatric symptom involving deliberate self-inflicted injury of one’s body, without intent to die. NSSI has been regarded as a dysfunctional coping strategy for managing intensely difficult feelings. Difficulties in social interactions have been reported by individuals who engage in NSSI, which may be related to their emotion categorization performance. Participants (17-25 yrs) with a history of NSSI and healthy controls viewed videos of faces changing over 10 s from neutral to a prototypical expression of sadness, disgust, surprise, fear, anger or happiness. They were instructed to stop each video as soon as they felt they recognized the emotion presented, thus indicating the minimum intensity of expression needed for categorization. They were then asked to categorize the expression. Minimum facial expression intensity, accuracy of categorization, and reaction time were the behavioral dependent variables of interest. NSSI participants showed significant advantages compared to controls in their ability to categorize negative emotion expressions, specifically fear, anger, disgust, and sadness. They also were able to recognize the ambiguous emotion of surprise at a lower stimulus intensity. To date, treatments for NSSI have high drop-out rates. Results from this research could be used to inform further development of therapies for the alleviation or prevention of NSSI.


Carnivore concepts: Categorization in carnivores “bears” further study

Although categorization abilities may serve as the foundation for most other complex cognitive processes, this topic has been grossly understudied in the order Carnivora. However, there are a growing number of studies examining the abilities of bears, felines, and canines to discriminate among stimuli that could represent conceptual categories. These studies are few in number compared to the extensive work conducted on non-human primates, but, thus far, results suggest that carnivores show comparable abilities to, for example; form natural categories, discriminate quantities, recognize cues of human emotion, and to discriminate kin. There is little existing work exploring concepts of sameness and relational reasoning in carnivores, and work on social concepts, such as representations of mental states, exist only in canines. Future studies are necessary to better understand the mechanisms underlying carnivores’ categorization abilities and conceptual representations. Furthermore, future work should focus on differences in conceptual ability as a function of social lifestyle and dietary preferences within carnivores. Such studies will be helpful in understanding the evolutionary pressures responsible for conceptual processes in a variety of species, including humans.

Can Dogs Learn Concepts the Same Way We Do? Concept Formation in a German Shepherd

Growing evidence shows that dogs can complete complex behavioral tasks, such as learning labels for hundreds of objects, readily learning the name of a novel object, and responding differentially to objects by category (e.g., “toy,” “ball,” “Frisbee”). We expand here on the evidence for complex behavioral abilities in dogs by demonstrating that they are capable of concept formation by strict criteria. A German shepherd responded differentially to two sets of objects (“toys” and “non-toys”) in Experiment 1. Additionally, the dog’s differential responding in Experiment 1 occurred from the first trial, indicating that he entered the experiment with this stimulus class already differentiated from his day-to-day exposure to contingencies. In Experiment 2 we used a common response (tug-of-war) with three objects that were not retrieved in Experiment 1 to attempt to add these objects to the stimulus class. After repeated sessions of tug-of-war, the dog began retrieving all three objects in the retrieval test, although the rates of retrieval varied between objects. Finally, in Experiment 3, we conducted a transfer of function test in which the dog emitted a new response to untrained exemplars suggesting that his differential responding in Experiment 1 was indicative of a concept by the strictest criteria. Additionally, he reliably emitted the new response in the transfer test to one of the three new objects from Experiment 2, suggesting this object had been reliably added to the conceptual class.


A transferrable change in preferences of floral patterns by bumblebees through reward reversal

This study examines the use behavioral transfer across perceptually similar stimuli in bumblebees ( Bombus impatiens ) and addresses whether foraging judgments about a floral stimulus can change in a way that contradicts direct previous experience with that stimulus. Twenty bees from each of four colonies underwent discrimination training of stimuli placed in a radial maze. Bees were trained to discriminate between two corresponding object and photograph pairs of artificial flowers, where one object and its corresponding photo were rewarding, while another object and its corresponding photo were unrewarding. Following discrimination training, one stimulus from each pair (either the object or the photo) was removed. The predictive reward values of the remaining stimuli were either switched for one group or stayed the same for another. Subsequent testing on the removed stimuli revealed foraging preferences to shift based on experience with the other stimulus in the group. For instance, bees treated a previously unrewarding object as rewarding after learning that the corresponding photograph had become rewarding. Foraging decisions depend not only on previous experience with stimuli, but also category membership.

Relation between Exclusion and Stimulus Equivalence Class Formation in Auditory-visual and Visual-visual Matching in Preschoolers

The hypothesis that exclusion performance is a prerequisite for the stimulus equivalence class formation was assessed in preschoolers of about 5 years of age. In Experiment 1, two groups of children were trained in a set of conditional discriminations in a two-choice matching to sample format, Group 1 in an auditory-visual modality baseline, and Group 2 in a visual-visual modality baseline. Exclusion test trials included an undefined (not previously related) comparison stimulus, and a defined (i.e., related in the baseline) comparison stimulus, in the presence of an undefined sample stimulus. Selection of the undefined comparison was recorded as a correct response. Stimulus equivalence class formation was assessed by way of symmetry and transitivity test trials. Experiment 2 replicated the design of the first experiment, with the difference that exclusion was assessed independently and with a different baseline from symmetry and transitivity. Exclusion scores were higher for the auditory-visual groups than the visual-visual groups. In both modalities symmetry scores were superior to those in transitivity.  Symmetry showed independent from the exclusion performance, but transitivity was presumably dependent from it in the auditory-visual modality.


Songbirds as objective listeners: Zebra finches (Taeniopygia guttata) can discriminate infant-directed song and speech in two languages

Despite their acoustic similarities, human infants are able to discriminate between infant-directed song (as produced by human adults) and infant-directed speech in both English and Russian. However, experimenters are somewhat limited in what they can test using the preference paradigm with infants. As a complement to a previous infant study (Tsang et al. 2016), we asked whether a songbird, the zebra finch, could discriminate infant directed song and speech in English and Russian, and tested responses to stimuli that humans could not categorize as either type. Male and female zebra finches learned to discriminate the stimuli in both languages equally well, although females were slightly faster at learning the discrimination, and generalized responses to untrained stimuli of the same categories. Bird responses to stimuli that humans could not categorize likewise did not follow a clear pattern. Our results show that infant-directed song and speech are discriminable as categories by non-humans, that song and speech are as easy to discriminate in English and Russian, and that comparative studies together can provide more complete answers to research questions about auditory perception and acoustic features used for discrimination than using one species or one language alone.

  • 6 supplemental audio files

How and Why Does Category Learning Cause Categorical Perception?

Learning to categorize requires distinguishing category members from non-members by detecting the features that covary with membership. Human subjects were trained to sort visual textures into two categories by trial and error with corrective feedback. Difficulty levels were increased by decreasing the proportion of covariant features. Pairwise similarity judgments were tested before and after category learning.  Three effects were observed: (1) The lower the proportion of covariant features, the more trials it took to learn the category and the fewer the subjects who succeeded in learning it. After training, (2) perceived pairwise distance increased between categories and, to a lesser extent, (3) decreased within categories, at all levels of difficulty, but only for successful learners. This perceived between-category separation and within-category compression is called categorical perception (CP). A very simple neural network model for category learning using uniform binary (0/1) features showed similar CP effects. CP may occur because learning to selectively detect covariant features and ignore non-covariant features reduces the dimensionality of perceived similarity space. In addition to (1) – (3), the nets showed (4) a strong negative correlation between the proportion of covariant features and the size of the CP effect. This correlation was not evident in the human subjects, probably because, unlike the formal binary features of the input to the nets, which were all uniform, the visual features of the human inputs varied in difficulty.

  • 1 supplemental ZIP

Brief Report

Yawn duration predicts brain volumes in wild cats (Felidae)

Recently, yawn duration was shown to be a robust predictor of brain size and complexity across a diverse sample of mammalian species. In particular, mammals with larger brains and more cortical neurons have longer yawns on average. Here, we investigated whether this relationship between yawn duration and brain size, which was previously at the taxonomic rank of class, is also present within a more restricted scale: a family of mammals. Using previously published data on brain weight and endocranial volumes among various field species within the family Felidae, we ran correlations with yawn durations obtained from openly accessible videos on the Internet. Consistent with previous findings, we show a strong linear relationship between yawn duration and both brain weight and brain volumes among wild cats. However, yawn duration was not significantly correlated with species body weight. Although limited to a small sample, these results provide convergent evidence for an important and general neurophysiologic function to yawning and highlight the utility of measuring yawn duration in comparative research.