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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 31, 2018

Special Issue: Tribute to Dr. Duane Rumbaugh

Research Article

Characterizing curiosity-related behavior in bottlenose (Tursiops truncatus) and rough-toothed (Steno bredanensis) dolphins

Dolphins are frequently described as curious animals; however, there have been few systematic investigations of how dolphins behave when they are curious and the extent to which individual differences in curiosity exist in dolphins. Previous research has described individual differences in dolphins’ frequency of interactions with environmental enrichment as well as quantifying curiosity-related traits of dolphins via personality assessments, though behavioral observation and trait rating components have not been part of the same study. The present study describes two different experiments designed to elicit curiosity in 15 bottlenose ( Tursiops truncatus ) and 6 rough-toothed ( Steno bredanensis ) dolphins. In Experiment 1, dolphins displayed more curiosity-related behavior toward a stimulus with spontaneous movement (jack-in-the box) compared to their reaction to a static control object; however, in Experiment 2, the subjects did not conform to hypotheses, and displayed few behavioral differences when shown expectation-violating stimuli compared to a control stimulus. The results of this study supported the hypothesis that there would be a wide range of individual differences in dolphins’ reactions to the stimuli, including differences between species and sex, as well as differences in trait ratings by trainers. These findings provide information that may be useful for future research aimed at assessing curiosity in dolphins, as well as for making environmental enrichment decisions for dolphins in human care.

The progressive elimination task in dogs (Canis familiaris): The case of divergence

Domestic dogs (Canis familiaris) were administered progressive elimination tasks in which they had to visit and deplete either 3 or 4 baited sites. They were brought back to the starting point after each visit.  When administered a 4-choice task with small angular deviation between adjacent targets, the dogs chose first an inner target (e.g., right inner target) and the opposite outer target (e.g., the left target) as a second correct choice.  So they relied on divergence; that is they chose the farthest target as the next choice.  Varying angular deviation did not modulate divergence.  Decreasing the number of targets (3-choice task, Experiment 2) did relax divergence, though target selection was not totally random.  The dogs still chose as a first choice an inner target (i.e., the middle target) when selecting the most divergent patterns of elimination. Finally, in Experiment 3, the dogs were administered a 3-choice task with large angular deviation but in which all targets had been hidden.  The dogs chose first an outer target (i.e., right or left)) and the other outer target as the second correct choice.  That is they relied on divergence.  The results suggest that divergence is the outcome of a flexibility/cognitive load tradeoff when facing novelty and uncertainty.

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Spontaneous preference for primate photographs in Sumatran orangutans (Pongo abelii)

Spontaneous looking preferences were assessed in six zoo-housed orangutans. Orangutans were presented with two photographs simultaneously on two identical laptop computers. Preference was measured by calculating the relative looking time for photographs from each stimulus category, over three studies. Orangutans exhibited moderate interest in looking at photographs, with four orangutans participating in Study 1 and Study 2, and six orangutans participating in Study 3. The results of Study 1 showed that orangutans preferred photographs of unfamiliar orangutans over unfamiliar humans. Study 2 results showed that orangutans preferred photographs of familiar orangutans over unfamiliar orangutans. In Study 3, preferences were assessed using photographs of the nine members of the participants’ own orangutan social group. Orangutans preferred photographs of adults over infants, and males over females. Similar studies have reported varied preferences, and we propose that variation is a result of complex demographic and social factors.

Extinction of running-based taste aversion in rats (Rattus norvegicus)

Wheel running establishes conditioned aversion in rats to a taste solution consumed shortly prior to the running. Many studies have shown that this is a case of Pavlovian conditioning, in which the taste and running respectively act as the conditioned stimulus (CS) and the unconditioned stimulus (US), but extinction of this running-based taste aversion has not been explicitly demonstrated. Experiment 1, using a within-subjects design, showed that saccharin aversion formerly established by a single pairing of an exposure to saccharin solution with a running opportunity was extinguished by two daily exposures to the saccharin solution. However, there was no spontaneous recovery from extinction in the tests which were administered 6 and 27 days after the extinction days. Experiment 2, using a between-groups design, successfully demonstrated extinction and spontaneous recovery of running-based saccharin aversion, when rats were treated with a paradigm of 8 conditioning days, 8 extinction days, and 8 retention days.

Discrimination of food amounts by the domestic dog (Canis familiaris) - A small sample study

The current research examined dog's ability to dsicriminate between different amounts of food. Using a two alternative forced choice procedure dogs werre required to discriminate between a constant amount of 4 pieces of food and another amount that varied across a range from 1 to 7 pieces. The dogs reliably selected the larger of two alternatives. Discrimination was better when there were fewer rather than more than 4 pieces of food available on the varying alternative. Specifically, 1 was discriminated from 4 more easily than 4 was discriminated from 7 pieces of food. These results confirmed the ability of dogs to discriminate food amount on a psychophyical choice procedure.

Effects of temporal and spatial allocation of water delivery on water-seeking behavior in rats

We evaluated the effects of varying temporal and spatial parameters on behavioral transitions within a water seeking situation. Subjects were 8 experimentally-naïve, male Wistar rats divided in two groups of 4 rats. For both groups, two independent schedules of water delivery were simultaneously available in two different locations of the experimental chamber. For Group 1, water was delivered with a constant periodicity. For Group 2 water was delivered randomly in time but keeping constant the average length of time between deliveries. Water deliveries were independent of rat’s behavior. In successive phases of the study, the frequency of water delivered in one location increased while the frequency of water delivered in the second location decreased, keeping constant the total number of water deliveries. Rats under the constant periodicity spent more time in the location where water was initially provided. For rats under the random periodicity, time spent on each location varied according to the proportion of water delivered on each site. Results are discussed in terms of the discrepancies with optimization models, emphasizing that, apparently simple behaviors, in a relatively simple environment, cannot be understood in terms of a single, overall encompassing concept, such as adaptation.


Robots Can Train Humans Using Principles of Operant Conditioning Through Visual Reinforcement Tools

Researchers have established new techniques to study human-robot interactions based on current knowledge in interspecies communication and comparative psychology.  Studies on animal acceptance of robot conspecifics in complex social environments has led to the development of robots that adapt to animal and human behaviors.  Using a robot with adaptable algorithms developed by the authors, the researchers hypothesized that, by using familiar visual rewards as positive reinforcement, robots could use operant conditioning principles to teach humans a basic task. The robot in this study independently determines optimal control of construction equipment by capturing the motions from an expert operator.  The robot then attempts to teach those same skills to novice operators using familiar, yet simple, visual reinforcement tools. In this study, participants were asked to manipulate a model excavator using feedback from the guidance system on a nearby computer screen.  Participants were randomly assigned to one of three groups: simple visual reinforcement, complex guidance, and no visual feedback (blank screen).  To measure learning, participants returned a day later to repeat the task without the guidance.  The group using simple feedback resulted in cycle times that were closer to the expert times than both the complex or control groups and were significantly different end times (p < .05) than either group.    This result supports our hypothesis that, similar to what’s been found in vertebrates and invertebrates, robots can shape behaviors of humans using visual positive reinforcement.

Special Issue on Contact

Expanding Perception: The Role of Touch in Comparative Psychology; Introduction to the Special Issue

In recent years, researchers have begun to include diverse modes of perception in comparative studies, such as vocal and tactile forms of communication, in an effort to understand social, cognitive, and affective processes in various species. In this special issue, we have collected a series of articles that approach from an interdisciplinary perspective (i.e., psychology, behavioral sciences, anthropology, and philosophy) how touch/contact has been included in diverse fields of research and exploring the new insights produced by including this mode of perception.

Infant Handling Among Primates

Primates, particularly females, tend to be attracted to infants that are not their own and are often highly motivated to touch and handle them. However, species vary markedly in forms of handling and extents to which handling constitutes direct care (e.g., carrying and nursing), other affiliative behaviors, or aggression/ abuse. Here we review infant handling among primates from ultimate and proximate perspectives, focusing on a promising, but understudied hypothesized benefit—that handling enhances social bonds. We pay special attention to macaques and baboons, because infant handling in most of these species poses a special challenge in that it involves little actual care, and hence may be shaped by different and as yet unclear selective pressures from typical alloparental care. Costs, benefits, and hypothesized functions appear to vary across species based on: a) individuals’ roles (mother, handler, and infant), b) each of their characteristics, c) relationships between handlers and mothers, and d) the social context within the group. As a result, observed patterns of handling appear to be complex outcomes of the interaction of different, sometimes conflicting interests. The most promising hypotheses based on short/ medium term benefits appear to vary with breeding system, reproductive biology, socioecological factors, and life history characteristics. Explanations based on life history variables or long-term evolutionary processes related to cooperation appear to have broader applications, but nevertheless fail to explain infant handling in all its manifestations. We end by calling for more quantitative comparative and longitudinal research to further elucidate our understanding of this puzzling behavior.

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Bringing Touch Back to the Study of Emotions in Human and Non-Human Primates: A Theoretical Exploration

This paper provides a theoretical exploration of how comparative research on the expression of emotions has traditionally focused on the visual mode and argues that, given the neurophysiological, developmental, and behavioral evidence that links touch with social interactions, focusing on touch can become an ideal mode to understand the communication of emotions in human and non-human primates. This evidence shows that touch is intrinsically linked with social cognition because it motivates human and non-human animals, from birth, to form social bonds. It will be shown that touch is one of the modes of interaction used by the mother-infant or caregiver-infant dyad that facilitates the expression of emotions by the infant (and later the expression of emotions by the adult that the infant has become) in ways that are understood by other members of the group.


The functions of mutual touch in full-term and very low-birthweight/preterm infant-mother dyads: Associations with infant affect and emotional availability during face-to-face interactions

The purpose of the present study was to investigate the communicative functions of mutual touch during mother-infant interactions and their relation with infants’ affect and the quality of the mother-infant relationship. The two normal periods of the Still-Face procedure were examined for mothers and their 5½-month-old full-term (n=40) and very low-birthweight/preterm (VLBW/preterm; n=40) infants. The Functions of Mother-Infant Mutual Touch Scale was used to code the function of each mutual touch. Results indicated that full-term infant-mother dyads spent significantly more time engaged in playful and regulatory mutual touch compared to VLBW/preterm infant-mother dyads who spent significantly more time engaged in attention-centered, unbalanced, and guided mutual touch. Infant smiling was found to significantly co-occur with playful mutual touch for both the full-term and VLBW/preterm infants, while fretting co-occurred with unbalanced mutual touch for VLBW/preterm infants. Higher levels of maternal sensitivity and regulatory mutual touch were associated for full-term dyads, while lower levels of maternal sensitivity were associated with unbalanced mutual touch for VLBW/preterm dyads. Results from this study enable a more comprehensive understanding of the functions of mutual touching, and suggest key differences in which mutual touching behaviours are organized with infants’ affect and relationship dimensions between mothers and their infants.

Hearing Parents’ Use of Auditory, Visual, and Tactile Cues as a Function of Child Hearing Status

Parent-child dyads in which the child is deaf but the parent is hearing present a unique opportunity to examine parents’ use of non-auditory cues, particularly vision and touch, to establish communicative intent. This study examines the multimodal communication patterns of hearing parents during a free play task with their hearing (N=9) or deaf (N=9) children. Specifically, we coded parents’ use of multimodal cues in the service of establishing joint attention with their children. Dyad types were compared for overall use of multimodal – auditory, visual, and tactile – attention-establishing cues, and for the overall number of successful and failed bids by a parent for a child’s attention. The relationship between multimodal behaviors on the part of the parent were tracked for whether they resulted in successful or failed initiation of joint attention. We focus our interpretation of the results on how hearing parents differentially accommodate their hearing and deaf children to engage them in joint attention. Findings can inform the development of recommendations for hearing parents of deaf children who are candidates for cochlear implantation regarding communication strategies to use prior to a child’s implantation. Moreover, these findings expand our understanding of how joint attention is established between parents and their preverbal children, regardless of children’s hearing status.

The role of physical activity and touch in children’s social bonding

Physical activity (PA) and touch, long known to facilitate interpersonal affiliation in adults and non-human primates, are common elements of children’s free play. However, no research has examined how children’s play involving PA and touch is linked with social bonding (i.e., positive emotional states and behaviors that help create, maintain and characterize affiliation and attachment among individuals). This paper reports on two novel studies designed to explore these links in children’s play. In two studies, we investigated associations between PA, touch and prosociality in 5-to-8-year-old children. In a naturalistic observation study ( N = 50), we assessed the amount of PA, smiling/laughing, touch, and prosociality in children’s play behavior during school breaks. PA levels were also measured indirectly via heart rate monitors (HRM). The findings revealed that observed-PA was associated with the amount of smiling/laughing. PA (observed and HRM) was also associated with the amount of touch. In a second study ( N = 84), we experimentally tested the effect of touch on helping behavior in the context of physically-active play. In pairs, children ran to collect felt shapes which they placed either onto each other (touch condition) or onto a board (no-touch condition). Subsequent helping behavior was assessed in a separate task. There was a non-significant trend towards more helping in the touch condition. We discuss the findings in terms of the significance of PA and touch for social bonding in childhood and offer suggestions for future research in this underexplored area.


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The Tactile Senses of Marine Mammals


The successful return of mammals to aquatic environments presented numerous sensory challenges to overcome.  Aquatic habitats reduced the utility of vision and the type of chemoreception important in terrestrial perception. In several orders, the sense of touch assumed greater importance, especially when enhanced by the development of vibrissal (sensory hair) systems.  Species of two extant orders, Sirenia and Cetacea, lost all of their hairs except for vibrissae. In the former, these hairs cover the entire bodies of the two families, Trichechidae and Dugongidae.  Hairs in adult cetaceans are more constrained (e.g., some river dolphins and baleen whales) and are restricted primarily to rostral regions.  Pinnipeds and sea otters retained their pelage, but in addition have elaborated their mystacial and other facial vibrissae.  High numbers of vibrissal receptors, associated dense innervation, prominence of neural tracts, and hypertrophy of brain areas associated with touch suggest an importance of tactile senses for aquatic mammals.  Experimental testing has demonstrated the exquisite tactile sensitivity of many marine mammal species. Sensory hairs contribute to that tactile sensitivity in both haptic and mechanosensory contexts.  Several, if not most, pinniped species, seals and sea lions, can track prey based on mechanoreception alone.  In this review we will discuss the neurobiological and behavioral evidence for the tactile senses of marine mammals.

Duane Rumbaugh Special Issue

Duane M. Rumbaugh (1929-2017), Comparative Psychologist: Introduction to the Special Issue

This special issue is dedicated to Dr. Duane Rumbaugh.  Leaving a lasting legacy in the field of comparative psychology, Dr. Rumbaugh helped to pave the way for cognitive and behavioral research with primates.  This special issue is comprised of a set of papers that both commerate and illuminate his contributions. Written by former students and colleagues, this collection of papers highlights his substantial influence on the development of primatology.

Duane M. Rumbaugh: Some Biography and Early Research

Information about Duane M. Rumbaugh’s family, education, and career is presented in the first section. In a second section, information about Rumbaugh’s publications from 1962 to 2015 is presented, and details about his early research publications are provided. Although a few of his early publications involved applied research with humans, most of his early programmatic research involved various non-human primates, modifications of research equipment, and development of new measures of learning sets. Implications of the early research for later research also are discussed.

Does Joystick Training Facilitate Relational Learning?

Thirteen naïve capuchin monkeys ( Cebus [Sapajus] apella ) were manually tested with the Transfer Index procedure, a species-fair paradigm for assessing the capacity to learn and to transfer learning. The animals were then trained to manipulate a joystick to control a cursor and to respond to stimuli on a computer screen. After the animals had mastered the remote cause-effect relations required by the computerized test system, they were returned to manual Transfer Index testing to determine whether the joystick-training intervention had affected the monkeys’ capacity for efficient and relational learning.  Transfer Index scores and overall accuracy was higher following the joystick intervention, but these differences were not statistically significant. Two-choice discrimination learning and reversal appeared to be associative in nature, and there was no evidence that joystick training made the monkeys more rule-like or relational in their learning. Despite the absence of significant differences, the patterns of results encourage further study of the ways that changes in the cognitive competencies of nonhuman animals might be catalyzed by significant learning experiences.

Responses to modified Monty Hall Dilemmas in capuchin monkeys, rhesus macaques, and humans

The Monty Hall Dilemma (MHD) is a simple probability puzzle famous for its counterintuitive solution. Participants initially choose among three doors, one of which conceals a prize. A different door is opened and shown not to contain the prize. Participants are then asked whether they would like to stay with their original choice or switch to the other remaining door. Although switching doubles the chances of winning, people overwhelmingly choose to stay with their original choice. To assess how experience and the chance of winning affect decisions in the MHD, we used a comparative approach to test 264 college students, 24 capuchin monkeys, and 7 rhesus macaques on a nonverbal, computerized version of the game. Participants repeatedly experienced the outcome of their choices and we varied the chance of winning by changing the number of doors (three or eight). All species quickly and consistently switched doors, especially in the eight-door condition. After the computer task, we presented humans with the classic text version of the MHD to test whether they would generalize the successful switch strategy from the computer task. Instead, participants showed their characteristic tendency to stick with their pick, regardless of the number of doors. This disconnect between strategies in the classic version and a repeated nonverbal task with the same underlying probabilities may arise because they evoke different decision-making processes, such as explicit reasoning versus implicit learning.

Assessing Distinctiveness Effects and “False Memories” in Chimpanzees (Pan troglodytes)

There are many parallels between human and nonhuman animal cognitive abilities, suggesting an evolutionary basis for many forms of cognition, including memory. For instance, past research found that two chimpanzees exhibited an isolation effect, or improved memory for semantically distinctive items on a list (Beran, 2011). These results support the notion that chimpanzees are capable of semantic, relational processing in memory, and introduce the possibility that other effects observed in humans, such as distinctiveness effects or false memories, may be present in nonhuman species. The Deese-Roediger-McDermott (DRM) paradigm is a commonly used task to explore these phenomena, and it was adapted for use with chimpanzees. We tested four chimpanzees for isolation effects during encoding, distinctiveness effects during recognition, and potential “false memories” generated by the DRM paradigm by presenting a serial recognition memory task. The isolation effect previously reported (Beran, 2011) was not replicated in this experiment. Two of four chimpanzees showed improved recognition performance when information about distinctiveness could be used to exclude incorrect responses. None of the chimpanzees were significantly impaired in the “false memory” condition. However, limitations to this approach are discussed that require caution about assuming identical memory processes in these chimpanzees and in humans.

A Chimpanzee’s (Pan troglodytes) Perception of Variations in Speech: Identification of Familiar Words when Whispered and When Spoken by a Variety of Talkers

When humans perceive speech they process the acoustic properties of the sounds. The acoustics of a specific word can be different depending on who produces it and how they produce it. For example, a whispered word has different acoustic properties than a word spoken in a more natural manner; basically, the acoustics are “noisier.” A word will also sound differently depending on who speaks it, due to the different physical and physiological characteristics of the talker. In this instance, humans routinely normalize speech to retrieve the lexical meaning by solving what is termed the “lack of invariance” problem. We investigated these speech perception phenomena in a language-trained chimpanzee ( Pan troglodytes ) named Panzee to ascertain if more generalized auditory capabilities, as opposed to specialized human cognitive processes, were adequate to accomplish these perceptual tasks. In Experiment 1 we compared the chimpanzee’s performance when identifying words she was familiar with in natural versus whispered form. In Experiment 2 we investigated Panzee’s ability to solve the “lack of invariance” problem when familiar words were spoken by a variety of talkers (familiar and unfamiliar male and female adults, and children). The results of Experiment 1 demonstrated that there was no difference in her recognition for the two word types. The results of Experiment 2 revealed no significant difference in Panzee’s performance across all talker types. Her overall performance suggests that more generalized capabilities are sufficient for solving for uncertainty when processing the acoustics of speech, and instead favor a strong role of early experience.

The Fully Conscious Ape

Duane Rumbaugh was one of the first primatologists of the modern era (which began after WWII), to engage in comparative studies of the cognitive capacities of nonhuman primates.  In fact, it was Rumbaugh who drew the world's attention to the Order Primates and who helped initiate the International Primatological Society, IPS, the first academic society to be organized around an Order rather than a discipline. His work eventually led in two directions, first the development of the Transfer Index, a was completely new way of looking at learning. The TI seperated monkeys from apes as completely as did Gallup's mirror task.  From this arose the Primate Test Battery, a video based system to test cognitive skills across a wide range of tasks from memory to numerical skils in primates. The other direction was to look at language and its effect on cognition. Only Apes succeeded in the laguage tasks. With Lana's success arose a raft of critiques that - in the light of more recent findings about the structure of human language, are now rendered invalid. Rumbaugh's initial findings in all domains has remained sound. This includes fundamental differences between monkeys and apes in their capacity to spontaneously begin control their attention, to consciously monitor their own behavior, and then to alter it deliberately, or by their own choice. It is the ape's conscious capacity to control its attention and to conciously monitor outcomes in a cause/effect manner, that allows for the acquisition of langauge. This also allows for the creation of "personal self", as a being that exists apart from the current experience of the self. Language greatly assists the emergence of this ability in apes, as does early rearing in which the ape is carried but not seperated from its mother. This allows pointing and joint reference to appear far ahead of schedule and for the spontaneouls development of human  language in cross-species co-reared apes.  The presence of a wild-reared mother (not present in other captive environments)also allows for the emergence of a nonhuman form of vocal language. The implications of this work for future investigations of apes are discussed.

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Duane Rumbaugh’s Influence on the Science and Practice of Animal Welfare

Duane Rumbaugh’s influence on the field of comparative psychology will be long lasting and far reaching. He is best known for his continuing influence on the field of primate cognition, but his work and that of his mentees has branched out into other domains as well.  Here we will focus specifically on his influence on the field of animal welfare and how place or location has shaped those influences. In our narrative, we will describe how different people with different perspectives interfaced over the decades by virtue of sharing space. We will reflect on a range of physical spaces: field versus wild, different cities or geographical locations, laboratory versus zoo, and actual versus virtual. Geographic location, indirectly and/or directly, will shape the interactions among scientists and their perspectives and values. In particular we will focus on how developments in the 20 th Century in San Diego and Atlanta shaped the primate research community in both laboratories and zoos. We will provide the historical context and development of perspectives that have forever altered how we think of and co-exist with great apes. These interactions have yielded positive and strong connections between people that ultimately influence our understanding of and treatment of animal welfare.

The value of Duane Rumbaugh's "comparative perspective" ... in neurobiology

One commonality across the wide-ranging influences Duane Rumbaugh had on late-20 th century science was his commitment to the comparative perspective in psychology. I argue here that a commitment similar in force to Rumbaugh’s also infuses mainstream experimental neurobiology. This connection is ironic because Rumbaugh eschewed brain intervention experimentation in vivo throughout his scientific career. Still, the influence and value of a perspective similar to Rumbaugh’s can be found in neurobiology in at least three places. First, recent neurobiology has made good on one of Rumbaugh’s predictions, that rearing and early environment will be shown to influence behavior and cognition in nonprimate animals. Second, the epistemologically justified use of animal models in experimental neurobiology to investigate human brain mechanism presupposes a strong commitment to the comparative perspective. Third, commitment to the comparative perspective raises the most pressing ethical concern in neurobiology, namely, how is it ethical to perform brain intervention experiments on animal models if their brain mechanisms and behaviors compare closely enough with ours to justifiably generalize these experiments’ results?

Special Issue: Comparative Psychology Today

The State of Comparative Psychology Today: An Introduction to the Special Issue

Comparative psychology has long held an illustrious position in the pantheon of psychology. Depending on who you speak with, comparative psychology is as strong as ever or in deep decline. To try and get a handle on this the International Journal of Comparative Psychology has commissioned a special issue on the State of Comparative Psychology Today. Many of the articles in this issue were contributed by emanate comparative psychologists. The topics are wide ranging and include the importance of incorporating comparative psychology into the classroom, advances in automating, comparative cognition, philosophical perspectives surrounding comparative psychology, and issues related to comparative methodology. Of special interest is that the issue contains a listing of comparative psychological laboratories and a list of comparative psychologists who are willing to serve as professional mentors to students interested in comparative psychology. We hope that this issue can serve as a teaching resource for anyone interested in comparative psychology whether as part of a formal course in comparative psychology or as independent readings.The State of Comparative Psychology Today: An Introduction to the Special Issue

Let Us Bring Comparative Psychology Back

This article serves as the introduction to the special issue “The State of Comparative Psychology Today” for the International Journal of Comparative Psychology . Following opening comments, citations are provided in several areas all with the goal of stimulating students and professionals to help return comparative psychology to a prominent place in psychology. The material can be used as part of a reading list for a course in comparative psychology or as independent readings. It can also be used to shape a reasoned argument why comparative psychology should become a central part of a student’s training in psychology. Sections include books, citations on the history of comparative psychology, general issues related to comparative, teaching, and ancillary material such as websites, journals, videos and a free app for android phones that teaches students how to observe behavior.

More than a fluke: Lessons learned from a failure to replicate the false belief task in dolphins

Critical to advanced social intelligence is the ability to take into consideration the thoughts and feelings of others, a skill referred to as Theory of Mind (ToM) or mindreading.  In this article, we present a critical review of the comparative methodology and utility of the nonverbal FBT along with a description of an attempted FBT replication conducted with a bottlenose dolphin prior to the implementation of the more successful approaches used currently. Attempting to replicate Tschudin’s (2001, 2006) methodology with dolphins highlighted several flaws that may explain the failures of socially complex mammals to display competency: (1) reliance on a containment invisible displacement procedure that is difficult for non-human animals and especially dolphins to follow, (2) a complex procedure which demands extensive training time, (3) a long trial duration with several moving parts which taxes the animal’s memory and attention, and (4) a restricted number of two-choice FBT test trials, which limits statistical power given the small pool of trained animals. Although recent research paradigms for primates have corrected for some of these flaws, it is critical that comparative psychologists address these limitations for other species or taxa to be tested validly.  Future research in ToM understanding through a false belief approach should move toward more ecologically valid designs and appropriate implicit measures that facilitate comparative approaches that can be replicated.

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The Importance of a Truly Comparative Methodology for Comparative Psychology

Comparative research has taught us much about the evolution and development of human and animal behavior. Humans share not just physical and biological similarities with other species, but also many behavioral traits and, in some of these cases, the psychological mechanisms behind them. Comparing behavior and cognition across multiple species can help scientists to pinpoint why and when in phylogenetic history a behavior may have evolved, how it evolved, and what the mechanisms behind it are (Tinbergen, 1963). While the comparative approach has proven quite effective in addressing these questions, comparing behavior across multiple species is not as easy and straightforward as it may initially seem. Rigorous methodology and careful interpretation of results is crucial to answering any of these questions definitively. The focus of the current article is on the comparative methodology and the important factors that need to be addressed in order for comparative research to be effective. We first discuss the benefits and importance of comparative research, followed by the challenges that need to be overcome in good comparative work. We then discuss experimental economics as one “model system” for comparative work that has proven particularly good at addressing such issues, and comment on other approaches. We conclude with future directions for comparative research with an eye on important methodological and theoretical considerations.

Bottoms-up! Rejecting Top-down Human-centered Approaches in Comparative Psychology

Although comparative psychologists have made considerable strides in the past several decades, expanding the breadth of species and questions examined, the field still suffers from an overemphasis on top-down approaches that begin and end with a focus on humans. This top-down perspective leads to biases and oversights that hamper the further development of the field. A bottom-up approach that considers species-specific abilities and behaviors in the context of theoretically relevant comparisons will be most useful in advancing knowledge of species-specific and shared abilities. This will allow a better determination of the extent to which continuities and discontinuities exist as a function of different ecological forces. In addition, a bottom-up approach will facilitate a shift in focus from using animals to better understand humans, to understanding animals themselves. This new approach will allow for an appreciation of how humans can benefit other species.

Ordinal pattern analysis in comparative psychology - A flexible alternative to null hypothesis significance testing using an observation oriented modeling paradigm

The data of comparative psychology generally differ from the majority of data collected within mainstream psychology in several key respects – most notably in the diversity of forms of measurement and fewer number of subjects. We believe null hypothesis significance testing may not be the most appropriate method of analysis for comparative psychology for these reasons. Comparative psychology has a rich history of performing several analyses on a few subjects due to a philosophical interest in individual subject behavior, along with group assessments. Since first being published in 2011, Observation Oriented Modeling has successfully been used to analyze individual subjects’ responses from honey bees, horses, humans, and rattlesnakes. Observation Oriented Modeling is highly flexible and has allowed comparative researchers to perform a variety of assessments comparable to null hypothesis significance testing’s T-Tests, One-way ANOVA, and Repeated-Measures ANOVA while producing easily-interpretable and, most importantly, relevant results. This paper describes the diverse manners in which comparative psychologists can assess individual and group performances without concerns of statistical assumptions and limitations that complicate assessments when employing Null Hypothesis Significance Testing.


Replication and Pre-Registration in Comparative Psychology

There is growing interest and pressure in the social sciences to find ways to address the so-called “replication crisis” in psychology.  This includes increasing transparency and good practices in all areas of experimental research, and in particular to promote attempts at replication. Comparative psychology has a long history of efforts to replicate and extend previous research, but it is often difficult to do this when highly specialized methods or uncommon species are being studied.  I propose that comparative researchers make greater use of pre-registration as a way to ensure good practices, and I outline some of the ways in which this can be accomplished.

Automated Research in Comparative Psychology: Limitations and New Directions

Behavioral research is often enhanced by automated techniques, where experimental parameters and detection of behavior are controlled by electromechanical systems. Automated research promotes refinements in measurement, greater experimental control, longer durations of data collection, reduction of observer fatigue, and may permit new types of research to be conducted. In comparative psychology, use of automated techniques are often restricted to popular model organisms of fields such as behavior analysis and behavioral neuroscience. One factor contributing to this species-restriction may be the availability of automated research equipment, as most commercial research equipment is designed for rodents, and many researchers lack the skills required to create their own automated equipment. However, there are alternatives to commercial equipment, as some behavioral scientists have made available their own species-flexible, low-cost research equipment. In this paper, we provide three reviews. We first review recent trends in automated comparative psychology research, and then relate this to a second review on currently available automated research equipment. We also review affordable alternatives to commercial equipment that have been designed by behavioral scientists. Finally, we discuss useful technological skills that may allow comparative psychologists to take automation into their own hands and design equipment specific to their species and research topic.

The Importance of Comparative Psychology in Equine-Assisted Activities and Therapies

Practitioners of Equine Assisted Activities and Therapies (EAAT) use it to help individuals suffering from a wide range of physical and psychological disorders as an alternative practice in physical and psychotherapy.  Although there is plenty of research to support the benefits of these therapies, there is little research in equine behavior in this context, specifically how equine behaviors can best be utilized to improve the health of the human component.  Although much of EAAT uses horses in physical therapy, newer practices in EAAT focus on assisting individuals in building and improving interpersonal skills through practicing those skills with horses.  To fully understand and develop this area of EAAT, researchers need to look at the behavioral patterns of horses, how they learn and adapt to changes in human emotions and behaviors, and how these behaviors correspond to bonding with regards to friendships and relationships within the context of equine-human interactions.  To do this, scientists need to rely upon the principles of learning theory and behavioral sciences associated with comparative psychology.  The scientific methods used in comparative psychology are critical for researching these areas of EAAT.

Engaging Undergraduates in Comparative Psychology: A Case Study

With many comparative psychologists teaching at small colleges and universities where resources are limited, maintaining a traditional animal laboratory housing rats or pigeons is not realistic for many of these researchers. One way to overcome this lack of overhead costs and extensive lab space, is to forge collaborations with local zoos and aquariums. Zoo and aquarium research projects provide a way to examine a wide range of species, which is an important tenet within the field of comparative psychology. Furthermore, many undergraduates are innately attracted to the prospect of working with exotic animals. Here, we propose utilizing visitor behavior research as a means to provide undergraduates with research experience within the field comparative psychology, as well as expose the general public to animal behavior research.

The Value of Research in Comparative Cognition

Most research of comparative cognition has focused on the degree to which cognitive phenomena that have been reported in humans, especially children, can also be demonstrated in other animals. The value of such comparative research has not only been the finding that other animals show behavior that is qualitatively similar to that of humans but because the comparative approach calls for the careful control of variables often confounded with the mechanisms being tested, the comparative approach has identified procedures that could also improve the design of research with humans. The comparative approach has also been used to study the degree to which other animals demonstrate human biases and suboptimal behavior (e.g., commercial gambling). When applied to this field of research, the comparative approach has generally taken the position that human biases generally thought to be established by complex social and societal mechanisms (e.g., social reinforcement and entertainment) may be more parsimoniously accounted for by simpler mechanisms (i.e., conditioned reinforcement and positive contrast). When explained in terms of these mechanisms, the results have implications for explaining in simpler and more general terms the results of similar research with humans. Thus, comparative psychology tells us not only about the similarities and possible differences in behavior among species but it also may have implications for our understanding of similar behavior in humans.

Are there minding machines?

Are there minding machines? In this paper, I consult historical, philosophical, and empirical sources in trying to answer this intriguing question. My historical and philosophical discussions focus on five famous Frenchmen (Michele de Montaigne, René Descartes, Salomon de Caus, Julien Offray de La Mettrie, and Jacques Vaucanson) and one famous American (William James). My review of empirical research focuses on five topics in contemporary comparative cognition: associative/causal learning, short-term memory, number discrimination, relational cognition, and metacognition. I conclude that natural minding machines do exist; they are humans and animals. Minding may be said to mediate the complex changes in behavior that humans and animals overtly exhibit. In that same sense, computers and other mechanical devices are often considered to be artificial minding machines. Nevertheless, many thinkers deem such artificial minding machines to be pale replicas of natural minding machines that are built from the “wrong stuff.” No matter how much progress in artificial intelligence advances the computing power of these devices, they may never attain the intricacy and flexibility of nature’s minding machines.

A Place for Comparative Psychology in Undergraduate Curricula


Establishing a place for comparative psychology within the curricula of undergraduate psychology programs in the U.S. can be challenging. Psychology majors typically take a core set of required classes and select the remainder from a menu of options or from purely elective courses offered by faculty that are primarily focused on human behavior. It is within this context that many of us who teach comparative psychology find ourselves competing for space in our undergraduate programs. In this paper I describe a way to make comparative psychology more visible in undergraduate psychology programs. Specifically, I outline a strategy for mapping undergraduate courses in comparative psychology onto the American Psychological Association’s (2013) guidelines for the undergraduate major. The aim is to bring our unique  contributions into focus, offer clarity on common course objectives, and hopefully offer something useful for assessing undergraduate student learning.


Putting Comparative Psychology into a History and Systems of Psychology Course

For several reasons, a Comparative Psychology course has been absent from our curriculum since 2005, so students have had very little exposure to how and why psychologists study animals, and the place of animal research in the history of psychology. In the fall of 2015, out of necessity, five faculty in our department team-taught a History and Systems of Psychology course, which was our capstone at that time. My module focused the study of animals in psychology, including Comparative Psychology. One purpose was to highlight this side of Psychology, but also to show how the study of animals has led to current interest in Evolutionary Psychology. The content of this module is described here, as is a comparison of several journals, using number of pages published as a dependent variable, to show changes over time, as included in this module. It is intended that the information presented here might be of use to others seeking a way to incorporate more about animal research into their respective curricula in the absence of a course specifically about animal behavior research.

Appendix A and B

These appendixes summarize the graduate programs and points of contact for students interested in pursuing comparative psychology or a related fields in the field today. Both a google doc and a current list are provided. Individuals interested in having their programs or names included in the list, please contact Dr. Heather Hill at or

Brief Report

Performance on a means-end task by African elephants (Loxondonta africana): A replication study

The current study tested five female African elephants ( Loxondonta africana ) on a means-end behavioral task of pulling a support to retrieve a distant object; a replication of the Highfill, Spencer, Fad, and Arnold (2016) study. Each elephant was tested on three conditions of increasing difficulty. Specifically, subjects were asked to select from a choice of two trays where one tray was baited with a produce item and the other was A) empty; B) baited on the ground next to the tray; and C) baited on the far side of a break in the tray. Results indicated that all five elephants (3 adults, 2 calves) met the criteria established for conditions A and B, and the two calves met criteria for Condition C.  The performance by the adults was similar to the performance of the Asian elephants (all adults) in the previous study.

Effects of the type of reinforcer on renewal of operant responding

Some studies have identified that ABA renewal seems to depend on how response-reinforcer contingency is established. Using rats as subjects, the present study assessed ABA and ABB renewal using a two-component multiple schedule (VI30 s - VI30 s) each with a different reinforcer (pellets or sucrose). 16 subjects were trained to lever-press during 20 sessions in Context A; lever-pressing was extinguished during 10 sessions in Context B. And for the renewal test, 8 subjects were tested in Context A (Group ABA); whereas, the rest were tested in Context B (Group ABB). During acquisition, response rates were higher on the pellets component than the sucrose component; during extinction, response rates decreased to near-zero responses. A renewal effect was observed only for Group ABA during test, showing no differences between components. Our results suggest that different type of reinforcers do not seem to affect ABA renewal, using different contexts allows for renewal to be observed regardless of the differences in response rates during acquisition.



In Memoriam Jesse E. Purdy (1952-2018)

Jesse E. Purdy, a consummate comparative psychologist whose research started with laboratory rats but quickly expanded to include garter snakes, Weddell seals, cuttlefish, killer whales, coho salmon, and numerous more common species of fish, passed away on April 16, 2018, after a long and heroic battle with cancer. Purdy is survived by Karen, his wife of 45 years, and their two children, Kristopher and Matthew. He is also survived by his students and colleagues at Southwestern University who came to share his vision and enthusiasm for a life of inquiry and adventure and will continue to share that with their own students for decades to come.