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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 32, 2019

Issue cover

SI: ISCP bienniel meeting (2018)

The Role of Biological Significance in Human Learning and Memory

Deeply rooted within the history of experimental psychology is the search for general laws of learning that hold across tasks and species. Central to this enterprise has been the notion of equipotentiality; that any two events have the same likelihood of being associated with one another as any other pair of events. Much work, generally summarized as ‘biological constraints on learning,’ has challenged this view, and demonstrates pre-existing relations between cues and outcomes, based on genes and prior experience, that influence potential associability. Learning theorists and comparative psychologists have thus recognized the need to consider how the evolutionary history as well as prior experience of the organism being studied influences its ability to learn about and navigate its environment. We suggest that current models of human memory, and human memory research in general, lack sufficient consideration of how human evolution has shaped human memory systems. We review several findings that suggest the human memory system preferentially processes information relevant to biological fitness, and highlight potential theoretical and applied benefits afforded by adopting this functionalist perspective.

Adaptive Neural Networks Accounted for by Five Instances of “Respondent-Based” Conditioning

Neural Networks may be made much faster and more efficient by reducing the amount of memory and computation used. In this paper, a new type of neural network called an Adaptive Neural Network is introduced. The proposed neural network is comprised of five unique pairings of events. Each pairing is a module and the modules are connected within a single neural network. The pairings are a simulation of respondent conditioning. The simulations do not necessarily represent conditioning in actual organisms. In the theory presented here, the pairings in respondent conditioning become aggregated together to form a basis for operant conditioning. The specific pairings are as follows. The first pairing is between the reinforcer and the neural stimulus that elicits the behavior. This pairing strengthens and makes salient that eliciting neural stimulus. The second pairing is that of the now salient neural stimulus with the external environmental stimulus that precedes the operant behavior. The third is the pairing of the environmental stimulus event with the reinforcing stimulus. The fourth is the pairing of the stimulus elicited by the drive with the reinforcement event, changing the strength of the reinforcer. The fifth pairing is that after repeated exposure the external environmental stimulus is paired with the drive stimulus. This drive stimulus is generated by an intensifying drive.


Within each module, a “0” means no occurrence of a pairing  A of Stimuli A and a “1” means an occurrence of a pairing  A of Stimuli A. Similarly, a “0” means no occurrence of a pairing  B and a “1” means an occurrence of a pairing  B , and so on for all 5 pairings. To obtain an output one multiplies the values of pairings through E . In one trial or instance, all 5 pairings will occur. The results of the multiplications are then accumulated and divided by the number of instances. The use of these simple respondent pairings as a basis for neural networks reduces errors. Examples of problems that may be addressable by such networks are included.


Research Article

Domestication and the role of social play on the development of socio-cognitive skills in rats

Several studies on rats and hamsters, across multiple laboratories, have shown that limiting play in the juvenile period leads to adults that have physiological and anatomical changes in the medial prefrontal cortex (mPFC) and reduced socio-cognitive skills. Peers raised with playful peers have better socio-cognitive skills than animals raised with adult partners. Using Long Evans hooded rats - a commonly used domesticated strain - this relationship has been replicated multiple times. However, when the same paradigm was used with laboratory-reared wild rats, no differences were found between rats reared with peers and ones reared with adults. It has been shown that the key play-generated experiences involved are those related to actively wrestling with a partner and turn taking (as measured by role reversals), which give both partners opportunity to gain the advantage during play fighting. In the present study, we tested the hypothesis that wild rat adults provide juveniles more such experiences than do adult Long Evans rats. The asymmetry in the play interactions in adult-juveniles pairs was compared between the two strains. As predicted, wild rat adults initiated more play with the juveniles, wrestled more and provided more opportunities for role reversals. The findings thus support the hypotheses for the observed strain differences in the effects of rearing condition on the mPFC.

The role of outcome unit size in the collective foraging strategies of rats

The distribution of foraging strategies and associated activities of Wistar rats was examined, with food outcomes presented in small vs. large units. Groups of 4 rats foraged for food in a 4 x 3 array of covered holes, some containing 4 g of food. For some groups, food consisted of shelled sunflower seeds (small units); for other groups, food consisted of 3 pellets of chow (large units). Foraging strategies were classified as either production (seeking patches with food) or scrounging (tracking conspecifics). Production strategies were more common among groups that foraged for pellets instead of seeds. Producing food was highly correlated with contacting gates covering holes, whereas scrounging for food was highly correlated with following others in the group. The prevalence of activities associated with each foraging strategy was highly correlated with the proportion of time spent consuming food obtained from each activity (i.e., produced vs. scrounged food). Taken together, these findings suggest that, similar to other species, the finder’s advantage (low with small units, high with large units) modulates social foraging strategies in rats. A simple outcome-strategy feedback mechanism appears to mediate this modulation.

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Response-inhibition during problem solving in sheep

Response inhibition is a behavioural skill that is important for flexible behaviour and appropriate decision making. It requires the suppression of a prepotent, but inappropriate action, in order to achieve a more advantageous outcome. Response inhibition has been tested in many animal species using the cylinder task. This task requires the self-driven inhibition of an impulse to obtain a visible food reward via a detour, rather than a direct but blocked route. We have shown previously using the stop-signal task that sheep can successfully interrupt an already-started response, if a reward is going to be restricted. However, it is not known if sheep can show self-driven response inhibition in a task that provides a reward independent of performance. Here we tested two groups of sheep on the cylinder task (11 Lleyn sheep: aged 8 months; 8 Welsh mountain sheep aged ~8 years old). Sheep were trained using an opaque cylinder and all sheep successfully learned the task. When response inhibition was tested using the transparent cylinder, all sheep performed significantly better than chance, but the older sheep showed a reduced number of correct responses compared to the young sheep (72.5±5.0% and 86.4±4.3% respectively). The results show that sheep have a mechanism for self-regulating their actions in order to retrieve food faster.


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Three Levels of Consciousness: A Pattern in Phylogeny and Human Ontogeny

Investigations in the cognitive abilities of different animal species and children at different ages have revealed that consciousness comes in degrees. In this review, I will first address four cognitive abilities that are important to discriminate levels of consciousness: mirror self-recognition, theory of mind, mental time travel, and the capacity to entertain secondary representations. I will then examine putative relations between these abilities and assign them to three levels of consciousness (anoetic, noetic, autonoetic). Finally, I will discuss the implications of differences in consciousness for the understanding of behavioral organization in animals and humans and for animal welfare science. I will argue that, on one hand, implicit behavioral rules may account for results obtained in research on theory of mind and mental time travel abilities in animals and children. On the other hand, secondary representations may be the key to explain behaviors based on semantic memory as well as semantic future planning abilities observed in great apes and young children. These considerations are in accordance with the view that an explicit theory of mind and a continuous self through time are unique to humans.

Acoustic Localization Method Applied to the Analysis of Dolphin Calf Acoustical Exploratory Behavior Within its Social Group

Exploratory behavior includes all the actions that an animal performs to obtain information about a new object, environment, or individual through using its different senses of perception. Here, we studied the development of the exploratory behavior of a bottlenose dolphin (Tursiops truncatus) calf aged from 39 to 169 days by investigating its acoustic productions in relation to an immersed object handled by a familiar human without without the calf being isolated from the original social group. The study was conducted between July 2015 and January 2016 at Parc Asterix dolphinarium (Plailly, France). Simultaneous audio and video recordings were collected using a waterproof 360° audio-video system named BaBeL, which allows localization of the dolphin that is producing sounds. During 32 recording sessions, for a total duration of 6 hr 55 min of audio-video recordings, 46 click trains were attached to individual dolphins: 18 times to the calf, 11 times to its mother, and 17 times to another dolphin in the pool. When comparing the calf’s acoustical production to its mother’s, no significant differences were found in their click rate, mean click duration, or mean interclick interval (ICI). However, linear regression showed that calfs’ click rates increased with age and mean ICI decreased with age, probably due to an increase in its arousal. This nonintrusive methodology allows the description and analysis of acoustic signal parameters and acoustic exploratory behavior of a dolphin calf within its social group.

Aristotelean-Thomistic Approach of Comparative Psychology

The field of psychology has witnessed an increase in its reliance on empiricism to the point that many researchers operate with a complete disregard for the role of philosophy in their pursuit of knowledge. The resultant segmentation of the field and decline in such important areas as comparative psychology can be attributed to this trend, indicating the need for the role of both philosophical and scientific knowledge to be rightly applied and understood. A return to a proper utilization of philosophy in guiding empirical questions and interpreting results is offered as a means of revitalizing the field of comparative psychology. The philosophical approach of Aristotle and Thomas Aquinas is discussed as a means to do so, as it provides a valuable perspective in guiding research and enabling the scientist to interpret results in an integrated and informative manner, whereby the phenotypic comparisons of humans and non-humans can be understood coherently.


New Caledonian crows can interconnect behaviors learned in different contexts, with different consequences and after exposure to failure

Interconnection of behaviors is a process that describes how independently acquired behavioral repertoires can be combined together as a new sequence of behaviors. Manipulations of training, training context and experience of failure in the test situation can hinder this interconnection of previously acquired behaviors. We tested whether wild New Caledonian crows (Corvus moneduloides) could perform a sequence of six independently acquired behaviors in order to fetch a stone from inside a box in a nearby room and use it to gain food from a stone dropping apparatus. However, crows were only trained on three or four of the six behaviors required, and these prerequisites were trained in different contexts. One of the crows that learned four prerequisites solved the task. Neither of the crows that learned three prerequisites solved the task. The crows that learned four prerequisites, but did not solve the problem, were later trained in an additional behavior and then were able to solve the task. These results shows that New Caledonian crows are able to produce novel behavioral solutions to new problems by interconnecting behaviors learned in different contexts, with different consequences and despite experience of failure after the first exposure to the task.

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Targets, tactics, and cooperation in the play fighting of two genera of old world monkeys (Mandrillus and Papio): Accounting for similarities and differences

Play fighting in many species involves partners competing to bite one another while avoiding being bitten. Species can differ in the body targets that are bitten and the tactics used to attack and defend those targets. However, even closely related species that attack and defend the same body target using the same tactics can differ markedly in how much the competitiveness of such interactions is mitigated by cooperation. A degree of cooperation is necessary to ensure that some turn-taking between the roles of attacker and defender occurs, as this is critical in preventing play fighting from escalating into serious fighting. In the present study, the dyadic play fighting of captive troops of 4 closely related species of Old World monkeys, 2 each from 2 genera of Papio and Mandrillus, was analyzed. All 4 species have a comparable social organization, are large bodied with considerable sexual dimorphism, and are mostly terrestrial. In all species, the target of biting is the same – the area encompassing the upper arm, shoulder, and side of the neck – and they have the same tactics of attack and defense. However, the Papio species exhibit more cooperation in their play than do the Mandrillus species, with the former using tactics that make biting easier to attain and that facilitate close bodily contact. It is possible that species differences in how rigidly dominance relationships are maintained are expressed in the play of juveniles by altering the balance between competition and cooperation.

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Rats’ Choice in a Coordination Task

We designed a free-operant choice procedure that represents a technical improvement to assess the control of mutual reinforcement contingencies over the choice of coordinated behavior. We demonstrate the advantages of the new procedure with eight rats that were trained to continuously move a steel ball from end to end of a gutter. Subjects were assigned to pairs and had to choose between two response options: one in which reinforcement was contingent upon an individual response, and another in which reinforcement depended on the coordination of intra-pair behavior. We evaluated (a) the effect of reinforcement magnitude over the distribution of responses, and (b) the role of behavioral cues on the rats’ coordinated actions via dividing the experimental chamber in two compartments with a clear/opaque partition. The coordinated actions were more likely when the larger reinforcer was initially associated with the mutual reinforcement option. The visual interaction between subjects did not impact their coordinated actions. The possibility to control organisms’ preference for social or nonsocial alternatives opens potential lines of research. For instance, identifying how the coordination of activities combines with the future value of outcomes to produce stable cooperative equilibria.

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The frequency of solitary behaviours in captive odontocetes is modulated by environmental and social factors

The number of welfare-oriented studies is increasing in animals under human care, including odontocetes. However, validated welfare indicators are lacking for captive odontocetes. We studied the effect of several conditions (moment of the day, social grouping, public presence) and stimuli (enrichment, perturbations) on the solitary behaviour of Yangtze finless porpoises (Neophocaena asiaeorientalis asiaeorientalis), East-Asian finless porpoises (N. a. sunameri) and bottlenose dolphins (Tursiops truncatus). The frequency of solitary play increased in the three groups in positive conditions and decreased in negative contexts, which confirms that play is a useful indicator of welfare for captive odontocetes. Jumping seem to be indicative of stress for finless porpoises but could be ambiguous for bottlenose dolphins: indicating both positive and negative excitation. Stereotypical behaviours for Yangtze finless porpoises and environment hitting behaviours for bottlenose dolphins could indicate mild stress or frustration. Vigilant behaviours are not clear indicators since a high frequency could reflect boredom, but a low frequency was observed in poor social conditions. Finally, we suggest that environmental rubbing should be investigated further since our results for this behaviour were not clear.

Capuchin (Sapajus [Cebus] apella) Change Detection

Change blindness is a phenomenon in which individuals fail to detect seemingly obvious changes in their visual fields.  Like humans, several animal species have also been shown to exhibit change blindness; however, no species of New World monkey has been tested to date.  Nine capuchins (Sapajus [Cebus] apella) were trained to select whether or not a stimulus changed on a computerized task.  In four phases of testing, consisting of full image changes, subtle occlusion changes, and two levels of feature location changes, the search display and mask durations were systematically varied to determine whether capuchins experienced change blindness and in what contexts.  Only the full image change test yielded significant results, with subjects detecting changes most accurately with longer search displays and, perplexingly, least accurately when there was no mask.  No interactions between search display and mask durations were found in any test phase, suggesting that the relationship between the two parameters may not be important to how capuchins perceive changes.  While it is possible that capuchins do not experience change blindness, we suspect that a mix of experimental design, the difficulty of the task, and the inability to verify how closely the subjects attended to each trial contributed to the lack of significant results.

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Very superstitious? A preliminary investigation of pigeons’ body position during a matching-to-sample task under differential and common outcome conditions.

The delayed matching-to-sample (DMS) task is widely employed to assess memory in a range of non-human animals. On the standard “common outcomes” (CO) DMS task, correct performance following either sample stimulus results in reinforcement. In contrast, on a “differential outcomes” (DO) DMS task, the outcome following either sample stimulus is different. One of the most consistent findings in the comparative literature is that performance under a DO condition is superior to that under a CO condition. The superior performance is attributed to the fact the DO condition enhances memory for the sample stimulus by tagging each sample with a discrete reward. Here, we investigate an alternative possibility, that pigeons use positional mediation during the delay under DO, but not CO, conditions. To test this, we tracked the head position of pigeons performing a DO (n = 4) or CO (n = 4) task. Consistent with the positional mediation account, all subjects in the DO condition displayed evidence of positional mediation. Surprisingly, positional mediation was not unique to subjects in the DO condition, with subjects in the CO condition also displaying evidence of mediation.


Brief Report

A Facet Theory Analysis of the Structure of Cognitive Performance in New Zealand Robins (Petroica longipes)

In this report we analyse the cognitive performance of New Zealand Robins (Petroica longipes) using facet theory, smallest space analysis (SSA) and partial order scalogram analysis (POSA). The data set we analyse was originally subjected to principle component analysis in order to develop a test-battery for avian cognitive performance. We extend these analyses by proposing a two facet rather than a single component solution using SSA and we characterize individual birds by their scores on all tasks using POSA. We note problems with the small sample size and call for our exploratory analyses to be replicated using a larger sample of birds and for the development of further test items using the facet theory’s tool the mapping sentence. We suggest that facet theory and the mapping sentences are research approaches suitable for conceiving, designing, analysing and developing theory that may be used within avian cognitive research. We conclude by proposing a mapping sentence for avian cognition, which forms an adaptable template for future avian cognition research.

Drinks Like a Fish: Neural Maturation Mitigates the Effects of Ethanol on Associative Learning in Zebrafish (Danio rerio)

The present study sought to elucidate whether neural maturation has a mitigating effect on ethanol and its concomitant effects on memory. Three-month old zebrafish were acclimated to a plus maze using a habituation procedure. After acclimatization to the maze, associations between the red cue cards and reward were formed via a shaping procedure. Following the final shaping day, food was removed from the maze and red cues were only present in one arm. The time it took for the fish to go from the start box to the cued arm was then measured. Afterwards, fish were exposed to 0.00, 0.25, or 0.75% ethanol (v/v) for 72 hours. Post-exposure memory performance was tested at 0.5-day, 5-day, and 14-day endpoints. Three primary findings were noted. First, no significant difference in run time was found within the control group at any time point, suggesting an adept associative memory system in zebrafish. Second, no significant difference in run time was found when comparing 0.25 and 0.75% (v/v) ethanol groups. Therefore, these treatments were pooled for further analyses. Third, the most significant impairment was observed at the 0.5-day post exposure time point indicating that ethanol has a significant impact on recently learned associations. Finally, no significant difference in run time was observed within the pooled treatment group on subsequent time points. This capacity for recovery was a key difference from what was observed in previous studies.

Spatial memory in hamsters (Mesocricetus auratus): Depleting/Replenishing environments and pre-choice behaviors in the Radial Arm Maze

Rodents’ spatial memory is traditionally assessed in the radial arm-maze (RAM). An accurate response pattern in the RAM is described as the tendency to visit a new arm after each choice (i.e. win-shift strategy). When this response pattern is found, it is said that the animal remembers the places visited. In the present experiment, 12 hamsters were assessed in the RAM under two conditions: the depleting condition, in which feeders were not rebaited after each visit; and the replenishing condition, in which, feeders were rebaited. We registered the number of new arms visited (hits), the time spent in the central area of the maze, and the behaviors emitted in the central area before each arm choice. Results showed that, regardless of condition, animals were significantly more likely to visit new arms. However, more pre-choice behaviors and a longer center time were observed in the depleting condition than in the replenishing one. It is discussed that hamsters have a win-shift strategy for hoarding behavior even when they do not need to remember the places visited, though they exhibited more pre-choice behaviors when searching for food in the depleting condition.

A Comparison of Sequential Learning Errors Made by Apes and Monkeys Reveals Individual but not Species Differences in Learning

Using methods comparable to those used previously to test closely-related taxa (Pan troglodytes and Macaca mulatta), our aim was to better understand how gorillas (Gorilla gorilla gorilla) and Japanese macaques (M. fuscata) learn sequences. Using a disappearing-type simultaneous chain, we trained five gorillas and eight macaques on a two-item list of colored stimuli presented via touchscreens. There was no difference across species in the number of trials required to learn the two-item list. We added a third item to the list as each subject reached criterion. We then analyzed the subjects’ first 30 trials with the three-item list and found that the rate of successfully sequencing the list varied by subject but not by species. In their first 30 trials of the three-item list, subjects selected the second item correctly only at chance, suggesting they had only encoded the first symbol when learning the two-item list. One gorilla, tested on longer sequences, showed similar responses: when first presented with a newly-lengthened list, he only selected the penultimate item at chance levels. Thus, the primates’ errors with newly-lengthened lists is suggestive of the chaining theory of learning. These results highlight similarities in list learning of these two distantly-related primate species as well as the clear intra-species variation in learning.

A Portable System for Detecting Infrasound Using a Microcontroller

The purpose of this project was to create a device to detect infrasound communication from elephants. The device was designed and prototyped to be capable of monitoring an input signal for infrasound. If infrasound is detected, an audible alarm is sounded. This device can record audio signals for long periods of time to a digital storage device. It can be utilized for other areas of study with some modification. For example, by selecting appropriate sensors the device can be used for studying vibrations in structures. The device is low-cost so it would be able to be procured more easily and in higher quantities than more expensive and cumbersome laboratory monitoring equipment. This device could also be used as an educational and research device for students studying animal behavior in the field and laboratory. Infrasound is not limited to only elephants, but hippopotamuses, rhinoceroses and giraffes also communicate with infrasound. Environmental infrasound from sources such as wind turbines, sonic booms, explosions, tornadoes, and earthquakes can also be monitored.

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Special Issue: Revisiting The Legacy of Stan Kuczaj

Pre-and Post-Partum Whistle Production of a Bottlenose Dolphin (Tursiops truncatus) Social Group

The signature whistle of the Atlantic bottlenose dolphin ( Tursiops truncatus ) is a well-studied acoustic signal know for broadcasting identity and maintaining contact with conspecifics. Several studies have investigated the use of this signal surrounding the birth of calves to dolphin social groups, although there appears to be discrepancies between the findings of these studies. We aimed to add to the current literature in an attempt to reconcile some of these inconsistencies through investigation of signature whistle production by a bottlenose dolphin group two months prior to and two months following the birth of a calf to one of the social group members. We found that the production of signature whistles matching the contour belonging to our dolphin mother increased significantly in both the pre- and post-partum period. Heightened production of the mother’s signature whistle type in the first week of our focal calf’s life supports the establishment of a recognition system within this time period. Given that learning processes associated with the sound environment appear to begin shortly after calf birth, we also explored the signature whistle rates of the other social group members in an effort to determine whether any signature whistle production influenced the development of the dolphin calf’s own signature whistle type. We found that the signature whistles of the other social group members were significantly lower than production of the mother’s signature whistle until after the first week post-partum. None of the signature whistle types appeared to influence the signature whistle development of our focal calf within the scope of this study, however, as the calf did not develop a signature whistle in her first two months of life.

Common bottlenose dolphin, Tursiops truncatus, seasonal habitat use and associations with habitat characteristics in Roanoke Sound, North Carolina

Understanding how habitat characteristics influence common bottlenose dolphin, Tursiops truncatus, distribution and behavior can be useful for conservation. The dolphin community in Roanoke Sound, North Carolina primarily exhibits seasonal residency and there is limited information on their habitat use. The objectives of this study were to increase habitat use knowledge and determine the relationship between habitat characteristics and dolphin distribution using standardized photographic-identification data (2009 – 2017). A hot spot (Getis-Ord Gi*) analysis showed dolphins frequently use the southern region containing the mouth of the estuary for feeding and traveling. Habitat characteristics were modeled with zero-altered gamma (ZAG), generalized linear (GLM), and generalized additive (GAM) models to predict dolphin group density. Models showed that groups were more likely to be present in areas with greater benthic slope variation and shallow areas closer to land, and that different habitat characteristics were associated with feed, social, and travel activities. This study suggests that Roanoke Sound provides a seasonal foraging area and travel corridor between the estuaries and coastal waters. This information contributes baseline knowledge of how habitat potentially influences dolphin distribution and behavior which can be useful for management and conservation, especially in areas where habitat changes and impacts need to be assessed.

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Special Issue on Contact

Methodological Considerations for Comparison of Cross-species Use of Tactile Contact

Cross-species comparisons are benefited by compatible datasets; conclusions related to phylogenetic comparisons, questions on convergent and divergent evolution, or homologs versus analogs can only be made when the behaviors being measured are comparable. A direct comparison of the social function of physical contact across two disparate taxa is possible only if data collection and analyses methodologies are analogous. We identify and discuss the parameters, assumptions and measurement schemes applicable to multiple taxa and species that facilitate cross-species comparisons. To illustrate our proposed guidelines for evaluating the role played by tactile contact in social behavior across disparate taxa, this paper presents data on mother-offspring relationships in the two species studied by the authors: chimpanzees (Pan troglodytes schweinfurthii) and dolphins (bottlenose and spotted, Tursiops truncatus and Stenella frontalis, respectively). Cross-species comparative studies allow for a more comprehensive assessment of the similarities and differences with respect to how animals traverse the relationships that form their social groups and societies.