Crows and common ravens do not reciprocally exchange tokens with a conspecific to gain food rewards

Human economic transactions are based on complex forms of reciprocity, which involve the capacities to share and to keep track of what was given and received over time. Animals too engage in reciprocal interactions, but mechanisms such as calculated reciprocity have only been shown experimentally in few species. Various forms of cooperation, for example food and information sharing, are frequently observed in corvids, and they can engage in exchange interactions with human experimenters and accept delayed rewards. Here, we tested whether crows and common ravens would reciprocally exchange tokens with a conspecific in an exchange task. Birds received a set of three different types of tokens, some valuable for themselves, that is, they could exchange them for a food reward with a human experimenter, some valuable for their partner and some without value. The valuable tokens differed between the birds, which means that each bird could obtain more self-value tokens from their partner's compartment. We did not observe any active transfers, that is one individual giving a token to the experimental partner by placing it in its beak. We only observed 6 indirect transfers, that is one individual transferring a token into the compartment of the partner (3 no-value, 1 partner-value and 2 self-value tokens) and 67 “passive” transfers, that is one subject taking the token lying in reach in the compartment of the partner. Individuals took significantly more self-value tokens compared with no-value and partner-value tokens. This indicates a preference for tokens valuable to focal individuals. Significantly more no-value tokens compared with partner-value tokens were taken, likely to be caused by experimental partners exchanging self-value tokens with the human experimenter, and therefore, more no-value tokens being available in the compartment. Our results presently do not provide empirical support for reciprocity in crows and ravens, most likely caused by them not understanding the potential roles of receiver and donor. We therefore suggest further empirical tests of calculated reciprocity to be necessary in corvids.     

Language-trained chimpanzees (Pan troglodytes) delay gratification by choosing token exchange over immediate reward consumption

Token exchange inherently introduces an element of delay between behavior and reward and so token studies may help us better understand delay of gratification and self-control. To examine this possibility, we presented three language-trained chimpanzees with repeated choices involving different foods that could be eaten immediately or lexigram (graphic symbol) tokens that represented (and could be traded for) foods later. When both options were foods, chimpanzees always chose more preferred foods over less preferred foods. When both options were lexigram tokens representing those same foods, performance remained the same as chimpanzees selected the higher value token and then traded it for food. Then, when faced with choosing a token that could be traded later or choosing a food item that could be eaten immediately, most chimpanzees learned to make whatever response led to the more preferred food. They did this even when that meant selecting a high value lexigram token that could be traded only 2 to 3 min later instead of a medium value, but immediately available, food item. Thus, chimpanzees flexibly selected tokens even though such selections necessarily delayed gratification and required forgoing immediately available food. This finding illustrates the utility of symbolic token exchange for assessing self-control in nonhuman animals.     

How Social Context,Token Value,and Time Course Affect Token Exchange in Capuchin Monkeys (<Emphasis Type="Italic">Cebus apella</Emphasis>)

Although numerous studies have examined token-directed behaviors in primates, few have done so in a social context despite the fact that most primate species live in complex groups. Here, we provided capuchin monkeys with a relatively limited budget of tokens, likely to elicit intragroup competition, and, after an overnight delay, we allowed them to exchange tokens while in a group setting. We aimed to 1) evaluate whether social context affects token-directed behaviors of knowledgeable subjects, i.e., subjects already proficient in token exchange before the present study, as well as of naïve subjects, i.e., subjects that never showed exchange behavior before this study; 2) appraise whether capuchins indeed value tokens; and 3) assess whether capuchins can refrain from throwing tokens outside their enclosure when the experimenter is not present. Overall, the social context positively affected high-ranking individuals and negatively affected low-ranking ones. All 6 high-ranking naïve subjects, but none of the 4 low-ranking ones, quickly acquired token exchange behavior, whereas 9 of 12 low-ranking knowledgeable subjects, but only 1 high-ranking knowledgeable subject, never displayed token exchange in social contexts. Thus, competition constrained token exchange in low-ranking subjects and prompted exchange behavior in high-ranking naïve subjects. Capuchins were unable to inhibit the exchange of valueless items when the experimenter was soliciting them and, at the group level, knowledgeable subjects did not exchange more valuable tokens than less valuable (or valueless) ones. However, the 3 high-ranking knowledgeable subjects that exchanged most of the tokens first preferentially exchanged more valuable tokens over less valuable or valueless ones. Finally, capuchins inhibited exchange behavior in the absence of the experimenter, thus recognizing the appropriate conditions in which a successful exchange could occur.     

Macaque Monkeys Can Learn Token Values from Human Models through Vicarious Reward

Monkeys can learn the symbolic meaning of tokens, and exchange them to get a reward. Monkeys can also learn the symbolic value of a token by observing conspecifics but it is not clear if they can learn passively by observing other actors, e.g., humans. To answer this question, we tested two monkeys in a token exchange paradigm in three experiments. Monkeys learned token values through observation of human models exchanging them. We used, after a phase of object familiarization, different sets of tokens. One token of each set was rewarded with a bit of apple. Other tokens had zero value (neutral tokens). Each token was presented only in one set. During the observation phase, monkeys watched the human model exchange tokens and watched them consume rewards (vicarious rewards). In the test phase, the monkeys were asked to exchange one of the tokens for food reward. Sets of three tokens were used in the first experiment and sets of two tokens were used in the second and third experiments. The valuable token was presented with different probabilities in the observation phase during the first and second experiments in which the monkeys exchanged the valuable token more frequently than any of the neutral tokens. The third experiments examined the effect of unequal probabilities. Our results support the view that monkeys can learn from non-conspecific actors through vicarious reward, even a symbolic task like the token-exchange task.     

Do capuchin monkeys (Cebus apella) use tokens as symbols?

In the absence of language, the comprehension of symbols is difficult to demonstrate. Tokens can be considered symbols since they arbitrarily stand for something else without having any iconic relation to their referent. We assessed whether capuchin monkeys (Cebus apella) can use tokens as symbols to represent and combine quantities. Our paradigm involved choices between various combinations of tokens A and B, worth one and three rewards, respectively. Pay-off maximization required the assessment of the value of each offer by (i) estimating token numerousness, (ii) representing what each token stands for and (iii) making simple computations. When one token B was presented against one to five tokens A (experiment 1), four out of ten capuchins relied on a flexible strategy that allowed to maximize their pay-off, i.e. they preferred one token B against one and two tokens A, and they preferred four or five tokens A against one token B. Moreover, when two tokens B were presented against three to six tokens A (experiment 2), two out of six capuchins performed summation over representation of quantities. These findings suggest that capuchins can use tokens as symbols to flexibly combine quantities.     

Non-human primate token use shows possibilities but also limitations for establishing a form of currency

Non-human primates evaluate choices based on quantitative information and subjective valuation of options. Non-human primates can learn to value tokens as placeholders for primary rewards (such as food). With those tokens established as a potential form of ‘currency’, it is then possible to examine how they respond to opportunities to earn and use tokens in ways such as accumulating tokens or exchanging tokens with each other or with human experimenters to gain primary rewards. Sometimes, individuals make efficient and beneficial choices to obtain tokens and then exchange them at the right moments to gain optimal reward. Sometimes, they even accumulate such rewards through extended delay of gratification, or through other exchange-based interactions. Thus, non-human primates are capable of associating value to arbitrary tokens that may function as currency-like stimuli, but there also are strong limitations on how non-human primates can integrate such tokens into choice situations or use such tokens to fully ‘symbolize’ economic decision-making. These limitations are important to acknowledge when considering the evolutionary emergence of currency use in our species.This article is part of the theme issue ‘Existence and prevalence of economic behaviours among non-human primates’.     

Response-cost punishment via token loss with pigeons

Two experiments were conducted to investigate punishment via response-contingent removal of conditioned token reinforcers (response cost) with pigeons. In Experiment 1, key pecking was maintained on a two-component multiple second-order schedule of token delivery, with light emitting diodes (LEDs) serving as token reinforcers. In both components, responding produced tokens according to a random-interval 20-s schedule and exchange periods according to a variable-ratio schedule. During exchange periods, each token was exchangeable for 2.5-s access to grain. In one component, responses were conjointly punished according to fixed-ratio schedules of token removal. Response rates in this punishment component decreased to low levels while response rates in the alternate (no-punishment) component were unaffected. Responding was eliminated when it produced neither tokens nor exchange periods (Extinction), but was maintained at moderate levels when it produced tokens in the signaled absence of food reinforcement, suggesting that tokens served as effective conditioned reinforcers. In Experiment 2, the effect of the response-cost punishment contingency was separated from changes in the density of food reinforcement. This was accomplished by yoking either the number of food deliveries per component (Yoked Food) or the temporal placement of all stimulus events (tokens, exchanges, food deliveries) (Yoked Complete), from the punishment to the no-punishment component. Response rates decreased in both components, but decreased more rapidly and were generally maintained at lower levels in the punishment component than in the yoked component. In showing that the response-cost contingency had a suppressive effect on responding in addition to that produced by reductions in reinforcement density, the present results suggest that response-cost punishment shares important features with other forms of punishment.     

Cooperation Improves Success during Intergroup Competition: An Analysis Using Data from Professional Soccer Tournaments

The benefit mutually gained by cooperators is considered the ultimate explanation for why cooperation evolved among non-relatives. During intergroup competition, cooperative behaviours within groups that provide a competitive edge over their opposition should be favoured by selection, particularly in lethal human warfare. Aside from forming larger groups, three other ways that individuals within a group can cooperate to improve their chances of gaining a mutual benefit are: (i) greater networking, (ii) contributing more effort, and (iii) dividing labour. Greater cooperation is expected to increase the chances of gaining a group benefit by improving proficiency in the tasks critical to success—yet empirical tests of this prediction using real-world cases are absent. In this study, we used data derived from 12 international and professional soccer competitions to test the predictions that: 1) greater levels of cooperative behaviour are associated with winning group contests, 2) the three forms of cooperation differ in relative importance for winning matches, 3) competition and tournament-type affect the levels of cooperation and shooting proficiency in matches, and 4) greater levels of networking behaviour are associated with increased proficiency in the most critical task linked with winning success in soccer—shooting at goal. Winners were best predicted by higher shooting proficiency, followed by greater frequencies of networking interactions within a team but unexpectedly, fewer networking partners and less division of labour. Although significant variation was detected across competitions and tournament-types, greater levels of networking behaviour were consistently associated with increased proficiency in shooting at goal, which in turn was linked with winning success. This study empirically supports the idea that intergroup competition can favour cooperation among non-relatives.     

Learning a functional grammar of protein domains using natural language word embedding techniques

In this paper, using Word2vec, a widely-used natural language processing method, we demonstrate that protein domains may have a learnable implicit semantic “meaning” in the context of their functional contributions to the multi-domain proteins in which they are found. Word2vec is a group of models which can be used to produce semantically meaningful embeddings of words or tokens in a fixed-dimension vector space. In this work, we treat multi-domain proteins as “sentences” where domain identifiers are tokens which may be considered as “words.” Using all InterPro (Finn et al. 2017) pfam domain assignments we observe that the embedding could be used to suggest putative GO assignments for Pfam (Finn et al. 2016) domains of unknown function.     

Responses to a simple barter task in chimpanzees, Pan troglodytes

Chimpanzees (Pan troglodytes) frequently participate in social exchange involving multiple goods and services of variable value, yet they have not been tested in a formalized situation to see whether they can barter using multiple tokens and rewards. We set up a simple barter economy with two tokens and two associated rewards and tested chimpanzees on their ability to obtain rewards by returning the matching token in situations in which their access to tokens was unlimited or limited. Chimpanzees easily learned to associate value with the tokens, as expected, and did barter, but followed a simple strategy of favoring the higher-value token, regardless of the reward proffered, instead of a more complex but more effective strategy of returning the token that matched the reward. This response is similar to that shown by capuchin monkeys in our previous study. We speculate that this response, while not ideal, may be sufficient to allow for stability of the social exchange system in these primates, and that the importance of social barter to both species may have led to this convergence of strategies.     

An effect of inter-trial duration on the gambler's fallacy choice bias

The gambler's fallacy is defined as the avoidance of a winning outcome in a stochastic environment with a constant probability. We tested the possibility that the gambler's fallacy in humans is responsive to the amount of time between choice allocations. Two groups of subjects were placed in a six-choice betting game in which the choices were clustered into two “patches.” Groups were defined by the length of time - 2 s or 6 s - between trials. On any given trial subjects allocated six points among the alternatives, and retained any points that were bet on the winning alternative. Both groups showed evidence of the gambler's fallacy bias. However, the bias was stronger in the 6-s ITI group than in the 2-s ITI group. This difference was found primarily to be due to differences in the number of subjects showing an opposing bias to the gambler's fallacy, namely a preference for the most recent winning alternative. This choice bias is termed the hot hand fallacy. Our findings contradict predictions derived from a foraging heuristic and from traditional accounts of the gambler's fallacy.     

Persistence of Winner and Loser Effects Depends on the Behaviour Measured

Recent contest experience can influence an individual’s behaviour in subsequent contests. When the probability of winning a subsequent contest is used to quantify experience effects, a loser effect usually lasts longer than a winner effect. This conclusion, however, may be caused by this probability understating the persistence of the influence of a winning experience on contest decisions. Using Kryptolebias marmoratus, a mangrove killifish, as the study organism, we investigated whether different conclusions about the relative persistence of winning and losing experiences would be reached when different aspects of contest behaviour (probability of initiating attacks, probability of winning non‐escalated and escalated contests, escalation rate and contest duration) were measured. The results indicated that the apparent persistence of the effect of winning or losing experiences varied with the behaviour studied. When the likelihood to initiate attacks was used, no winner effect was detected while the loser effect lasted for <1 d. When escalation rate was used, the winner effect lasted for 2–4 d, while the loser effect lasted for 1–2 d. When the probability of winning non‐escalated contests was used, the winner effect was detectable for <1 d, while the loser effect lasted for 2–4 d. And, when contest duration was used, the winner effect was detectable for 2–4 d, but no loser effect was detectable. These results show that (1) the probability of winning a subsequent contest understated the persistence of the influence of a winning experience on the fish’s contest decisions, (2) the measures most effective at detecting winner effects are different from those most effective at detecting loser effects and (3) in K. marmoratus, both effects can be detected 2 d after the completion of experience training but both dissipate in 4 d.     

Psychological complications after stillbirth--influence of memories and immediate management: population based study.

OBJECTIVE--To identify factors that may predict long term psychological complications among women who have had a stillborn child. DESIGN--Nationwide population based study using epidemiological methods. SUBJECTS--380 subjects and 379 controls who had had a stillborn or non-deformed live child in Sweden in 1991. RESULTS--Information was provided by 636 (84%) women. The ratio (95% confidence interval) of proportions of women with symptoms related to anxiety above the 90th centile for women who had had a stillborn child compared with those who had not was 2.1 (1.2 to 3.9). An interval of 25 hours or more from the diagnosis of death in utero to the start of delivery gave a ratio of 4.8 (1.5 to 15.9). The ratio was 2.3 (1.1 to 5.3) for not seeing the child as long as the mother had wished and 3.1 (1.6 to 6.0) for no possession of a token of remembrance. CONCLUSION--It is advisable to induce the delivery as soon as feasible after the diagnosis of death in utero. A calm environment for the woman to spend as much time as she wants with her stillborn child is beneficial, and tokens of remembrance should be collected.     

A concept of value during experimental exchange in brown capuchin monkeys, Cebus apella

We evaluated the response of brown capuchin monkeys to two differentially valued tokens in an experimental exchange situation akin to a simple barter. Monkeys were given a series of three tests to evaluate their ability to associate tokens with food, then their responses were examined in a barter situation in which tokens were either limited or unlimited. Capuchins did not perform barter in the typical sense, returning the tokens which were associated with the reward. However, females, but not males, showed a different response, preferring the higher-value token. This may indicate that they learned to prefer one token over the other rather than to associate the tokens with their specific rewards. This sex difference parallels previous findings of greater reciprocity in female brown capuchins than in males.     

Tokens improve capuchin performance in the reverse–reward contingency task

In humans and apes, one of the most adaptive functions of symbols is to inhibit strong behavioural predispositions. However, to our knowledge, no study has yet investigated whether using symbols provides some advantage to non-ape primates. We aimed to trace the evolutionary roots of symbolic competence by examining whether tokens improve performance in the reverse–reward contingency task in capuchin monkeys, which diverged from the human lineage approximately 35 Ma. Eight capuchins chose between: (i) two food quantities, (ii) two quantities of ‘low-symbolic distance tokens’ (each corresponding to one unit of food), and (iii) two ‘high-symbolic distance tokens’ (each corresponding to a different amount of food). In all conditions, subjects had to select the smaller quantity to obtain the larger reward. No procedural modifications were employed. Tokens did improve performance: five subjects succeeded with high-symbolic distance tokens, though only one succeeded with food, and none succeeded with low-symbolic distance tokens. Moreover, two of the five subjects transferred the rule to novel token combinations. Learning effects or preference reversals could not account for the successful performance with high-symbolic distance tokens. This is, to our knowledge, the first demonstration that tokens do allow monkeys to inhibit strong behavioural predispositions, as occurs in chimpanzees and children.     

Body condition,live weight and success in agonistic encounters in mixed parity groups of sows during gestation

Group housing of gestating sows benefits their welfare by allowing them freedom of movement and the opportunity for social interaction. However, social life could also bring disadvantages for individuals who receive direct aggression or are displaced from the feeder. The aim of this study was to investigate associations between social behaviour, body condition and live weight. Gestating sows (n=298) were investigated on a commercial farm. Sows were housed in mixed parity groups where two single space, ad libitum trough feeders served 12 animals. Sows were weighed, body condition scored and had their back fat layer measured at mixing, 4 weeks after insemination and again before farrowing. Social status was estimated based on the numbers of won and lost agonistic interactions at mixing and at the end of gestation. In addition, tear staining was scored before the farrowing and reproductive performance data were collected. With the aid of video recordings, 100 to 150 interactions per group were observed. Winning percentage at mixing and at the end of gestation were associated (P<0.05) and appeared relatively stable within individuals. Tear staining scores and litter sizes were not associated with winning percentage at the end of gestation. However, live weight, relative weight, body condition and back fat thickness were associated with winning percentage (P<0.05), giving heavier animals an advantage. Low winning percentage related to lower live weight gain, probably due to poorer success in competition for feed. Live weight within a mixed parity group could be used as a proxy measure for social status. Sows with low body condition score and submissive sows might need special attention with regard to group dynamics and housing to alleviate the effects of competition in group housing.     

Biomedical research funding: when the game gets tough, winners start to play

Extramural funding provides major support for biomedical research in academia, and National Institutes of Health (NIH) grants often constitute direct evaluation criteria for promotions and tenure. Therefore, NIH budget trends influence long-term scientific strategies and career decisions, as well as the progress of science itself. Our analysis of the last 37 years of NIH awards, however, reveals that the success rate of grant applications submitted for funding is negatively related to the total yearly amount of (inflation-adjusted) NIH extramural expenditure. Instead, as might be expected, the ratio between available funding and the number of submission directly predicts the probability of winning support in any given year. We purport that the considerable success rate variability can be parsimoniously explained by a proportional but delayed reaction of the number of applications to budget fluctuations. As a counterintuitive consequence, grant proposals conceived during lean periods might stand the best chance of success.     

Intergroup variation in robbing and bartering by long-tailed macaques at Uluwatu Temple (Bali,Indonesia)

Robbing and bartering (RB) is a behavioral practice anecdotally reported in free-ranging commensal macaques. It usually occurs in two steps: after taking inedible objects (e.g., glasses) from humans, the macaques appear to use them as tokens, returning them to humans in exchange for food. While extensively studied in captivity, our research is the first to investigate the object/food exchange between humans and primates in a natural setting. During a 4-month study in 2010, we used both focal and event sampling to record 201 RB events in a population of long-tailed macaques (Macaca fascicularis), including four neighboring groups ranging freely around Uluwatu Temple, Bali (Indonesia). In each group, we documented the RB frequency, prevalence and outcome, and tested the underpinning anthropogenic and demographic determinants. In line with the environmental opportunity hypothesis, we found a positive qualitative relation at the group level between time spent in tourist zones and RB frequency or prevalence. For two of the four groups, RB events were significantly more frequent when humans were more present in the environment. We also found qualitative partial support for the male-biased sex ratio hypothesis [i.e., RB was more frequent and prevalent in groups with higher ratios of (sub)adult males], whereas the group density hypothesis was not supported. This preliminary study showed that RB is a spontaneous, customary (in some groups), and enduring population-specific practice characterized by intergroup variation in Balinese macaques. As such, RB is a candidate for a new behavioral tradition in this species.     

Human visual search does not maximize the post-saccadic probability of identifying targets

Researchers have conjectured that eye movements during visual search are selected to minimize the number of saccades. The optimal Bayesian eye movement strategy minimizing saccades does not simply direct the eye to whichever location is judged most likely to contain the target but makes use of the entire retina as an information gathering device during each fixation. Here we show that human observers do not minimize the expected number of saccades in planning saccades in a simple visual search task composed of three tokens. In this task, the optimal eye movement strategy varied, depending on the spacing between tokens (in the first experiment) or the size of tokens (in the second experiment), and changed abruptly once the separation or size surpassed a critical value. None of our observers changed strategy as a function of separation or size. Human performance fell far short of ideal, both qualitatively and quantitatively.     

Winning fights elevates testosterone levels in California mice and enhances future ability to win fights

The 'winner effect' has been studied in a variety of species, but only rarely in mammals. We compared effects of winning three, two, one, or zero resident-intruder encounters on the likelihood of winning a subsequent aggressive encounter in the California mouse (Peromyscus californicus). During the training phase, we ensured that resident males won all encounters by staging contests with mildly sedated, smaller intruders. During the test phase, the resident male encountered an unfamiliar, more evenly matched intruder that had experience winning an encounter and was larger than the resident. Testosterone (T) plasma levels significantly increased after the final test when they had experienced two prior winning encounters, and the probability of winning a future encounter increased significantly after three prior wins independent of intrinsic fighting ability. We hypothesize a 'winner-challenge' effect in which increased T levels serve to reinforce the winner effect in male California mice.