Do monkeys compare themselves to others?

Social comparisons are a fundamental characteristic of human behaviour, yet relatively little is known about their evolutionary foundations. Adapting the co-acting paradigm from human research (Seta in J Pers Soc Psychol 42:281–291, 1982. doi: 10.1037//0022-3514.42.2.281), we examined how the performance of a partner influenced subjects’ performance in long-tailed macaques (Macaca fascicularis). Using parallel testing in touch screen setups in which subjects had to discriminate familiar and novel photographs of men and women, we investigated whether accuracy and reaction time were influenced by partner performance and relationship quality (affiliate vs. non-affiliate). Auditory feedback about the alleged performance of the co-actor was provided via playback; partner performance was either moderately or extremely better or worse than subject performance. We predicted that subjects would assimilate to moderately different comparison standards as well as to affiliates and contrast away from extreme standards and non-affiliates. Subjects instantly generalized to novel pictures. While accuracy was not affected by any of the factors, long reaction times occurred more frequently when subjects were tested with a non-affiliate who was performing worse, compared to one who was doing better than them (80 % quantile worse: 5.1, better: 4.3 s). For affiliate co-actors, there was no marked effect (worse: 4.4, better: 4.6 s). In a control condition with no auditory feedback, subjects performed somewhat better in the presence of affiliates (M = 77.8 % correct) compared to non-affiliates (M = 71.1 %), while reaction time was not affected. Apparently, subjects were sensitive to partner identity and performance, yet variation in motivation rather than assimilation and contrast effects may account for the observed effects.     

Do wild raccoons (Procyon lotor) use tools?

Animal Cognition - Being able to make and use tools was once considered to be an evolutionary hallmark of our species, but has since been documented in other animals. However, for reasons that...     

How do tufted capuchin monkeys (Cebus apella) understand causality involved in tool use?

Four tufted capuchin monkeys (Cebus apella) were trained to choose from 2 hook-like tools, 1 of which successfully led to collecting food, whereas the other did not because of inappropriate spatial arrangement of the tool and the food. In Experiment 1, all of the monkeys successfully learned the basic task. The monkeys performed successfully with tools of novel colors and shapes in Experiments 2-5. These results demonstrate that the monkeys used the spatial arrangement of the tool and the food as a cue. However, they failed when there were obstacles (Experiment 6) or traps (Experiment 7) on the path along which the monkeys dragged tools. These results may suggest that capuchin monkeys understand the spatial relationship between 2 items, namely, food and the tool, but do not understand the spatial relationship among 3 items, namely, food, tool, and the environmental condition. The possible role of stimulus generalization is also considered.     

Do tufted capuchin monkeys (Cebus apella) spontaneously deceive opponents? A preliminary analysis of an experimental food-competition contest between monkeys

A new laboratory procedure which allows the study of deceptive behavior in nonhuman primates is described. Pairs of tufted capuchin monkeys faced each other in a food-competition contest. Two feeder boxes were placed between the monkeys. A piece of food was placed in one of the boxes. The subordinate individual was able to see the food and to open the box to obtain the bait. A dominant male was unable to see the food or to open the box but was able to take the food once the box was opened by the subordinate. In experiment 1, two of four subordinate monkeys spontaneously started to open the unbaited box first with increasing frequency. Experiment 2 confirmed that this "deceptive" act was not due to a drop in the rate of reinforcement caused by the usurping dominant male, under the situation in which food sometimes automatically dropped from the opened box. In experiment 3, two subordinate monkeys were rerun in the same situation as experiment 1. One of them showed some recovery of the "deceptive" act but the other did not; instead the latter tended to position himself on the side where there was no food before he started to open the box. Although the results do not clearly indicate spontaneous deception, we suggest that operationally defined spontaneous deceptive behaviors in monkeys can be analyzed with experimental procedures such as those used here. Accepted after revision: 13 June 2001 Electronic Publication     

I acknowledge your help: capuchin monkeys’ sensitivity to others’ labor

Our society is sustained by wide-ranging cooperation. If individuals are sensitive to others’ gains and losses as well as the amount of labor, they can ensure future beneficial cooperative interaction. However, it is still an open question whether nonhuman primates are sensitive to others’ labor. We asked this question in tufted capuchin monkeys in an experimental food-sharing situation by comparing conditions with labor by two participants equalized (Equal labor condition) or unequalized (Unequal labor condition). The operator monkey pulled the drawer of one of the two food containers placed between two monkeys, each containing a food for him/herself and another for the recipient monkey. The recipient received either high- or low-value food depending on the operator’s choice, whereas the operator obtained the same food regardless of his/her choice. In Unequal labor condition, the operator first had to pull the handle of the board to which the containers were glued and then pull the drawer of one of the containers, while the recipient received food with no labor. In Equal labor condition, the recipient had to pull the handle of the board so that the operator could operate a container. Results showed that operators chose the high-value food container for recipients more often than when the recipient was absent only in Equal labor condition. This suggests that capuchin monkeys are sensitive to others’ labor and actively give food to a partner who has helped them to complete a task.     

Tool use as a way to assess cognition: how do captive chimpanzees handle the weight of the hammer when cracking a nut?

Tool use in apes has been considered a landmark in cognition. However, while most studies concentrate on mental operations, there are very few studies of apes’ cognition as expressed in manual skills. This paper proposes theoretical and methodological considerations on movement analysis as a way of assessing primate cognition. We argue that a privileged way of appraising the characteristics of the cognitive abilities involved in tool use lies at the functional level. This implies that we focus on how the action proceeds, and more precisely, on how the functional characteristics of the task are generated. To support our view, we present the results of an experiment with five captive chimpanzees investigating the way how chimpanzees adapt to hammers of various weights while cracking nuts. The movement performed in the hammering task is analyzed in terms of energy production. Results show that chimpanzees mobilise passive as well as active forces to perform the compliant movement, that is, they modulate the dynamics of the arm/tool system. A comparison between chimpanzees suggests that experience contributes to this skill. The results suggest that in tool use, movements are not key per se, but only in as much as they express underlying cognitive processes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Do great apes use emotional expressions to infer desires?

Although apes understand others’ goals and perceptions, little is known about their understanding of others’ emotional expressions. We conducted three studies following the general paradigm of Repacholi and colleagues (1997, 1998 ). In Study 1, a human reacted emotionally to the hidden contents of two boxes, after which the ape was allowed to choose one of the boxes. Apes distinguished between two of the expressed emotions (happiness and disgust) by choosing appropriately. In Studies 2 and 3, a human reacted either positively or negatively to the hidden contents of two containers; then the ape saw him eating something. When given a choice, apes correctly chose the container to which the human had reacted negatively, based on the inference that the human had just eaten the food to which he had reacted positively – and so the other container still had food left in it. These findings suggest that great apes understand both the directedness and the valence of some human emotional expressions, and can use this understanding to infer desires.     

Do rhesus monkeys (Macaca mulatta) attribute knowledge and ignorance to others?

The ability of 4 rhesus monkeys (Macaca mulatta) to understand the causal connection between seeing and knowing was investigated. The subjects were tested to determine if they could discriminate between information provided by experimenters who randomly alternated between roles of guesser and knower. In a series of tests, the knower either hid food under 1 of 3 cups or watched as someone else hid the food. The guesser waited outside the room or covered her or his head until the food was hidden. The subjects watched this procedure occur but could not see which cup the food was hidden under. The knower pointed to the correct cup while the guesser pointed to an incorrect one. None of the macaques provided any evidence that they realized the different states of knowledge possessed by the guesser and knower. The results are consistent with the hypothesis that rhesus macaques are incapable of making inferences about the mental states of others.     

Do people use language production to make predictions during comprehension?

We present the case that language comprehension involves making simultaneous predictions at different linguistic levels and that these predictions are generated by the language production system. Recent research suggests that ease of comprehending predictable elements is due to prediction rather than facilitated integration, and that comprehension is accompanied by covert imitation. We argue that comprehenders use prediction and imitation to construct an "emulator", using the production system, and combine predictions with the input dynamically. Such a process helps to explain the rapidity of comprehension and the robust interpretation of ambiguous or noisy input. This framework is in line with a general trend in cognitive science to incorporate action systems into perceptual systems and has broad implications for understanding the links between language production and comprehension.     

Do apes and monkeys rely upon conceptual reversibility?

The ability to seriate nesting cups as a sensorimotor task has posed interesting questions for cognitive scientists. Greenfield et al. [(1972) Cognit Psychol 3:291–310] found parallels between children's combinatorial activity with nesting cups and patterns of phonological and grammatical constructions. The parallels suggested the possibility of a neurally based developmental homology between language and instrumental action [Greenfield (1991) Behav Brain Sci 14:531–595]. Children who predominantly used subassembly, a hierarchical method of combining cups, succeeded at seriating nesting cups more often than those who did not. Greenfield and others [e.g., Piaget and Inhelder (1969) The psychology of the child. Basic Books, New York; DeLoache et al. (1985) Child Dev 56:928–939] argued that success in seriation reflects the child's growing recognition of a reversible relationship: a particular element in a series is conceived of as being smaller than the previous element and larger than the subsequent element. But is a concept of reversibility or a hierarchical form of object manipulation necessary to seriate cups? In this article, we review studies with very young children and nonhuman primates to determine how individuals that do not evidence conceptual reversibility manage the seriation task. We argue that the development of skill in seriation is experientially, rather than conceptually, driven and that it may be unnecessary to link seriation with cognitive conceptions of reversibility or linguistic capacities. Rather, in ordering a set of objects by size, perceptual-motor learning may enable contemplative refinement. Accepted after revision: 10 September 2001 Electronic Publication     

Do children use similar processes to read and spell words?

The use of spelling-sound information in both reading and spelling was evaluated by having children read and spell nonwords and five types of words that differed in terms of their regularity for reading and spelling. The subjects were grade 3 children who had been psychometrically defined as good readers and good spellers (“good”), good readers and poor spellers (“mixed”), or poor readers and poor spellers (“poor”). Results indicated that all children attempted to use spelling-sound correspondences in both reading and spelling, although children in both the mixed and the poor groups had weaker knowledge of these correspondences and were less systematic in their use of them. Furthermore, even though the children in the mixed group had been matched with children in the good group on reading comprehension, the number and type of errors made by the mixed subjects on both the reading and spelling tasks were more similar to those of the poor subjects than to those of the good subjects.     

What limits tool use in nonhuman primates? Insights from tufted capuchin monkeys (Sapajus spp.) and chimpanzees (Pan troglodytes) aligning three-dimensional objects to a surface

Perceptuomotor functions that support using hand tools can be examined in other manipulation tasks, such as alignment of objects to surfaces. We examined tufted capuchin monkeys’ and chimpanzees’ performance at aligning objects to surfaces while managing one or two spatial relations to do so. We presented six subjects of each species with a single stick to place into a groove, two sticks of equal length to place into two grooves, or two sticks joined as a T to place into a T-shaped groove. Tufted capuchins and chimpanzees performed equivalently on these tasks, aligning the straight stick to within 22.5° of parallel to the groove in approximately half of their attempts to place it, and taking more attempts to place the T stick than two straight sticks. The findings provide strong evidence that tufted capuchins and chimpanzees do not reliably align even one prominent axial feature of an object to a surface, and that managing two concurrent allocentric spatial relations in an alignment problem is significantly more challenging to them than managing two sequential relations. In contrast, humans from 2 years of age display very different perceptuomotor abilities in a similar task: they align sticks to a groove reliably on each attempt, and they readily manage two allocentric spatial relations concurrently. Limitations in aligning objects and in managing two or more relations at a time significantly constrain how nonhuman primates can use hand tools.     

Do monkeys think in metaphors? Representations of space and time in monkeys and humans

Research on the relationship between the representation of space and time has produced two contrasting proposals. ATOM posits that space and time are represented via a common magnitude system, suggesting a symmetrical relationship between space and time. According to metaphor theory, however, representations of time depend on representations of space asymmetrically. Previous findings in humans have supported metaphor theory. Here, we investigate the relationship between time and space in a nonverbal species, by testing whether non-human primates show space–time interactions consistent with metaphor theory or with ATOM. We tested two rhesus monkeys and 16 adult humans in a nonverbal task that assessed the influence of an irrelevant dimension (time or space) on a relevant dimension (space or time). In humans, spatial extent had a large effect on time judgments whereas time had a small effect on spatial judgments. In monkeys, both spatial and temporal manipulations showed large bi-directional effects on judgments. In contrast to humans, spatial manipulations in monkeys did not produce a larger effect on temporal judgments than the reverse. Thus, consistent with previous findings, human adults showed asymmetrical space–time interactions that were predicted by metaphor theory. In contrast, monkeys showed patterns that were more consistent with ATOM.     

Do people use category-learning judgments to regulate their learning of natural categories?

Although research has established that people can accurately judge how well they have learned categories, no research has examined whether people use their category-learning judgments (CLJs) to regulate their restudy of natural categories. Thus, in five experiments we investigated the relationship between people’s CLJs and selections of categories for restudy. Participants first attempted to learn natural categories (bird families; e.g., finches, grosbeaks, and warblers) so that they could categorize new exemplars on a final test. After this initial study phase, participants made a CLJ for each category and then selected a subset of the categories for restudy. Across experiments, we also manipulated several variables (e.g., selecting either three or nine categories, or obtaining 30% vs. 80% performance on the final test) that were expected to influence restudy selections. However, the manipulations typically had minimal impact. More important, in all experiments we found an unexpected outcome: Some participants tended to select the categories they judged to be most well learned for restudy, and others tended to select those judged to be least well learned. We discovered these qualitative differences in the use of CLJs to make restudy selections by using post-hoc analyses in Experiments 1a and 1b, and hence we sought to (a) replicate them in Experiments 2, 3, and 4 and (b) provide preliminary evidence regarding factors that can (vs. cannot) account for them. Most important, evidence across all of the experiments supported the conclusion that people do use their CLJs to select categories for restudy.     

Redundant food searches by capuchin monkeys (Cebus apella): a failure of metacognition?

This study investigated capuchin monkeys' understanding of their own visual search behavior as a means to gather information. Five monkeys were presented with three tubes that could be visually searched to determine the location of a bait. The bait's visibility was experimentally manipulated, and the monkeys' spontaneous visual searches before tube selection were analyzed. In Experiment 1, three monkeys selected the baited tube significantly above chance; however, the monkeys also searched transparent tubes. In Experiment 2, a bent tube in which food was never visible was introduced. When the bent tube was baited, the monkeys failed to deduce the bait location and responded randomly. They also continued to look into the bent tube despite not gaining any pertinent information from it. The capuchin monkeys' behavior contrasts with the efficient employment of visual search behavior reported in humans, apes and macaques. This difference is consistent with species-related variations in metacognitive abilities, although other explanations are also possible.     

Are monkeys able to plan for future exchange?

Whether or not non-human animals can plan for the future is a hotly debated issue. We investigate this question further and use a planning-to-exchange task to study future planning in the cooperative domain in two species of monkeys: the brown capuchin (Cebus apella) and the Tonkean macaque (Macaca tonkeana). The rationale required subjects to plan for a future opportunity to exchange tokens for food by collecting tokens several minutes in advance. Subjects who successfully planned for the exchange task were expected to select suitable tokens during a collection period (5/10?min), save them for a fixed period of time (20/30?min), then take them into an adjacent compartment and exchange them for food with an experimenter. Monkeys mostly failed to transport tokens when entering the testing compartment; hence, they do not seem able to plan for a future exchange with a human partner. Three subjects did however manage to solve the task several times, albeit at very low rates. They brought the correct version of three possible token types, but rarely transported more than one suitable token at a time. Given that the frequency of token manipulation predicted transport, success might have occurred by chance. This was not the case, however, since in most cases subjects were not already holding the token in their hands before they entered the testing compartment. Instead, these results may reflect subjects' strengths and weaknesses in their time-related comprehension of the task.