Self-control and tool use in tufted capuchin monkeys (Cebus apella).

Self-control is defined as forgoing immediate gratification to obtain a greater reward. Tool use may relate to self-control because both behaviors may require foresight and deliberate control over one's actions. The authors assessed 20 capuchin monkeys (Cebus apella) for the ability to delay gratification in a tool task. Subjects were given rod-shaped food items that could either be consumed immediately or be carried to an apparatus and used to extract a more preferred food. The authors found that some monkeys were able to exhibit self-control. Monkeys with relatively more tool use experience demonstrated the greatest levels of self-control. These results indicate that capuchins are capable of delaying gratification when a higher quality reinforcer is present and that tool experience can influence levels of self-control in this task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditional copying fidelity in capuchin monkeys (Cebus apella).

In the last two decades, it became largely accepted that monkeys show little, if any, copying fidelity. However, some recent studies have begun to challenge this notion. To explore reasons for such contrary findings, we designed a foraging apparatus so that in each of two experiments with capuchin monkeys (Cebus apella), a model would demonstrate one of two alternative methods to obtain food. The apparatus had a V-shaped track on which a panel could be slid up left or right from the center to reveal food. In Experiment 1, food was located in a cup directly behind the center panel. In Experiment 2, sliding the panel left or right revealed food either in left or right ends of the V-track. Since this sliding movement led directly to one food location exclusive of the other, we predicted capuchins would show greater copying fidelity in this second Experiment. Instead, subjects were significantly more faithful to the model’s method in Experiment 1, which provided strong evidence of capuchins copying what they had observed. We suggest that the contrasting results of Experiment 1 may have occurred because capuchins prioritize exploratory behavior when alternative foraging locations are accessible. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Primary motor cortex asymmetry is correlated with handedness in capuchin monkeys (cebus apella).

Humans exhibit a population-wide tendency toward right-handedness, and structural asymmetries of the primary motor cortex are associated with hand preference. Reported are similar asymmetries correlated with hand preference in a New World monkey (Cebus apella) that does not display population-level handedness. Asymmetry of central sulcus depth is significantly different between left-handed and right-handed individuals as determined by a coordinated bimanual task. Left-handed individuals have a deeper central sulcus in the contralateral hemisphere; right-handed individuals have a more symmetrical central sulcus depth. Cerebral hemispheric specialization for hand preference is not uniquely human and may be more common among primates in general. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of skilled detection and extraction of embedded prey by wild brown capuchin monkeys (cebus apella apella).

Brown capuchin monkeys (Cebus apella apella) in Suriname forage on larvae enclosed within healthy bamboo stalks. We applied the searching versus handling dichotomy of optimal foraging models to highlight developmental processes contributing to foraging on embedded prey. Larvae acquisition begins with search; selecting an appropriate stalk and locating the embedded larvae; followed by handling, ripping the stalk open, and extracting the larvae. Although extraction behaviors were present at low rates in infant capuchins' repertoire, we found that the acquisition of adequate detection techniques was fully completed in subadults, aged around 6. Selecting appropriate foraging substrates, requiring accurate assessment of the physical properties of bamboo stalks, gradually increased with age and experience. We showed that both components of searching required extended practice beyond that required to master the handling components. We conclude that the developmental sequence of skill acquisition goes counter to the preceding logical sequence of foraging process and suggest that searching components present greater challenges than handling components in extractive foraging. Specifying the searching components of foraging more precisely will enhance understanding of species variation in the developmental schedule of foraging skills. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning and generalization of tool use by tufted capuchin monkeys (Cebus apella) in tasks involving three factors: Reward, tool, and hindrance.

We tested 4 captive tufted capuchin monkeys (Cebus apella) for their understanding of physical causality in variations of a 2-choice tool use task, 1 alternative of which allowed the monkeys easier access to food. Our monkeys, who had been adept at this task involving 2 items, that is, tool and food, quickly learned 3-term problems involving food, tool, and 1 type of hindrance (an obstacle or a trap, which could prevent success). All of the monkeys generalized their performance to new problems with the other type of hindrance and those with another familiar tool. These results suggest flexibility of their abilities to process complex physical information comprising 3 items in the environment, that is food–tool–hindrance spatial relationships. Such flexibility also implies that capuchin monkeys may possess rudimentary understanding of causal relationships involved in tool use. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The relative use of proximity, shape similarity, and orientation as visual perceptual grouping cues in tufted capuchin monkeys (Cebus apella) and humans (Homo sapiens).

Recent experimental results suggest that human and nonhuman primates differ in how they process visual information to assemble component parts into global shapes. To assess whether some of the observed differences in perceptual grouping could be accounted for by the prevalence of different grouping factors in different species, we carried out 2 experiments designed to evaluate the relative use of proximity, similarity of shape, and orientation as grouping cues in humans (Homo sapiens) and capuchin monkeys (Cebus apella). Both species showed similarly high levels of accuracy using proximity as a cue. Moreover, for both species, grouping by orientation similarity produced a lower level of performance than grouping by proximity. Differences emerged with respect to the use of shape similarity as a cue. In humans, grouping by shape similarity also proved less effective than grouping by proximity but the same was not observed in capuchins. These results suggest that there may be subtle differences between humans and capuchin monkeys in the weighting assigned to different grouping cues that may affect the way in which they combine local features into global shapes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Auditory-visual cross-modal perception of communicative stimuli in Tufted Capuchin Monkeys (Cebus apella).

Research on cross-modal performance in nonhuman primates is limited to a small number of sensory modalities and testing methods. To broaden the scope of this research, the authors tested capuchin monkeys (Cebus apella) for a seldom-studied cross-modal capacity in nonhuman primates, auditory-visual recognition. Monkeys were simultaneously played 2 video recordings of a face producing different vocalizations and a sound recording of 1 of the vocalizations. Stimulus sets varied from naturally occurring conspecific vocalizations to experimentally controlled human speech stimuli. The authors found that monkeys preferred to view face recordings that matched presented vocal stimuli. Their preference did not differ significantly across stimulus species or other stimulus features. However, the reliability of the latter set of results may have been limited by sample size. From these results, the authors concluded that capuchin monkeys exhibit auditory-visual cross-modal perception of conspecific vocalizations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

How capuchin monkeys (Cebus apella) quantify objects and substances.

Humans and nonhuman animals appear to share a capacity for nonverbal quantity representations. But what are the limits of these abilities? Results of previous research with human infants suggest that the ontological status of an entity as an object or a substance affects infants' ability to quantify it. We ask whether the same is true for another primate species-the New World monkey Cebus apella. We tested capuchin monkeys' ability to select the greater of two quantities of either discrete objects or a nonsolid substance. Participants performed above chance with both objects (Experiment 1) and substances (Experiment 2); in both cases, the observed performance was ratio dependent. This finding suggests that capuchins quantify objects and substances similarly and do so via analog magnitude representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Quality before quantity: Rapid learning of reverse-reward contingency by capuchin monkeys (Cebus apella).

Capuchin monkeys (Cebus apella) were tested on a reverse-reward task involving different quantities of the same food, or an identical quantity of different foods. All monkeys tested first on the qualitative version spontaneously mastered the task, whereas only one of four spontaneously mastered the quantitative version. No monkey reached criterion when the tasks were switched, although almost all did so following remedial procedures after the study. The results suggest that (a) qualitative reverse-reward is easier than quantitative versions of the problem, (b) quality and quantity dimensions are processed differently in food-related tasks, and (c) capuchin monkeys can show rapid and spontaneous learning of reverse-reward contingencies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Delay of gratification in capuchin monkeys (cebus apella) and squirrel monkeys (saimiri sciureus).

In two separate series of experiments four capuchin monkeys (Cebus apella) and four squirrel monkeys (Saimiri sciureus) were given demonstration trials in which a human transferred six pieces of food, one by one, from out of each monkey's reach to within reach. On test trials the monkey could reach for the transferred food at any time, an action that ended the trial. Therefore, it was in the monkey's interest to allow food items to accumulate before reaching for food. No capuchin monkey showed delay of gratification in the first phase of testing. An attempt to facilitate performance by presenting a single free food item immediately before the transfer failed (Phase 2). In Phase 3, when the transferred food items increased progressively in size, two capuchins maintained delays, and frequently waited for all 6 items to accumulate. One squirrel monkey started to delay gratification in Phase 1, and another did so in Phase 3. A return to single-sized food items did not impair the monkeys' ability to delay. Short (1 s) interitem delays were generally easier to maintain than longer delays (3 or 5 s). In both species the delaying individuals bridged the delays idiosyncratically. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inferences about the location of food in capuchin monkeys (Cebus apella) in two sensory modalities.

The authors tested the ability of capuchin monkeys (Cebus apella) to make inferences about hidden food. In Experiment 1, we showed the content of 2 boxes, 1 of which was baited (visual condition, VC) or we shook both boxes producing noise from the baited box (auditory condition, AC). Seven subjects (out of 8) were above chance in the VC, whereas only 1 was above chance in AC. During treatment, by manipulating empty and filled objects subjects experienced the relation between noise and content. When tested again, 7 capuchins were above chance in the VC and 3 in AC. In Experiment 2, we gave visual or auditory information only about the empty box and, consequently, successful choice implied inferential reasoning. All subjects (out of 4) were above chance in the VC, and 2 in the AC. Control tests ruled out the possibility that success resulted from simply avoiding the shaken noiseless box, or from the use of arbitrary auditory information. Similar to apes (Call, 2004), capuchins were capable of inferential reasoning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ordinal judgments of symbolic stimuli by capuchin monkeys (Cebus apella) and rhesus monkeys (Macaca mulatta): The effects of differential and nondifferential reward.

Ordinal learning was investigated in capuchin monkeys (Cebus apella) and rhesus monkeys (Macaca mulatta). In Experiment 1, both species were presented with pairings of the Arabic numerals 0 to 9. Some monkeys were given food rewards equal to the value of the numeral selected and some were rewarded with a single pellet only for choosing the higher numeral within the pair. Both species learned to select the larger numeral, but only rhesus monkeys that were differentially rewarded performed above chance levels when presented with novel probe pairings. In Experiment 2, the monkeys were first presented with arrays of 5 familiar numerals (from the range 0 to 9) and then arrays of 5 novel letters (from the range A to J) with the same reward outcomes in place as in Experiment 1. Both species performed better with the numerals, suggesting that an ordinal sequence of all stimuli had been learned during Experiment 1, rather than a matrix of two-choice discriminations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Monkeys (Macaca mulatta and Cebus apella) track, enumerate, and compare multiple sets of moving items.

Despite many demonstrations of numerical competence in nonhuman animals, little is known about how well animals enumerate moving stimuli. In this series of experiments, rhesus monkeys (Macaca mulatta) and capuchin monkeys (Cebus apella) performed computerized tasks in which they had to enumerate sets of stimuli. In Experiment 1, rhesus monkeys compared two sets of moving stimuli. Experiment 2 required comparisons of a moving set and a static set. Experiment 3 included human participants and capuchin monkeys to assess all 3 species' performance and to determine whether responding was to the numerical properties of the stimulus sets rather than to some other stimulus property such as cumulative area. Experiment 4 required both monkey species to enumerate subsets of each moving array. In all experiments, monkeys performed above chance levels, and their responses were controlled by the number of items in the arrays as opposed to nonnumerical stimulus dimensions. Rhesus monkeys performed comparably to adult humans when directly compared although capuchin performance was lower. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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 she 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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Face recognition in capuchin monkeys (Cebus apella).

Primates live in complex social groups that necessitate recognition of the individuals with whom they interact. In humans, faces provide a visual means by which to gain information such as identity, allowing us to distinguish between both familiar and unfamiliar individuals. The current study used a computerized oddity task to investigate whether a New World primate, Cebus apella, can discriminate the faces of In-group and Out-group conspecifics based on identity. The current study, improved on past methodologies, demonstrates that capuchins recognize the faces of both familiar and unfamiliar conspecifics. Once a performance criterion had been reached, subjects successfully transferred to a large number of novel images within the first 100 trials thus ruling out performance based on previous conditioning. Capuchins can be added to a growing list of primates that appear to recognize two-dimensional facial images of conspecifics. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cooperative problem solving by tufted capuchin monkeys (Cebus apella): Spontaneous division of labor, communication, and reciprocal altruism.

Using an experimentally induced cooperation task, the authors investigated whether tufted capuchin monkeys (Cebus apella) share the following 3 characteristics of cooperation with humans: division of labor, communication, and reciprocal altruism. In Experiment 1, the authors trained individual monkeys to perform the necessary sequence of actions for rewards and tested them in pairs to assess whether they could solve the task by spontaneously dividing the sequence of actions. All pairs solved this task. In Experiment 2, monkeys worked in the cooperation task and a task requiring no partner help. They looked at the partner significantly longer in the former task than in the latter, but communicative intent could not be determined. In Experiment 3, only 1 of 2 participants obtained a reward on each trial. Monkeys maintained cooperation when their roles were reversed on alternate trials. Their cooperative performances demonstrated division of labor; results suggest task-related communication and reciprocal altruism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Experience and Materials Affect Combinatorial Construction in Tufted Capuchin Monkeys (Cebus apella).

Three movement procedures can combine nesting cups into seriated structures. Reliance on these procedures changes with age in human children, and the putatively most advanced emerges as a predominant procedure at 3 or more years. Six monkeys' (Cebus apella) combinatorial procedures and successes at nesting seriated cups were evaluated. The current study examined whether the procedures used (a) shift toward more efficient procedures after unguided experience, (b) are dependent on the type of object being combined, and (c) can be altered by specific training history. All factors produced a change in procedure for some individuals, suggesting that combinatorial procedure is a product of the dynamic influences of preexisting tendencies to act in certain ways, of environmental circumstances, and of prior experiences. Some monkeys preferred the putatively most cognitively complex procedure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attention allocation modulates the processing of hierarchical visual patterns: A comparative analysis of capuchin monkeys (Cebus apella) and humans.

Humans show a global advantage when processing hierarchical visual patterns, and they detect the global level of stimulus structure more accurately and faster than the local level in several stimulus contexts. By contrast, capuchins (Cebus apella) and other monkey species show a strong local advantage. A key factor which, if manipulated, could cause an inversion of this effect in monkeys is still to be found. In this study, we examined whether it was possible to induce attention allocation to global and local levels of perceptual analysis in capuchin monkeys and if by doing so, their local dominance could be reversed. We manipulated attentional bias using a matching-to-sample (MTS) task where the proportion of trials requiring global and local processing varied between conditions. The monkeys were compared with humans tested with the same paradigm. Monkeys showed a local advantage in the local bias condition but a global advantage in the global bias condition. The role of attention in processing was confined to the local trials in a first phase of testing but extended to both local and global trials in the course of task practice. Humans exhibited an overall global dominance and an effect of attentional bias on the speed of processing of the global and local level of the stimuli. These results indicate a role for attention in the processing of hierarchical stimuli in monkeys and are discussed in relation to the extent to which they can explain the differences between capuchin monkeys and humans observed in this and other studies. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Visual list memory in capuchin monkeys (Cebus apella).

Memory of 3 capuchin monkeys, Cebus apella, was tested with lists of 4 travel-slide pictures and different retention intervals. They touched different areas of a video monitor to indicate whether a test picture was in a list. At short retention intervals (0 s, 1 s, 2 s), memory was good for the last list items (recency effect). At a 10-s retention interval, memory improved for 1st list items (primacy effect). At long retention intervals (20 s and 30 s), primacy effects were strong and recency effects had dissipated. The pattern of retention-interval changes was similar to rhesus monkeys, humans, and pigeons. The time course of recency dissipation was similar to rhesus monkeys. The capuchin's superior tool-use ability was discussed in relation to whether it reflects a superior general cognitive ability, such as memory. In terms of visual memory, capuchin monkeys were not shown to be superior to rhesus monkeys. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Choosing and Using Tools: Capuchins (Cebus apella) Use a Different Metric Than Tamarins (Saguinus oedipus).

Cotton-top tamarins (Saguinus oedipus) selected canes positioned so that a straight inward pull brought food within reach (M. D. Hauser, 1997; see also record 1997-41347-003). Tamarins failed to retrieve food with canes in other positions, and they did not reposition these canes. In this study, tufted capuchin monkeys (Cebus apella) preferred canes they could pull straight in when these were present, but they also repositioned canes in individually variable ways, and their success at obtaining food with repositioned canes improved with practice. In accord with predictions drawn from ecological psychology, capuchins discovered affordances of canes through exploratory actions with these objects, whereas tamarins did not. Ecological theory predicts these differences on the basis of species-typical manipulative activity, and it provides a useful approach for the study of species differences in tool-using behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)