Perception of shape from shading in chimpanzees (Pan troglodytes) and humans (Homo sapiens)

The perception of shape from shading was tested in two chimpanzees (Pan troglodytes) and five humans (Homo sapiens), using visual search tasks. Subjects were required to select and touch an odd item (target) from among uniform distractors. Humans found the target faster when shading was vertical than when it was horizontal, consistent with results of previous research. Both chimpanzees showed the opposite pattern: they found the target faster when shading was horizontal. The same difference in response was found in texture segregation tasks. This difference between the species could not be explained by head rotation or head shift parallel to the surface of the monitor. Furthermore, when the shaded shape was changed from a circle to a square, or the shading type was changed from gradual to stepwise, the difference in performance between vertical and horizontal shading disappeared in chimpanzees, but persisted in humans. These results suggest that chimpanzees process shading information in a different way from humans. Received: 20 January 1998 / Accepted after revision: 30 March 1998     

Understanding communicative intentions and semiotic vehicles by children and chimpanzees

Developmental and comparative studies of the ability to understand communicative intentions using object-choice tasks raise questions concerning the semiotic properties of the communicative signals, and the roles of rearing histories, language and familiarity. We adapted a study by Tomasello, Call, and Gluckman (1997), in which a “helper” indicated the location of a hidden reward to children of three ages (18, 24, and 30 months) and to four chimpanzees, by means of one of four cues: Pointing, Marker, Picture and Replica. For the chimpanzees, we controlled for familiarity by using two helpers, one unfamiliar and one highly familiar. Even 18-months performed well on Pointing and Marker, while only the oldest group clearly succeeded with Picture and Replica. Performance did not correlate with scores for the Swedish Early Communicative Development Inventory (SECDI). While there were no positive results for the chimpanzees on the group level, and no effect of familiarity, two chimpanzees succeeded on Pointing and Marker. Results support proposals of a species difference in understanding communicative intentions, but also highlight the need to distinguish these from the complexity of semiotic vehicles and to consider both factors.     

幼儿在联合行动中共同表征能力的发展

为探究幼儿联合行动共同表征能力的发展,实验1通过比较186名3~5岁幼儿在相同任务和不同任务的表现,发现4岁和5岁幼儿在不同任务中的表现比相同任务差;实验2进一步验证幼儿在不同任务中较差的表现源于对自我和同伴的共同表征。结论：3岁幼儿无法在联合任务中同时表征自我和同伴,没有表现出明显的共同表征能力,4岁以上幼儿开始具备稳定的共同表征能力,能够在联合任务中同时表征自己和同伴,由此对自己的行为表现造成干扰。     

高功能孤独症儿童的合作行为

合作行为是一种重要的亲社会行为, 对儿童的社会适应具有重要意义, 而孤独症儿童的典型特征是社会功能存在缺陷, 从而导致合作行为的缺乏。以往研究未能就孤独症儿童在不同合作任务类型中的表现做出区分, 本研究采用经典的囚徒困境博弈和合作性工具任务比较了6~12岁的高功能孤独症儿童和正常发展儿童在不同任务中的合作行为。结果显示高功能孤独症儿童和正常儿童在囚徒困境中的合作行为没有显著差异, 然而, 他们在工具性任务中表现出比正常儿童更低水平的合作行为。这说明高功能孤独症儿童在对认知能力有不同要求的合作任务中的表现不同。     

Social comparison mediates chimpanzees’ responses to loss,not frustration

Why do chimpanzees react when their partner gets a better deal than them? Do they note the inequity or do their responses reflect frustration in response to unattainable rewards? To tease apart inequity and contrast, we tested chimpanzees in a series of conditions that created loss through individual contrast, through inequity, or by both. Chimpanzees were tested in four social and two individual conditions in which they received food rewards in return for exchanging tokens with an experimenter. In conditions designed to create individual contrast, after completing an exchange, the chimpanzees were given a relatively less-preferred reward than the one they were previously shown. The chimpanzees’ willingness to accept the less-preferred rewards was independent of previously offered foods in both the social and individual conditions. In conditions that created frustration through inequity, subjects were given a less-preferred reward than the one received by their partner, but not in relation to the reward they were previously offered. In a social context, females were more likely to refuse to participate when they received a less-preferred reward than their partner (disadvantageous inequity), than when they received a more-preferred reward (advantageous inequity). Specifically, the females’ refusals were typified by refusals to exchange tokens rather than refusals to accept food rewards. Males showed no difference in their responses to inequity or individual contrast. These results support previous evidence that some chimpanzees’ responses to inequity are mediated more strongly by what others receive than by frustration effects.     

Causal knowledge and imitation/emulation switching in chimpanzees (Pan troglodytes) and children (Homo sapiens)

This study explored whether the tendency of chimpanzees and children to use emulation or imitation to solve a tool-using task was a response to the availability of causal information. Young wild-born chimpanzees from an African sanctuary and 3- to 4-year-old children observed a human demonstrator use a tool to retrieve a reward from a puzzle-box. The demonstration involved both causally relevant and irrelevant actions, and the box was presented in each of two conditions: opaque and clear. In the opaque condition, causal information about the effect of the tool inside the box was not available, and hence it was impossible to differentiate between the relevant and irrelevant parts of the demonstration. However, in the clear condition causal information was available, and subjects could potentially determine which actions were necessary. When chimpanzees were presented with the opaque box, they reproduced both the relevant and irrelevant actions, thus imitating the overall structure of the task. When the box was presented in the clear condition they instead ignored the irrelevant actions in favour of a more efficient, emulative technique. These results suggest that emulation is the favoured strategy of chimpanzees when sufficient causal information is available. However, if such information is not available, chimpanzees are prone to employ a more comprehensive copy of an observed action. In contrast to the chimpanzees, children employed imitation to solve the task in both conditions, at the expense of efficiency. We suggest that the difference in performance of chimpanzees and children may be due to a greater susceptibility of children to cultural conventions, perhaps combined with a differential focus on the results, actions and goals of the demonstrator.     

Logical versus Associative Performance on Transitive Reasoning Tasks by Children: Implications for the Status of Animals Performance

Although monkeys, pigeons, rats and chimpanzees all appear to be able to draw transitive inferences, young children fail to do so in some situations. If we take successful performance to be indicative of rationality-as animal researchers sometimes do (Monkeys are rational!McGonigle & Chalmers, 1992)-we have the paradox that animals are, on this criterion, more rational than are school-age children. It is possible, however, to complete 5-term transitive tasks by recruiting associative rather than logical processes; and, indeed, the tasks given to animals not only afford associative solutions but seem to require them (M&C tasks, after McGonigle & Chalmers, 1992). We asked whether 5- to 6-year-old children find a task that naturally affords the application of a logical rule (a B&T task, after Bryant & Trabasso, 1971) easier to perform than an M&C task that does not. The children found the B&T task easiera difference that could not be explained in terms of difference in memory for the premises. This leaves open the possibility that, although children are not restricted to associative strategies when completing 5-term series tasks, animals may be thus restricted.     

Picture naming in young children: a developmental study on interhemispheric collaboration

The aim of the present study was to determine how interhemispheric collaboration and visual attention in basic lexical tasks develop during early childhood. Two- to 6-year-old children were asked to name two different pictures presented simultaneously either one in each visual hemifield (bilateral condition) or both in a single hemifield (either right or left, unilateral condition). In the bilateral condition, children were overall more accurate in naming right visual field than left visual field pictures. This difference was significant for 2- and 3- to 4-year-old children, but not for 5- to 6-year-old children. These results show that the right and left cerebral hemispheres do not develop naming competencies equally well in early childhood. A second analysis, based on the order of report, showed that when 2- and 3- to 4-year-old children named both the left and the right visual field pictures, they named the right visual field picture first. In contrast, at the age of 5-6 years, children named the left visual field picture first and overall naming performance reached a ceiling level. Several interpretations are proposed to explain this shift of visual attention at the age of 5-6 years. In the unilateral condition, no difference was found between naming accuracy in the right and left visual fields, presumably because interhemispheric pathways are functional: visual stimuli presented to the right hemisphere can be processed by the most competent left hemisphere without degradation of information. This result confirms previous findings on the development of interhemispheric collaboration.     

Spatial construction skills of chimpanzees (Pan troglodytes) and young human children (Homo sapiens sapiens)

Spatial construction tasks are basic tests of visual‐spatial processing. Two studies have assessed spatial construction skills in chimpanzees (Pan troglodytes) and young children (Homo sapiens sapiens) with a block modelling task. Study 1a subjects were three young chimpanzees and five adult chimpanzees. Study 1b subjects were 30 human children belonging to five age groups (24, 30, 36, 42, 48 months). Subjects were given three model constructions to reproduce: Line, Cross‐Stack and Arch, which differed in type and number of spatial relations and dimensions, but required comparable configurational understanding. Subjects’ constructions were rated for accuracy. Our results show that: (1) chimpanzees are relatively advanced in constructing in the vertical dimension; (2) Among chimpanzees only adults make accurate copies of constructions; (3) Chimpanzees do not develop in the direction of constructing in two dimensions as human children do starting from age 30 months. The pattern of development of construction skills in chimpanzees partially diverges from that of human children and indicates that spatial analysis and spatial representation are partially different in the two species.     

Chimpanzees help others with what they want; children help them with what they need

Humans, including young children, are strongly motivated to help others, even paying a cost to do so. Humans’ nearest primate relatives, great apes, are likewise motivated to help others, raising the question of whether the motivations of humans and apes are the same. Here we compared the underlying motivation to help in human children and chimpanzees. Both species understood the situation and helped a conspecific in a straightforward situation. However, when helpers knew that what the other was requesting would not actually help her, only children gave her what she needed instead of giving her what she requested. These results suggest that both chimpanzees and human children help others but the underlying motivation for why they help differs. In comparison to chimpanzees, young children help in a paternalistic manner. The evolutionary hypothesis is that uniquely human socio‐ecologies based on interdependent cooperation gave rise to uniquely human prosocial motivations to help others paternalistically.     

Delaying gratification for food and tokens in capuchin monkeys (Cebus apella) and chimpanzees (Pan troglodytes): when quantity is salient, symbolic stimuli do not improve performance

Capuchin monkeys have been tested for the capacity to delay gratification for accumulating rewards in recent studies and have exhibited variable results. Meanwhile, chimpanzees have consistently excelled at this task. However, neither species have ever been tested at accumulating symbolic tokens instead of food items, even though previous reports indicate that tokens sometimes facilitate performance in other self-control tasks. Thus, in the present study, we tested capuchin monkeys and chimpanzees for their capacity to delay gratification in a delay maintenance task, in which an experimenter presented items, one at a time, to within reach of an animal for as long as the animal refrained from taking them. In Experiment 1, we assessed how long capuchin monkeys could accumulate items in the delay maintenance task when items were food rewards or tokens exchangeable for food rewards. Monkeys accumulated more food rewards than they did tokens. In Experiment 2, we tested capuchin monkeys and chimpanzees in a similar accumulation test. Whereas capuchins again accumulated more food than tokens, all chimpanzees but one showed no difference in performance in the two conditions. These findings provide additional evidence that chimpanzees exhibit greater self-control capacity in this task than do capuchin monkeys and indicate that symbolic stimuli fail to facilitate delay maintenance when they do not abstract away from the quantitative dimension of the task. This is consistent with previous findings on the effects of symbols on self-control and illuminates what makes accumulation a particularly challenging task.     

Uniquely human self‐control begins at school age

Human beings have remarkable skills of self‐control, but the evolutionary origins of these skills are unknown. Here we compare children at 3 and 6 years of age with one of humans’ two nearest relatives, chimpanzees, on a battery of reactivity and self‐control tasks. Three‐year‐old children and chimpanzees were very similar in their abilities to resist an impulse for immediate gratification, repeat a previously successful action, attend to a distracting noise, and quit in the face of repeated failure. Six‐year‐old children were more skillful than either 3‐year‐olds or chimpanzees at controlling their impulses. These results suggest that humans’ most fundamental skills of self‐control – as part of the overall decision‐making process – are a part of their general great ape heritage, and that their species‐unique skills of self‐control begin at around the age at which many children begin formal schooling.     

Carryover effect of joint attention to repeated events in chimpanzees and young children

Gaze following is a fundamental component of triadic social interaction which includes events and an object shared with other individuals and is found in both human and nonhuman primates. Most previous work has focused only on the immediate reaction after following another’s gaze. In contrast, this study investigated whether gaze following is retained after the observation of the other’s gaze shift, whether this retainment differs between species and age groups, and whether the retainment depends on the nature of the preceding events. In the social condition, subjects (1- and 2-year-old human children and chimpanzees) witnessed an experimenter who looked and pointed in the direction of a target lamp. In the physical condition, the target lamp blinked but the experimenter did not provide any cues. After a brief delay, we presented the same stimulus again without any cues. All subjects looked again to the target location after experiencing the social condition and thus showed a carryover effect. However, only 2-year-olds showed a carryover effect in the physical condition; 1-year-olds and chimpanzees did not. Additionally, only human children showed spontaneous interactive actions such as pointing. Our results suggest that the difference between the two age groups and chimpanzees is conceptual and not only quantitative.     

“Going episodic”: collaborative inhibition and facilitation when long-married couples remember together

Two complementary approaches to the study of collaborative remembering have produced contrasting results. In the experimental “collaborative recall” approach within cognitive psychology, collaborative remembering typically results in “collaborative inhibition”: laboratory groups recall fewer items than their estimated potential. In the cognitive ageing approach, collaborative remembering with a partner or spouse may provide cueing and support to benefit older adults’ performance on everyday memory tasks. To combine the value of experimental and cognitive ageing approaches, we tested the effects of collaborative remembering in older, long-married couples who recalled a non-personal word list and a personal semantic list of shared trips. We scored amount recalled as well as the kinds of details remembered. We found evidence for collaborative inhibition across both tasks when scored strictly as number of list items recalled. However, we found collaborative facilitation of specific episodic details on the personal semantic list, details which were not strictly required for the completion of the task. In fact, there was a trade-off between recall of specific episodic details and number of trips recalled during collaboration. We discuss these results in terms of the functions of shared remembering and what constitutes memory success, particularly for intimate groups and for older adults.     

Multimodal communication by captive chimpanzees (Pan troglodytes)

Many studies have shown that apes and monkeys are adept at cross-modal matching tasks requiring the subject to identify objects in one modality when information regarding those objects has been presented in a different modality. However, much less is known about non-human primates’ production of multimodal signaling in communicative contexts. Here, we present evidence from a study of 110 chimpanzees demonstrating that they select the modality of communication in accordance with variations in the attentional focus of a human interactant, which is consistent with previous research. In each trial, we presented desirable food to one of two chimpanzees, turning mid-way through the trial from facing one chimpanzee to facing the other chimpanzee, and documented their communicative displays, as the experimenter turned towards or away from the subjects. These chimpanzees varied their signals within a context-appropriate modality, displaying a range of different visual signals when a human experimenter was facing them and a range of different auditory or tactile (attention-getting) signals when the human was facing away from them; this finding extends previous research on multimodal signaling in this species. Thus, in the impoverished circumstances characteristic of captivity, complex signaling tactics are nevertheless exhibited by chimpanzees, suggesting continuity in intersubjective psychological processes in humans and apes.     

Raking it in: the impact of enculturation on chimpanzee tool use

Recent evidence for different tool kits, proposed to be based upon culture-like transmission, have been observed across different chimpanzee communities across Western Africa. In light of these findings, the reported failures by seven captive juvenile chimpanzees tested with 27 tool use tasks (Povinelli 2000) seem enigmatic. Here we report successful performance by a group of nine captive, enculturated chimpanzees, and limited success by a group of six semi-enculturated chimpanzees, on two of the Povinelli tasks, the Flimsy Tool task, and the Hybrid Tool task. All chimpanzees were presented with a rake with a flimsy head and a second rake with a rigid head, either of which could be used to attempt to retrieve a food reward that was out of reach. The rigid rake was constructed such that it had the necessary functional features to permit successful retrieval, while the flimsy rake did not. Both chimpanzee groups in the present experiment selected the functional rigid tool correctly to use during the Flimsy Tool task. All animals were then presented with two “hybrid rakes” A and B, with one half of each rake head constructed from flimsy, non-functional fabric, and the other half of the head was made of wood. Food rewards were placed in front of the rigid side of Rake A and the flimsy side of Rake B. To be successful, the chimps needed to choose the rake that had the reward in front of the rigid side of the rake head. The fully enculturated animals were successful in selecting the functional rake, while the semi-enculturated subjects chose randomly between the two hybrid tools. Compared with findings from Povinelli, whose non-enculturated animals failed both tasks, our results demonstrate that chimpanzees reared under conditions of semi-enculturation could learn to discriminate correctly the necessary tool through trial-and-error during the Flimsy Tool task, but were unable to recognize the functional relationship necessary for retrieving the reward with the “hybrid” rake. In contrast, the enculturated chimpanzees were correct in their choices during both the Flimsy Tool and the Hybrid Tool tasks. These results provide the first empirical evidence for the differential effects of enculturation on subsequent tool use capacities in captive chimpanzees.     

Tracking the displacement of objects: a series of tasks with great apes (Pan troglodytes, Pan paniscus, Gorilla gorilla, and Pongo pygmaeus) and young children (Homo sapiens)

The authors administered a series of object displacement tasks to 24 great apes and 24 30-month-old children (Homo sapiens). Objects were placed under 1 or 2 of 3 cups by visible or invisible displacements. The series included 6 tasks: delayed response, inhibition test, A not B, rotations, transpositions, and object permanence. Apes and children solved most tasks performing at comparable levels except in the transposition task, in which apes performed better than children. Ape species performed at comparable levels in all tasks except in single transpositions, in which chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) performed better than gorillas (Gorilla gorilla) and orangutans (Pongo pygmeaus). All species found nonadjacent trials and rotations especially difficult. The number of elements that changed locations, the type of displacement, and having to inhibit predominant reaching responses were factors that negatively affected the subjects' performance.     

Discrimination of contour-deleted images in baboons (<Emphasis Type="Italic">Papio papio</Emphasis>) and chimpanzees (<Emphasis Type="Italic">Pan troglodytes</Emphasis>)

Humans readily group component elements into a coherent perceptual whole and perceive the global form of visual patterns in priority over local features, which stands in contrast to at least some data from the animal literature, suggesting possible species differences in perceptual processes. In this study, chimpanzees and baboons were required to match intact and partially contour-deleted line-drawings in a computerized task in order to further explore the ability of nonhuman primates to group component elements into a coherent perceptual whole and to determine to what extent they use the global form or the local features. Experiment 1 showed that the baboons and chimpanzees matched intact continuous line-drawings (intact-intact) more easily than partially contour-deleted line-drawings (deleted-deleted). Both species could also match partially deleted line-drawings with their intact version (deleted-intact), but at a lower performance level. Experiment 2 further showed that subjects from the two species could match partially deleted coherent line-drawings (deleted-deleted) more easily than their scrambled incoherent versions (scrambled-scrambled). They could however match the coherent deleted forms with their scrambled version (deleted-scrambled). It is suggested that solutions of these tasks rely on the processing of both global and local cues, with no clear-cut species difference in that ability. Overall, the results show that contour completion of line-drawings was not easy. Implications on the processing of human-made two-dimensional representations such as line-drawings are discussed.     

Species difference in the timing of gaze movement between chimpanzees and humans

How do humans and their closest relatives, chimpanzees, differ in their fundamental abilities for seeing the visual world? In this study, we directly compared the gaze movements of humans and the closest species, chimpanzees, using an eye-tracking system. During free viewing of a naturalistic scene, chimpanzees made more fixations per second (up to four) than did humans (up to three). This species difference was independent of the semantic variability of the presented scenes. The gap–overlap paradigm revealed that, rather than resulting from the sensitivity to the peripherally presented stimuli per se, the species difference reflected the particular strategy each species employed to solve the rivalry between central (fixated) and peripheral stimuli in their visual fields. Finally, when presented with a movie in which small images successively appeared/disappeared at random positions at the chosen presentation rate, chimpanzees tracked those images at the point of fixation for a longer time than did humans, outperforming humans in their speed of scanning. Our results suggest that chimpanzees and humans differ quantitatively in their visual strategies involving the timing of gaze movement. We discuss the functional reasons for each species’ employing such specific strategies.     

Quantity judgments of auditory and visual stimuli by chimpanzees (Pan troglodytes)

Many species can choose between two visual sets of stimuli on the basis of quantity. This is true when sets are both visible, or are presented one set at a time or even one item at a time. However, we know comparatively little about how well nonhuman animals can compare auditory quantities. Here, three chimpanzees (Pan troglodytes) chose between two sets of food items when they only heard each item fall into different containers rather than seeing those items. This method prevented the chimpanzees from summing the amount of visible food they saw because there were no visual cues. Chimpanzees performed well, and their performance matched that of previous experiments with regard to obeying Weber's law. They also performed well with comparisons between a sequentially presented auditory set and a fully visible set, demonstrating that duration of presentation was not being used as a cue. In addition, they accommodated empty sets into these judgments, although not perfectly. Thus, chimpanzees can judge auditory quantities in flexible ways that show many similarities to how they compare visual quantities.