An obedient orangutan (Pongo abelii) performs perfectly in peripheral object-choice tasks but fails the standard centrally presented versions.

Mulcahy and Call (2009) found that bonobos (Pan paniscus) and chimpanzees (Pan troglodytes) but not orangutans (Pongo pygmaeus) perform significantly better in a peripheral version of the object-choice task compared to the original central version. Orangutans may have failed because they avoided direct eye contact with the experimenter when the cue was given. We investigated this possibility by conducting peripheral and central object choice tasks with an obedient orangutan (Pongo abelii) whom the experimenter could elicit eye contact with in each trial. In contrast to Mulcahy and Call's findings, the subject only failed the object choice task when tested with the central and not the peripheral version. We investigated whether success was because of the greater distance the subject was required to move in order to make a choice in peripheral trials. Results show that this was an unlikely factor in the subject's success. We discuss our findings in relation to previous and future object-choice research. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Learning and limits of use of eye gaze by capuchin monkeys (Cebus apella) in an object-choice task.

The ability of 3 capuchin monkeys (Cebus apella) to use experimenter-given cues to solve an object-choice task was assessed. The monkeys learned to use explicit gestural and postural cues and then progressed to using eye-gaze-only cues to solve the task, that is, to choose the baited 1 of 2 objects and thus obtain a food reward. Increasing cue-stimulus distance and introducing movement of the eyes impeded the establishment of effective eye-gaze reading. One monkey showed positive but imperfect transfer of use of eye gaze when a novel experimenter presented the cue. When head and eye orientation cues were presented simultaneously and in conflict, the monkeys showed greater responsiveness to head orientation cues. The results show that capuchin monkeys can learn to use eye gaze as a discriminative cue, but there was no evidence for any underlying awareness of eye gaze as a cue to direction of attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Token transfers among great apes (Gorilla gorilla, Pongo pygmaeus, Pan paniscus, and Pan troglodytes): Species differences, gestural requests, and reciprocal exchange.

Great apes appear to be the nonhuman primates most capable of recognizing trading opportunities and engaging in transfers of commodities with conspecifics. Spontaneous exchange of goods between them has not yet been reported. We tested gorillas (Gorilla gorilla), orangutans (Pongo pygmaeus), bonobos (Pan paniscus), and chimpanzees (Pan troglodytes) in a token-exchange task involving two conspecifics and a human experimenter. Tested in pairs, subjects had to exchange tokens with a partner to obtain food from the experimenter. We observed 4, 5, 264, and 328 transfers of tokens in gorillas, chimpanzees, orangutans, and bonobos, respectively. Most gifts were indirect in gorillas, chimpanzees, and bonobos, whereas most were direct in orangutans. The analysis showed no evidence of calculated reciprocity in interactions. A main finding of the study was the high rate of repeated gifts and begging gestures recorded in orangutans. This raises the question of the meaning of pointing in great apes and their ability to understand the communicative intent of others. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Use of human visual attention cues by olive baboons (Papio anubis) in a competitive task.

The ability of 4 olive baboons (Papio anubis) to use human gaze cues during a competitive food task was investigated. Three baboons used head orientation as a cue, and 1 individual also used eye direction alone. As the baboons did not receive prior training with gestural cuts, their performance suggests that the competitive paradigm may be more appropriate for testing nonhuman primates than the standard object-choice paradigm. However, the baboons were insensitive to whether the experimenter could actually perceive the food item, and therefore the use of visual orientation cues may not be indicative of visual perspective-taking abilities. Performance was disrupted by the introduction of a screen and objects to conceal food items and by the absence of movement in cues presented. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The performance of bonobos (Pan paniscus), chimpanzees (Pan troglodytes), and orangutans (Pongo pygmaeus) in two versions of an object-choice task.

The object-choice task tests animals’ ability to use human-given cues to find a hidden reward located in 1 of 2 (or more) containers. Great apes are generally unskillful in this task whereas other species including dogs (Canis familiaris) and goats (Capra hircus) can use human-given cues to locate the reward. However, great apes are typically positioned proximal to the containers when receiving the experimenter’s cue whereas other species are invariably positioned distally. The authors investigated how the position of the subject, the human giving the cue and the containers (and the distance among them) affected the performance of 19 captive great apes. Compared to the proximal condition, the distal condition involved larger distances and, critically, it reduced the potential ambiguity of the cues as well as the strong influence that the sight of the containers may have had when subjects received the cue. Subjects were far more successful in the distal compared to the proximal condition. The authors suggest several possibilities to account for this difference and discuss our findings in relation to previous and future object-choice research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gorillas (Gorilla gorilla) and Orangutans (Pongo pygmaeus) Encode Relevant Problem Features in a Tool-Using Task.

Two important elements in problem solving are the abilities to encode relevant task features and to combine multiple actions to achieve the goal. The authors investigated these 2 elements in a task in which gorillas (Gorilla gorilla) and orangutans (Pongo pygmaeus) had to use a tool to retrieve an out-of-reach reward. Subjects were able to select tools of an appropriate length to reach the reward even when the position of the reward and tools were not simultaneously visible. When presented with tools that were too short to retrieve the reward, subjects were more likely to refuse to use them than when tools were the appropriate length. Subjects were proficient at using tools in sequence to retrieve the reward. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hand preference for food processing in wild western lowland gorillas (gorilla gorilla gorilla).

Western lowland gorillas (Gorilla gorilla gorilla) have not previously been represented in studies of laterality in wild great apes. The discovery of swampy clearings frequented by gorillas in northern Congo has provided the first opportunity to redress this imbalance. Hand preference data are presented from 33 gorillas in seated and standing postures, covering the procurement and processing of 2 to 4 plant species. Levels of hand preference exhibited were low. When data from all postures and plant species were pooled, 33% of gorillas showed hand preferences in excess of chance. In the standing posture, more gorillas exhibited significant left-hand preferences than right, but an overall population-level bias was not evident. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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

Attentional capture of objects referred to by spoken language.

Participants saw a small number of objects in a visual display and performed a visual detection or visual-discrimination task in the context of task-irrelevant spoken distractors. In each experiment, a visual cue was presented 400 ms after the onset of a spoken word. In experiments 1 and 2, the cue was an isoluminant color change and participants generated an eye movement to the target object. In experiment 1, responses were slower when the spoken word referred to the distractor object than when it referred to the target object. In experiment 2, responses were slower when the spoken word referred to a distractor object than when it referred to an object not in the display. In experiment 3, the cue was a small shift in location of the target object and participants indicated the direction of the shift. Responses were slowest when the word referred to the distractor object, faster when the word did not have a referent, and fastest when the word referred to the target object. Taken together, the results demonstrate that referents of spoken words capture attention. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Gorillas' (Gorilla gorilla gorilla) spatial memory in a foraging task.

The spatial memory of 2 gorillas (Gorilla gorilla gorilla) was explored in a simulated foraging task. Trials consisted of 2 parts separated by a delay. In the 1st part, half of the total number of food sites were baited with a highly preferred food, and the subject was allowed to search, find, and consume these items (search phase). During the delay the same locations were again baited. After the delay the animal was reintroduced to the test enclosure and allowed to search through the sites again (re-search phase). In Exp 1, an adult gorilla was very accurate in remembering locations that had previously contained food at delay intervals of 24 hrs or more. In Exp 2, a juvenile gorilla was also accurate in remembering locations that had previously contained food at delays up to 10 min. The adult gorilla appeared to use a counting strategy during the search phase to minimize the number of sites visited. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Scapula form and biomechanics in gorillas

Gorillas are generating renewed interest as mounting evidence from field and molecular studies strongly suggests the western lowland (Gorilla gorilla gorilla) and eastern mountain (Gorilla gorilla beringei) gorillas are considerably more distinct than has previously been accepted. Schultz (1927, 1930, 1934) was one of the earliest investigators to document morphological differences between the two groups, noting differences in pedal, limb and scapular morphology. These differences led Schultz to conclude that while lowland gorillas retained some features suited to an arboreal habitat, the mountain gorilla had evolved into a specialized terrestrial quadruped. In particular, he noted that mountain gorillas exhibited lower values for the scapular index, higher values for ratios of infraspinous fossa vs. scapula length and spine length vs. scapula length and variability in the extent of curvature of the vertebral border. However, Schultz' observations were based upon small sample sizes of mostly adult specimens. This study extends Schultz' preliminary work by assessing, with appreciably larger sample sizes, patterns of relative growth of the scapula in these two subspecies of Gorilla. Scapula measurements were obtained for ontogenetic series of G.g. gorilla (n = 366) and G. g. beringei (n = 43). Statistical analyses reveal mountain gorillas exhibit significantly (P < 0.05) greater spine lengths and scapula breadths and smaller scapula lengths than lowland gorillas of comparable superior border lengths. However, at comparable body weights, mountain gorillas exhibit significantly shorter spines and superior borders than lowland gorillas. These differences in scapula proportions are evaluated in the context of biomechanical predictions regarding scapula form and locomotion.     

Stage 6 object concept in nonhuman primate cognition: A comparison between gorilla (Gorilla gorilla gorilla) and Japanese macaque (Macaca fuscata).

Several investigators have reported the achievement of Stage 6 object concept in a number of species of nonhuman primates. Because Stage 6 object concept implies a capacity for mental representation, such an achievement would demonstrate the presence of a crucial capacity in nonhuman primate cognition. There are, it is suggested, problems in the way nonhuman primates have been tested for Stage 6 object concept (i.e., that the tasks employed could be solved in nonrepresentational ways). The present study attempted to differentiate between representational and nonrepresentational responses in the typical task used for testing Stage 6 object concept (following the invisible displacements of an object). The performance of 2 22-mo-old Ss, a Japanese macaque and a gorilla, was compared. It was found that only the gorilla solved the task with the use of mental representation. The macaque consistently tried to solve the task by employing practical, nonrepresentational strategies. (12 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Task constraints mask great apes' ability to solve the trap-table task.

Researchers have investigated animals' causal knowledge with a task requiring subjects to use a tool to bring a reward within reach whilst avoiding a trap. Previous studies have suggested limitations in the ability of several species to avoid traps in tubes or tables. However, certain features may have inflated task difficulty. We tested 20 chimpanzees (Pan troglodytes), 7 orangutans (Pongo pygmaeus), 5 bonobos (Pan paniscus), and 5 gorillas (Gorilla gorilla) in the trap-table--a task in which subjects have to pull one of two rakes prepositioned behind two rewards on a flat surface. One of the rewards is in front of a trap into which it will fall. We investigated the effect of trap type, tool type, the number of available tools, and reinforcement regime on performance. We replicated previous findings showing that apes failed to choose the correct rake above chance. However, when they could instead choose where to insert a single tool, around 80% of the apes solved the trap-table task in the first trial, revealing an important effect of task constraints on their performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Nonenculturated Orangutans' (Pongo pygmaeus) Use of Experimenter-Given Manual and Facial Cues in an Object-Choice Task.

Several experiments have been performed, to examine whether nonhuman primates are able to make use of experimenter-given manual and facial (visual) cues to direct their attention to a baited object. Contrary to the performance of prosimians and monkeys, great apes repeatedly have shown task efficiency in experiments such as these. However, many great ape subjects used have been "enculturated" individuals. In the present study, 3 nonenculturated orangutans (Pongo pygmaeus) were tested for their ability to use experimenter-given pointing, gazing, and glancing cues in an object-choice task. All subjects readily made use of the pointing gesture. However, when subjects were left with only gazing or glancing cues, their performance deteriorated markedly, and they were not able to complete the task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Great apes select tools on the basis of their rigidity.

Wild chimpanzees select tools according to their rigidity. However, little is known about whether choices are solely based on familiarity with the materials or knowledge about tool properties. Furthermore, it is unclear whether tool manipulation is required prior to selection or whether observation alone can suffice. We investigated whether chimpanzees (Pan troglodytes) (n = 9), bonobos (Pan paniscus) (n = 4), orangutans (Pongo pygmaeus) (n = 6), and gorillas (Gorilla gorilla) (n = 2) selected new tools on the basis of their rigidity. Subjects faced an out-of-reach reward and a choice of three tools differing in color, diameter, material, and rigidity. We used 10 different 3-tool sets (1 rigid, 2 flexible). Subjects were unfamiliar with the tools and needed to select and use the rigid tool to retrieve the reward. Experiment 1 showed that subjects chose the rigid tool from the first trial with a 90% success rate. Experiments 2a and 2b addressed the role of manipulation and observation in tool selection. Subjects performed equally well in conditions in which they could manipulate the tools themselves or saw the experimenter manipulate the tools but decreased their performance if they could only visually inspect the tools. Experiment 3 showed that subjects could select flexible tools (as opposed to rigid ones) to meet new task demands. We conclude that great apes spontaneously selected unfamiliar rigid or flexible tools even after gathering minimal observational information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparative assessment of handedness for a coordinated bimanual task in chimpanzees (Pan troglodytes), gorillas (Gorilla gorilla) and orangutans (Pongo pygmaeus).

Hand preferences for a coordinated bimanual task were assessed in a sample of 31 captive gorillas (Gorilla gorilla) and 19 captive orangutans (Pongo pygmaeus) and were compared with chimpanzee (Pan Troglodytes) hand preferences in subjects that were matched on the basis of age, sex, and rearing history. The task required that the apes remove food from the inside edges of a symmetrical polyvinyl chloride pipe presented to them in their home cages. The results indicate significant species differences with chimpanzees showing population-level right-handedness and orangutans showing population-level left-handedness. The gorillas showed a nonsignificant trend toward right-handedness. The results are discussed in terms of possible ecological or biomechanical factors that may influence hand preferences in different ape species. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Infants interpret ambiguous requests for absent objects.

The current studies investigated 2 skills involved in 14- to 20- month-olds' ability to interpret ambiguous requests for absent objects: tracking others' experiences (Study 1) and representing links between speakers and object features across present and absent reference episodes (Study 2). In the basic task, 2 experimenters played separately with a different ball. The balls were placed in opaque containers. One experimenter asked infants to retrieve her ball using an ambiguous request ("Where's the ball?"). In Study 1, infants used the experimenter's prior verbal and physical contact with the ball to interpret the request. A control condition demonstrated that infants were interpreting the request and not responding to the mere presence of the experimenter. Study 2 revealed that only infants who were given stable cues to the ball's spatial location appropriately interpreted the request: When spatial information was put in conflict with a color cue, infants did not select the correct ball. Links to infants' spatial memory skills and emerging pragmatic understanding are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Imitative learning by captive western lowland gorillas (Gorilla gorilla gorilla) in a simulated food-processing task.

Although field studies have suggested the existence of cultural transmission of foraging techniques in primates, identification of transmission mechanisms has remained elusive. To test experimentally for evidence of imitation in the current study, the authors exposed gorillas (Gorilla gorilla gorilla) to an artificial fruit foraging task designed by A. Whiten and D. M. Custance (1996). Gorillas (n?=?6) watched a human model remove a series of 3 defenses around a fruit. Each of the defenses was removed using 1 of 2 alternative techniques. Subsequent video analysis of gorillas' behavior showed a significant tendency to copy the observed technique on 1 of the individual defenses and the direction of removal on another defense. This is the first statistically reliable evidence of imitation in gorillas. Sequence of defense removal was not replicated. The gorillas' responses were most similar to those of chimpanzees. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Joint-attentional states and lexical acquisition at 18 months.

Two groups of 18-mo-old infants were observed during a relatively natural play session with an adult experimenter and several toys. A novel object associated with one of the toys was labeled a dodo by the experimenter using either an attention-following strategy (i.e., introducing the label when the infant was focused on the dodo object) or an attention-switching strategy (i.e., introducing the label when the infant was focused on an alternative object). With factors such as frequency of exposure to the object label and infant compliance equivalent across the groups, infants in the attention-following procedure were more likely to correctly identify the dodo object in a subsequent comprehension task. These experimental data corroborate previous correlational observations suggesting that early lexical development is facilitated during interactions in which the caregiver is following rather than leading the infant's focus of attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The magic cup: Great apes and domestic dogs (Canis familiaris) individuate objects according to their properties.

Despite current interest in dog (Canis familiaris) cognition, very little is known about how dogs represent objects and how they compare with other species, such as the great apes. Therefore, we investigated how dogs and great apes (chimpanzees [Pan troglodytes], bonobos [Pan paniscus], orangutans [Pongo pygmaeus], gorillas [Gorilla gorilla]) individuate objects in a classical violation of expectation paradigm. We used a container (magic cup) with a double bottom that allowed us to change the type of food that subjects had seen being placed in the container. Using a 2 × 2 design, we varied whether subjects received a generally preferred food and whether the food was substituted (surprise trials) or not (baseline trials). Apes showed increased begging and looking behaviors and dogs showed increased smelling behavior. Both species stayed near the experimenter more frequently in the surprise trials compared with baseline trials. Both species reacted to positive (i.e., good food substituted for bad food) and negative (i.e., bad food substituted for good food) surprises. These results suggest that apes and dogs were able to individuate objects according to their properties or type in comparable ways. In addition, we looked for frustration and elation effects, but subjects' behaviors were not influenced by the food they saw and which they received in previous trials. (PsycINFO Database Record (c) 2011 APA, all rights reserved)