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Full-Text Articles in Organisms
Semi-Wild Chimpanzees Open Hard-Shelled Fruits Differently Across Communities, Bruce Rawlings, Marina Davilla-Ross, Sarah T. Boysen
Semi-Wild Chimpanzees Open Hard-Shelled Fruits Differently Across Communities, Bruce Rawlings, Marina Davilla-Ross, Sarah T. Boysen
Sarah Boysen, PhD
Researchers investigating the evolutionary roots of human culture have turned to comparing behaviours across nonhuman primate communities, with tool-based foraging in particular receiving much attention. This study examined whether natural extractive foraging behaviours other than tool selection differed across nonhuman primate colonies that had the same foods available. Specifically, the behaviours applied to open the hard-shelled fruits of Strychnos spp. were examined in three socially separate, semi-wild colonies of chimpanzees (Pan troglodytes) that lived under shared ecological conditions at Chimfunshi Wildlife Orphanage, and were comparable in their genetic makeup. The chimpanzees (N = 56) consistently applied six techniques to open …
Overcoming Response Bias Using Symbolic Representations Of Number By Chimpanzees (Pan Troglodytes), Sarah T. Boysen, Kimberly L. Mukobi, Gary G. Berntson
Overcoming Response Bias Using Symbolic Representations Of Number By Chimpanzees (Pan Troglodytes), Sarah T. Boysen, Kimberly L. Mukobi, Gary G. Berntson
Sarah Boysen, PhD
We previously reported that chimpanzees were unable to optimally select the smaller of two candy arrays in order to receive a larger reward. When Arabic numerals were substituted for the candy arrays, animals who had had prior training with numerical symbols showed an immediate and significant improvement in performance and were able to select reliably the smaller numeric representation in order to obtain a larger reward. Poor performance with candy arrays was interpreted as reflecting a response bias toward the intrinsic incentive and/or perceptual features of the larger array. In contrast, the Arabic numerals represent numerosity symbolically and appear to …
Spontaneous Discrimination Of Natural Stimuli By Chimpanzees (Pan Troglodytes), David A. Brown, Sarah T. Boysen
Spontaneous Discrimination Of Natural Stimuli By Chimpanzees (Pan Troglodytes), David A. Brown, Sarah T. Boysen
Sarah Boysen, PhD
Six chimpanzees (Pan troglodytes) were presented with pairs of color photographic images of 5 different categories of animals (cat, chimp, gorilla, tiger, fish). The subjects responded to each pair using symbols for "same" and "different." Both within- and between-category discriminations were tested, and all chimpanzees classified the image pairs in accordance with the 5 experimenter-defined categories under conditions of nondifferential reinforcement. Although previous studies have demonstrated identification or discrimination of natural categories by nonhuman animals, subjects were typically differentially reinforced for their responses. The present findings demonstrate that chimpanzees can classify natural objects spontaneously and that such classifications may be …
Scale-Model Comprehension By Chimpanzees (Pan Troglodytes), Valerie A. Kuhlmeier, Sarah T. Boysen, Kimberly L. Mukobi
Scale-Model Comprehension By Chimpanzees (Pan Troglodytes), Valerie A. Kuhlmeier, Sarah T. Boysen, Kimberly L. Mukobi
Sarah Boysen, PhD
The ability of chimpanzees (Pan troglodytes) to recognize the correspondence between a scale model and its real-world referent was examined. In Experiments 1 and 2, an adult female and a young adult male watched as an experimenter hid a miniature model food in 1 of 4 sites in a scale model. Then, the chimpanzees were given the opportunity to find the real food item that had been hidden in the analogous location in the real room. The female performed significantly above chance, whereas the male performed at chance level. Experiments 3 and 4 tested 5 adult and 2 adolescent chimpanzees …
The Effect Of Response Contingencies On Scale Model Task Performance By Chimpanzees (Pan Troglodytes), Valerie A. Kuhlmeier, Sarah T. Boysen
The Effect Of Response Contingencies On Scale Model Task Performance By Chimpanzees (Pan Troglodytes), Valerie A. Kuhlmeier, Sarah T. Boysen
Sarah Boysen, PhD
The effects of modified procedures on chimpanzees' (Pan troglodytes) performance in a scale model comprehension task were examined. Seven chimpanzees that previously participated in a task in which they searched an enclosure for a hidden item after watching an experimenter hide a miniature item in the analogous location in a scale model were retested under procedures incorporating response costs. In Experiment 1, chimpanzees were trained under procedures that rewarded only item retrievals occurring on the 1st search attempt. During test trials, 6 chimpanzees performed above chance, including 4 that were previously unsuccessful under the original procedures (V. A. Kuhlmeier, S. …
Primate Numerical Competence: Contributions Toward Understanding Nonhuman Cognition, Sarah T. Boysen, Karen I. Hallberg
Primate Numerical Competence: Contributions Toward Understanding Nonhuman Cognition, Sarah T. Boysen, Karen I. Hallberg
Sarah Boysen, PhD
Nonhuman primates represent the most significant extant species for comparative studies of cognition, including such complex phenomena as numerical competence, among others. Studies of numerical skills in monkeys and apes have a long, though somewhat sparse history, although questions for current empirical studies remain of great interest to several fields, including comparative, developmental, and cognitive psychology; anthropology; ethology; and philosophy, to name a few. In addition to demonstrated similarities in complex information processing, empirical studies of a variety of potential cognitive limitations or constraints have provided insights into similarities and differences across the primate order, and continue to offer theoretical …
Emotional Engagements Predict And Enhance Social Cognition In Young Chimpanzees, Kim A. Bard, Roger Bakeman, Sarah T. Boysen, David A. Leavens
Emotional Engagements Predict And Enhance Social Cognition In Young Chimpanzees, Kim A. Bard, Roger Bakeman, Sarah T. Boysen, David A. Leavens
Sarah Boysen, PhD
Social cognition in infancy is evident in coordinated triadic engagements, that is, infants attending jointly with social partners and objects. Current evolutionary theories of primate social cognition tend to highlight species differences in cognition based on human-unique cooperative motives. We consider a developmental model in which engagement experiences produce differential outcomes. We conducted a 10-year-long study in which two groups of laboratory-raised chimpanzee infants were given quantifiably different engagement experiences. Joint attention, cooperativeness, affect, and different levels of cognition were measured in 5- to 12-month-old chimpanzees, and compared to outcomes derived from a normative human database. We found that joint …
Visual Attention And Its Relation To Knowledge States In Chimpanzees, Pan Troglodytes, Megan J. Bulloch, Sarah T. Boysen, Ellen E. Furlong
Visual Attention And Its Relation To Knowledge States In Chimpanzees, Pan Troglodytes, Megan J. Bulloch, Sarah T. Boysen, Ellen E. Furlong
Sarah Boysen, PhD
Primates rely on visual attention to gather knowledge about their environment. The ability to recognize such knowledge-acquisition activity in another may demonstrate one aspect of Theory of Mind. Using a series of experiments in which chimpanzees were presented with a choice between an experimenter whose visual attention was available and another whose vision was occluded, we asked whether chimpanzees understood the relationship between visual attention and knowledge states. The animals showed sophisticated understanding of attention from the first presentation of each task. Under more complex experimental conditions, the subjects had more difficulty with species-typical processing of attentional cues and those …
Size Matters: Impact Of Item Size And Quantity On Array Choice By Chimpanzees (Pan Troglodytes), Sarah T. Boysen, Gary G. Berntson, Kimberly L. Mukobi
Size Matters: Impact Of Item Size And Quantity On Array Choice By Chimpanzees (Pan Troglodytes), Sarah T. Boysen, Gary G. Berntson, Kimberly L. Mukobi
Sarah Boysen, PhD
The authors previously reported that chimpanzees (Pan troglodytes) showed a striking bias to select the larger of 2 candy arrays, despite a reversed reward contingency in which the animals received the smaller, nonselected array as a reward, except when Arabic numerals were used as stimuli. A perceptual or incentive-based interference occurred that was overcome by symbolic stimuli. The authors of the present study examined the impact of element size in choice arrays, using 1 to 5 large and small candies. Five test-sophisticated chimpanzees selected an array from the 2 presented during each trial. Their responses were not optimal, as animals …
Language-Naive Chimpanzees (Pan Troglodytes) Judge Relations Between Relations In A Conceptual Matching-To-Sample Task, Roger K.R. Thompson, David L. Oden, Sarah T. Boysen
Language-Naive Chimpanzees (Pan Troglodytes) Judge Relations Between Relations In A Conceptual Matching-To-Sample Task, Roger K.R. Thompson, David L. Oden, Sarah T. Boysen
Sarah Boysen, PhD
Three chimpanzees with a history of conditional and numeric token training spontaneously matched relations between relations under conditions of nondifferential reinforcement. Heretofore, this conceptual ability was demonstrated only in language-trained chimpanzees. The performance levels of the language-naive animals in this study, however, were equivalent to those of a 4th animal—Sarah—whose history included language training and analogical problem solving. There was no evidence that associative factors mediated successful performance in any of the animals. Prior claims of a profound disparity between language-trained and language-naive chimpanzees apparently can be attributed to prior experience with arbitrary tokens consistently associated with abstract relations and …
Quantity-Based Interference And Symbolic Representations In Chimpanzees (Pan Troglodytes), S. T. Boysen, G. G. Berntson, M. B. Hannan, J. T. Cacioppo
Quantity-Based Interference And Symbolic Representations In Chimpanzees (Pan Troglodytes), S. T. Boysen, G. G. Berntson, M. B. Hannan, J. T. Cacioppo
Sarah Boysen, PhD
Five chimpanzees with training in counting and numerical skills selected between 2 arrays of different amounts of candy or 2 Arabic numerals. A reversed reinforcement contingency was in effect, in which the selected array was removed and the subject received the nonselected candies (or the number of candies represented by the nonselected Arabic numeral). Animals were unable to maximize reward by selecting the smaller array when candies were used as array elements. When Arabic numerals were substituted for the candy arrays, all animals showed an immediate shift to a more optimal response strategy of selecting the smaller numeral, thereby receiving …
Capuchins (Cebus Apella) Can Solve A Means-End Problem, Anna M. Yocom, Sarah T. Boysen
Capuchins (Cebus Apella) Can Solve A Means-End Problem, Anna M. Yocom, Sarah T. Boysen
Sarah Boysen, PhD
Three capuchin monkeys (Cebus apella) were tested on a 2-choice discrimination task designed to examine their knowledge of support, modeled after Hauser, Kralik, and Botto-Mahan’s (1999) experiments with tamarins. This task involved a choice between 2 pieces of cloth, including 1 with a food reward placed on its surface, and a second cloth with the food reward next to its surface. After reliably solving the basic problem, the capuchins were tested with various alternations of the original food reward and cloth. The capuchins were able to solve the initial task quickly, and generalize their knowledge to additional functional and nonfunctional …
Chimpanzees (Pan Troglodytes) Recognize Spatial And Object Correspondences Between A Scale Model And Its Referent, Valerie A. Kuhlmeier, Sarah T. Boysen
Chimpanzees (Pan Troglodytes) Recognize Spatial And Object Correspondences Between A Scale Model And Its Referent, Valerie A. Kuhlmeier, Sarah T. Boysen
Sarah Boysen, PhD
In the present study, the contributions of spatial and object features to chimpanzees’ comprehension of scale models were examined. Seven chimpanzees that previously demonstrated the ability to use a scale model as an information source for the location of a hidden item were tested under conditions manipulating the feature correspondence and spatial-relational correspondence between objects in the model and an outdoor enclosure. In Experiment 1, subjects solved the task under two conditions in which one object cue (color or shape) was unavailable, but positional cues remained. Additionally, performance was above chance under a third condition in which both types of …
Constructive And Deconstructive Tool Modification By Chimpanzees (Pan Troglodytes), Amanda E. Bania, Stephany Harris, Hannah R. Kinsley, Sarah T. Boysen
Constructive And Deconstructive Tool Modification By Chimpanzees (Pan Troglodytes), Amanda E. Bania, Stephany Harris, Hannah R. Kinsley, Sarah T. Boysen
Sarah Boysen, PhD
Nine chimpanzees (Pan troglodytes) were tested for their ability to assemble or disassemble the appropriate tool to obtain a food reward from two different apparatus. In its deconstructed form, the tool functioned as a probe for one apparatus. In its constructed form, the tool functioned as a hook, appropriate for a second apparatus. Each subject completed four test trials with each apparatus type. Tool types were randomized and counter-balanced between the two forms. Results demonstrated that adult and juvenile chimpanzees (N = 7) were successful with both tool types, while two infant chimpanzees performed near chance. Off-line video analyses revealed …
Comprehension Of Functional Support By Enculturated Chimpanzees Pan Troglodytes, Anna M. Yocom, Sarah T. Boysen
Comprehension Of Functional Support By Enculturated Chimpanzees Pan Troglodytes, Anna M. Yocom, Sarah T. Boysen
Sarah Boysen, PhD
Studies of causal understanding of tool relationships in captive chimpanzees have yielded disparate findings, particularly those reported by Povinelli & colleagues (2000) for tool tasks by laboratory chimpanzees. The present set of experiments tested nine enculturated chimpanzees on three versions of a support task, as described by Povinelli (2000), during which food rewards were presented in different experimental configurations. In Experiment 1, stimulus pairs included a choice between a cloth with a reward on the upper right corner or with a second reward off the cloth, adjacent to a corner, with the second pair comprised of a cloth with food …