Finding hidden food: Behavior on visible displacement tasks by mynahs (Gracula religiosa) and pigeons (Columba livia).

Four visible displacement tasks showed that pigeons can learn to find hidden food but revealed little evidence of spontaneous retrieval. In Experiment 1, given a choice between 2 screens, 1 of which concealed food, pigeons performed at chance level. In Experiment 2, when shown a moving cart of grain that disappeared into a tunnel and reemerged, they spontaneously followed the cart if the tunnel was clear but not if it was opaque. After learning to follow the cart, they would follow it when it was filled with grit. In Experiment 3, pigeons were rewarded for pecking at a key when a horizontally moving figure disappeared behind an occluder. Performance was characterized by a time-waiting rule. Experiment 4 describes a species comparison in finding food hidden in 1 of 4 compartments: As predicted from ecological considerations, mynahs performed better than pigeons. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Numerical judgments by chimpanzees (Pan troglodytes) in a token economy.

We presented four chimpanzees with a series of tasks that involved comparing two token sets or comparing a token set to a quantity of food. Selected tokens could be exchanged for food items on a one-to-one basis. Chimpanzees successfully selected the larger numerical set for comparisons of 1 to 5 items when both sets were visible and when sets were presented through one-by-one addition of tokens into two opaque containers. Two of four chimpanzees used the number of tokens and food items to guide responding in all conditions, rather than relying on token color, size, total amount, or duration of set presentation. These results demonstrate that judgments of simultaneous and sequential sets of stimuli are made by some chimpanzees on the basis of the numerousness of sets rather than other non-numerical dimensions. The tokens were treated as equivalent to food items on the basis of their numerousness, and the chimpanzees maximized reward by choosing the larger number of items in all situations. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Chimpanzees (Pan troglodytes) Respond to Nonvisible Sets After One-by-One Addition and Removal of Items.

Two chimpanzees (Pan troglodytes) made numerousness judgments of nonvisible sets of items. In Experiment 1, 1-10 items were dropped 1 at a time into an opaque cup, and then an additional 1-10 items were dropped 1 at a time into another opaque cup. The chimpanzees' performance levels were high and were more dependent on factors indicative of an analogue-magnitude mechanism for representation of set size than on an object file mechanism. In Experiment 2, a 3rd visible set was made available after the sequential presentation of the first 2 sets. The chimpanzees again performed at high levels in selecting the largest of the 3 sets. In Experiment 3, 1 of the 2 initially presented sets was reduced in number by the sequential removal of 1, 2, or 3 items. Both chimpanzees performed above chance levels for the removal of 1, but not more than 1, item. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Locomotor expertise predicts infants’ perseverative errors.

This research examined the development of inhibition in a locomotor context. In a within-subjects design, infants received high- and low-demand locomotor A-not-B tasks. In Experiment 1, walking 13-month-old infants followed an indirect path to a goal. In a control condition, infants took a direct route. In Experiment 2, crawling and walking 13-month-old infants crawled through a tunnel to reach a goal at the other end and received the same control condition as in Experiment 1. In both experiments, perseverative errors occurred more often in the high-demand condition than in the low-demand condition. Moreover, in Experiment 2, walkers perseverated more than crawlers, and extent of perseveration was related to infants’ locomotor experience. In Experiment 3, the authors addressed a possible confound in Experiment 2 between locomotor expertise and locomotor posture. Novice crawlers perseverated in the difficult tunnels condition, behaving more like novice walkers than expert crawlers. As predicted by a cognitive capacity account of infant perseveration, overtaxed attentional resources resulted in a cognition–action trade-off. Experts who found the task less motorically effortful than novices had more cognitive resources available for problem solving. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Grip morphology and hand use in chimpanzees (Pan troglodytes): Evidence of a left hemisphere specialization in motor skill.

Three experiments on grip morphology and hand use were conducted in a sample of chimpanzees. In Experiment 1, grip morphology when grasping food items was recorded, and it was found that subjects who adopted a precision grip were more right-handed than chimpanzees using other grips. In Experiment 2, the effect of food type on grasping was assessed. Smaller food items elicited significantly more precision grips for the right hand. In Experiment 3, error rates in grasping foods were compared between the left and right hands. Significantly more errors were made for the left compared with the right hand. The cumulative results indicate that chimpanzees show a left-hemisphere asymmetry in motor skill that is associated with the use of precision grips. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrete quantity judgments in the great apes (Pan paniscus, Pan troglodytes, Gorilla gorilla, Pongo pygmaeus): The effect of presenting whole sets versus item-by-item.

The authors examined quantity-based judgments for up to 10 items for simultaneous and sequential whole sets as well as for sequentially dropped items in chimpanzees (Pan troglodytes), gorillas (Gorilla gorilla), bonobos (Pan paniscus), and orangutans (Pongo pygmaeus). In Experiment 1, subjects had to choose the larger of 2 quantities presented in 2 separate dishes either simultaneously or 1 dish after the other. Representatives of all species were capable of selecting the larger of 2 quantities in both conditions, even when the quantities were large and the numerical distance between them was small. In Experiment 2, subjects had to select between the same food quantities sequentially dropped into 2 opaque cups so that none of the quantities were ever viewed as a whole. The authors found some evidence (albeit weaker) that subjects were able to select the larger quantity of items. Furthermore, the authors found no performance breakdown with the inclusion of certain quantities. Instead, the ratio between quantities was the best performance predictor. The authors conclude that quantity-based judgments rely on an analogical system, not a discrete object file model or perceptual estimation mechanism, such as subitizing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Referential Communication by Chimpanzees (Pan troglodytes).

Two experiments were conducted to assess the referential function of chimpanzee (Pan troglodytes) gestures to obtain food. The chimpanzees received 1 trial per condition. In Experiment 1 (N = 101), in full view of the chimpanzee, a banana was placed on top of 1 of 2 inverted buckets or was hidden underneath 1 of the buckets. In Experiment 2 (N = 35), 4 conditions were presented in constant order: (a) no food, no observer; (b) no food, observer present; (c) food present, no observer; and (d) food present, observer present. Gestures and visual orienting were used socially and referentially. The capacity for nonverbal reference may predate the Hominidae-Pongidae split, and the development of nonverbal reference may be independent of human species-specific adaptations for speech. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Do chimpanzees (Pan troglodytes) spontaneously take turns in a reciprocal cooperation task?

Reciprocity is considered to be an explanation for altruism toward nonkin. Although there have been many theoretical studies and reciprocity is arguably prevalent in humans, little experimental work has investigated the proximate mechanism of reciprocity in nonhuman animals. The authors tested whether pairs of chimpanzees (Pan troglodytes) would achieve reciprocal cooperation, that is, whether chimpanzees take turns playing donor and recipient roles in an other-rewarding token insertion task. In this task, when a chimpanzee inserts a token into a vending machine, a food reward is delivered to another chimpanzee in an adjacent booth. For 3 pairs of chimpanzees, token insertion persisted in an alternate condition, in which the participants necessarily had to insert tokens alternately, but not in a free condition, in which they freely took turns inserting tokens. In the free condition, one of the chimpanzees was observed to perform a possible solicitation toward the partner who had previously inserted fewer tokens. These findings suggest that there is some difficulty in the occurrence of reciprocal cooperation in chimpanzees. Chimpanzees, differently from humans, might play a donor’s role only on the partner’s request, but not spontaneously. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Information integration about object–object relationships by chimpanzees (Pan troglodytes).

Three experiments tested the ability to integrate information about object–object relationships in 2 chimpanzees. In Experiment 1, the subjects were trained to match 1 part of a 2-part object to its other part, match a tool to its assembled object, match a container to its tool, and match a tool to its container. In Experiment 2, the subjects were trained to match a picture of the sample. One subject learned this type of matching task and was then tested on whether she could choose the pictures of related items in Experiment 1. Although the subject was reinforced irrespective of her choices, she chose pictures of items related to the sample when there was no picture of the sample. Experiment 3 showed that the subject was able to match a picture of the item among related items. The results suggest that the subject might integrate information about relationships acquired in Experiment 1 and organize it to make networks of related items. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial Memory and Monitoring of Hidden Items Through Spatial Displacements by Chimpanzees (Pan troglodytes).

This study examined chimpanzee (Pan troglodytes) short-term memory for food location in near space. In Experiments 1 and 2, either 1 or 2 items (chocolate pieces) were hidden in an array of 3 or 5 containers that either remained stationary or were rotated 180° or 360°. When the array remained stationary, the chimpanzees remembered both item locations. When arrays were rotated, however, chimpanzees found only 1 item. In Experiment 3, 2 items were hidden in an array of 7 cups. Both items were found at levels significantly better than chance. Ninety percent of errors were made after the 1st item was found, and errors reflected memory failure rather than a failure of inhibitory control. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Self-experience as a mechanism for learning about others: A training study in social cognition.

Using a gaze-following task, the authors assessed whether self-experience with the view-obstructing properties of blindfolds influenced infants' understanding of this effect in others. In Experiment 1, 12-month-olds provided with blindfold self-experience behaved as though they understood that a person wearing a blindfold cannot see. When a blindfolded adult turned to face an object, these infants gaze followed significantly less than control infants who had either (a) seen and felt the blindfold but whose view had not been obstructed by it or (b) experienced a windowed blindfold through which they could see. In Experiment 2, 18-month-olds experienced either (a) a trick blindfold that looked opaque but could be seen through, (b) an opaque blindfold, or (c) baseline familiarization. Infants receiving trick-blindfold experience now followed a blindfolded adult's gaze significantly more than controls. The authors propose 3 mechanisms underlying infants' capacity to use self-experience as a framework for understanding the visual perception of others. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual discrimination by heifers (Bos taurus) of their own species.

Species discrimination has been described in several taxa but rarely in domestic animals. In contrast to wild species, domestic species present a great phenotypic variety. This study investigated whether 10 Prim'Holstein heifers (Bos taurus) could discriminate images of cows from images of other domestic animals. The experiment was based on simultaneous discrimination. Responses were obtained through instrumental conditioning using a food reward. In Experiment 1, the reward was associated with a cow face and, in the reversal learning task, with faces of other domestic species. The results showed that in both tasks, cows were able to reach the criterion in few sessions. Therefore, despite great phenotypic variety (a cognitive challenge) cows were able to visually discriminate their own species from other domestic species. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Summation and numerousness judgments of sequentially presented sets of items by chimpanzees (Pan troglodytes).

Summation and numerousness judgments by 2 chimpanzees (Pan troglodytes) were investigated when 2 quantities of M&Ms were presented sequentially, and the quantities were never viewed in their totality. Each M&M was visible only before placement in 1 of 2 cups. In Experiment 1, sets of 1 to 9 M&Ms were presented. In Experiment 2, the quantities in each cup were presented as 2 smaller sets (e.g., ?+?2 vs. 4?+?1). In Experiment 3, the quantities were presented as 3 smaller sets (e.g., 2?+?2?+?3 vs. 3?+?4?+?1). In Experiment 4, an M&M was removed from 1 set before the chimpanzees' selection. In Experiments 1 and 2, the chimpanzees selected the larger quantity on significantly more trials than would be predicted by chance. In Experiments 3 and 4, 1 chimpanzee performed at a level significantly better than chance. Therefore, chimpanzees mentally represent quantity and successfully combine and compare nonvisible, sequentially presented sets of items. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A Comparative Study of the Use of Visual Communicative Signals in Interactions Between Dogs (Canis familiaris) and Humans and Cats (Felis catus) and Humans.

Dogs' (Canis familiaris) and cats' (Felis catus) interspecific communicative behavior toward humans was investigated. In Experiment 1, the ability of dogs and cats to use human pointing gestures in an object-choice task was compared using 4 types of pointing cues differing in distance between the signaled object and the end of the fingertip and in visibility duration of the given signal. Using these gestures, both dogs and cats were able to find the hidden food; there was no significant difference in their performance. In Experiment 2, the hidden food was made inaccessible to the subjects to determine whether they could indicate the place of the hidden food to a naive owner. Cats lacked some components of attention-getting behavior compared with dogs. The results suggest that individual familiarization with pointing gestures ensures high-level performance in the presence of such gestures; however, species-specific differences could cause differences in signaling toward the human. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The relationship between problem solving and inhibitory control: Cotton-top tamarins ( Saguinus oedipus ) performance on a reversed contingency task.

To explore the relationship between problem solving and inhibitory control, the authors present 4 experiments on cotton-top tamarins (Saguinus oedipus) using a reverse-reward contingency task. In Experiment 1, 1 group of tamarins was given a choice between a small and a large quantity of food. Whichever quantity the tamarins reached for first, they received the alternative. The tamarins consistently picked the larger quantity, thereby receiving the smaller. A 2nd group of tamarins was given the same task, except that if they reached for the larger quantity of food, they received nothing. The tamarins continued to pick the larger quantity, even though this resulted in no food. In addition, most of the tamarins continued to pick the larger quantity even when the food payoff for choosing the smaller quantity was increased (Experiment 2) or when the visual salience of the food was reduced (Experiment 3). Experiment 4 was based on the finding that chimpanzees (Pan troglodytes) that have been trained on the concept of number can solve the reversed contingency task if the food is replaced by Arabic numerals. With the help of a color association, and a higher cost incurred by picking the color associated with 3 food items, the tamarins learned to pick the color associated with... (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cooperatively breeding cottontop tamarins (Saguinus oedipus) do not donate rewards to their long-term mates.

This study tested the hypothesis that cooperative breeding facilitates the emergence of prosocial behavior by presenting cottontop tamarins (Saguinus oedipus) with the option to provide food rewards to pair-bonded mates. In Experiment 1, tamarins could provide rewards to mates at no additional cost while obtaining rewards for themselves. Contrary to the hypothesis, tamarins did not demonstrate a preference to donate rewards, behaving similar to chimpanzees in previous studies. In Experiment 2, the authors eliminated rewards for the donor for a stricter test of prosocial behavior, while reducing separation distress and food preoccupation. Again, the authors found no evidence for a donation preference. Furthermore, tamarins were significantly less likely to deliver rewards to mates when the mate displayed interest in the reward. The results of this study contrast with those recently reported for cooperatively breeding common marmosets, and indicate that prosocial preferences in a food donation task do not emerge in all cooperative breeders. In previous studies, cottontop tamarins have cooperated and reciprocated to obtain food rewards; the current findings sharpen understanding of the boundaries of cottontop tamarins’ food-provisioning behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory of movies by chimpanzees (Pan troglodytes).

How do animals remember what they see in daily life? The processes involved in remembering such visual information may be similar to those used in interpreting moving images on a monitor. In Experiment 1, 4 adult chimpanzees (Pan troglodytes) were required to discriminate between movies using a movie-to-movie matching-to-sample task. All chimpanzees demonstrated the ability to discriminate movies from the very 1st session onward. In Experiment 2, the ability to retain a movie was investigated through a matching-to-sample task using movie stills. To test which characteristics of movies are relevant to memory, the authors compared 2 conditions. In the continuous condition, the scenes comprising the movie progressed gradually, whereas in the discrete condition, the authors introduced a sudden change from one scene to another. Chimpanzees showed a recency effect only in the discrete condition, suggesting that composition and temporal order of scenes were used to remember the movies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Relative Numerousness Judgment and Summation in Young and Old Western Lowland Gorillas.

The relationship between age, relative numerousness judgment, and summation was investigated in 11 Western lowland gorillas (Gorilla gorilla gorilla). Experiments 1 and 2 evaluated the gorillas' ability to select the larger of 2 food quantities before and with training. The majority of gorillas did not reliably select the larger quantity in Experiment 1 until receiving training to do so in Experiment 2. Experiment 3 evaluated their ability to select the larger of 2 pairs of quantities. All gorillas selected the larger pair more often than chance, and the old were less accurate and slower than were the young. For most gorillas, performance in relative numerousness judgment with training and summation was comparable with previous reports in chimpanzees and orangutans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of response contingencies on scale model task performance by chimpanzees (Pan troglodytes).

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. T. Boysen, & K. L. Mukobi, 1999). Experiment 2 compared performance under the new and original procedures. Results indicated that for some chimpanzees, performance depended on procedures that decreased the use of competing search strategies and encouraged strategies based on information from the scale model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of self-recognition in chimpanzees (Pan troglodytes).

Chimpanzees demonstrate the ability to recognize themselves in mirrors, yet investigations of the development of self-recognition in chimpanzees are sparse. 12 young chimpanzees, grouped by age, were given mirror exposure and tested for self-recognition and contingent movement. All 6 juveniles, 4 and 5 yrs old, exhibited mirror-guided, mark-directed behavior and clear evidence of self-recognition. In contrast, among the infants, only the oldest group of 2.5-yr-olds exhibited clear evidence of self-recognition. All chimpanzees exhibited both self-directed behaviors and contingent movements. These results suggest that self-recognition occurs at a slightly older age in chimpanzees than in human infants. In humans, self-recognition is linked with other cognitive abilities. The results conform to the general pattern that great apes exhibit many cognitive skills comparable to those of 2-yr-old humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)