Jerald D. Kralik

Problem solving and functional design features : experiments on cotton-top tamarins, Saguinus oedipus oedipus

In any problem-solving situation, there are features associated with the problem that are relevant from a functional perspective and other features that are irrelevant. To determine whether animals are sensitive to the distinction between functionally relevant and irrelvant features of a problem, we conducted two main experiments with a New World monkey, the cotton-top tamarin. In the first condition of both experiments, subjects were required to pull a piece of cloth to gain access to a piece of food. The first experiment involved choosing between food that was on the cloth and food that was off the cloth. The second experiment involved choosing between food that was on a connected piece of cloth and food that was on two pieces of cloth separated by a horizontal gap. Having learned to solve either of these two problems, we conducted a series of probe conditions to determine whether the tamarins would generalize to changes in the shape, size, colour, and texture of the cloth and food, the position of the food relative to the cloth, and the type of connection between two pieces of cloth. For most of the probe conditions, the tamarins readily generalized, showing no decrement in performance, even on the first trial. For other conditions, involving apparently more subtle discrimination (e.g. a narrow vertical gap between the two pieces of cloth), explicit training was required. These results indicate that tamarins solve means-end relationships, and that their ability depends on a discrimination between properties that are functionally relevant as opposed to irrelevant. Copyright 1999 The Association for the Study of Animal Behaviour.

The relationship between problem solving and inhibitory control: cotton-top tamarin (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 1 food item. These results are compared with those obtained from studies of other primate species, highlighting the importance of comparative studies of problem solving that use comparable methods.

Learning to inhibit prepotent responses: successful performance by rhesus macaques, Macaca mulatta, on the reversed-contingency task

To reinvestigate whether macaque monkeys could learn the reversed-contingency task, we trained six rhesus monkeys on the problem. On each trial, the monkeys chose between one and four pieces of the same food item. If a monkey selected four pieces of food, it received one instead; choice of one piece of food led to the receipt of four. All of the monkeys initially tended to select the larger quantity of food, but eventually learned to choose the smaller amount. The results confirmed a previous report that macaque monkeys quickly reached a performance level of roughly 50% ‘correct’, defined as choosing the smaller amount of food, and some individuals continued to perform at that level for a protracted period of testing. Contrary to that report, however, the present findings show that macaque monkeys can master the reversed-contingency task.

Inhibitory Control and Response Selection in Problem Solving: How Cotton-Top Tamarins (Saguinus oedipus) Overcome a Bias for Selecting the Larger Quantity of Food.

When presented with a choice between 1 and 3 pieces of food in a type of reversed contingency task, 4 cotton-top tamarins (Saguinus oedipus) consistently chose the 3 pieces of food and received nothing, even though the choice of 1 piece would have yielded 3. However, in a task in which the tamarins received the 1 piece of food when they chose it, all subjects learned to select 1 over 3. Thus, the tamarins prior failure on the reversed contingency task did not result entirely from an inherent inability to suppress the prepotent response of reaching to the larger of 2 quantities of food. After the experience of selecting the smaller quantity and receiving it, all of the tamarins solved the version of the reversed contingency task that they failed initially. These results suggest that the tamarins initial failure may have reflected a difficulty with selecting an alternative response option.

Multitasking of Attention and Memory Functions in the Primate Prefrontal Cortex

In motor and sensory areas of cortex, neuronal activity often depends on the location of a movement target or a sensory stimulus, with each neuron tuned to a single part of space called a preferred direction (when motor) or a receptive field (when sensory). As we previously reported, some neurons in the monkey prefrontal cortex are tuned to two parts of space, which we interpreted as reflecting attention and working memory, respectively. Monkeys performed a behavioral task in which they attended to a visual stimulus at one location while remembering a second place, and these locations were varied from trial to trial to assess spatial tuning. Most spatially tuned neurons specialized in either attentional or mnemonic processing, but about one-third of the cells showed tuning for both. Here, we show that the latter population, called multitasking neurons, improves the encoding of both the attended and remembered locations. These neurons do so for three reasons: (1) the preferred directions for attention and for working memory usually differ (and often diametrically oppose one another), (2) they have stronger tuning than specialized cells, and (3) pairs of multitasking neurons represent these cognitive parameters more efficiently than pairs that include even a single specialized cell. These findings suggest that multitasking neurons provide a computational advantage for behaviors that place simultaneous demands on two or more cognitive processes.

Face processing in cotton-top tamarins (Saguinus oedipus)

Abstract. Current research on face processing in primates has focused on a few species, mostly macaques and chimpanzees; to date, only one New World monkey, the squirrel monkey, has been tested. We explored face processing, and the inversion effect in particular, in a New World primate species, the cotton-top tamarin (Saguinus oedipus). In phasexa01 of our study, we trained subjects to discriminate between two faces and two scrambled faces; we then presented the tamarins with a series of novel probes in order to determine the features underlying classification. Results showed that the tamarins relied on the external contour of the face for discrimination more than the internal features and their configuration. Statistical analyses revealed no differences in accuracy or response times to upright versus inverted stimuli, and thus no inversion effect. In phasexa02, we provided subjects with additional training on the face versus scrambled face discrimination task in order to focus their attention on the configuration of the internal features. Accuracy data revealed individual differences in how tamarins classified these stimuli, even though each subject was trained in the same way. In phasexa03, we tested for generalization to a new set of face stimuli, as well as for the capacity to show an inversion effect. For one subject who attended to the configuration of internal features, we found significant evidence of generalization, but no evidence for an inversion effect.

A nonhuman primate's perception of object relations: experiments on cottontop tamarins, Saguinus oedipus

Abstract Objects in nature often have spatial and functional relationships with other objects. For example, fruit may be connected to tree branches, bushes sometimes function as landmarks for home, and stones are functionally associated with nuts when they are used to crack the nuts open. Although animals may use the spatial and functional relationships between specific objects, it is important for ethologists interested in cognitive mechanisms to ask whether animals understand the spatial relationship between objects in a more general and abstract way. In this experiment, we ask whether a small New World monkey, the cottontop tamarin, is capable of perceiving the abstract relational concept of ‘connectedness’. Using a traditional operant paradigm, subjects were required to press one button to images with connected objects, and another button to images with separated objects. In Phase 1 of the experiment, subjects received training with only one connected and one separated image. Following training, probe images were presented in which features such as colour, texture and shape were systematically manipulated to determine which features were more important in stimulus classification. Accuracies and reaction times of responses were recorded. On the basis of their performance, the tamarins appeared to recognize that changes in the colour or texture of two objects plays no functional role in determining whether such objects are connected or separated. In contrast, changes in the shape and distance between two objects does play an important functional role, and the tamarins appeared to be sensitive to such changes. In Phase 2, subjects received training with a larger set of images. After this training, classification accuracy remained significantly above chance with most probes, suggesting that the tamarins had acquired a more general connectedness concept. In Phase 3, novel images were presented. Classification accuracy was significantly above chance for many of the novel images. Overall, results suggest that tamarins perceive spatial relationships between stimuli to some extent and can classify images based in part on their spatial relationship. Other recent experiments have shown that cottontop tamarins respond to spatial relationships even better than in the current experiment when they have to act directly on the objects. The difference between these results suggests that tamarins perceive the spatial relationships between objects more readily in the context of an ecologically valid problem.

Life beyond the mirror: a reply to Anderson & Gallup

No abstractCopyright 1997 The Association for the Study of Animal BehaviourCopyright 1997The Association for the Study of Animal Behaviour.