PubMed Health⌕ Search

Biomedical subjects

Laurie R Santos

Publications and source records attributed to Laurie R Santos.

15 recordsLinked to original sources
PubMed2006

Reflections of other minds: how primate social cognition can inform the function of mirror neurons.

Mirror neurons, located in the premotor cortex of macaque monkeys, are activated both by the performance and the passive observation of particular goal-directed actions. Although this property would seem to make them the ideal neural substrate for imitation, the puzzling fact is that monkeys simply do not imitate. Indeed, imitation appears to be a uniquely human ability. We are thus left with a fascinating question: if not imitation, what are mirror neurons for? Recent advances in the study of non-human primate social cognition suggest a surprising potential answer.

Animals↗
PubMed2006

Evidence for kind representations in the absence of language: experiments with rhesus monkeys (Macaca mulatta).

How do we come to recognize and represent different kinds of objects in the world? Some developmental psychologists have hypothesized that learning language plays a crucial role in this capacity. If this hypothesis were correct, then non-linguistic animals should lack the capacity to represent objects as kinds. Previous research with rhesus monkeys (Macaca mulatta) has shown that this species can successfully individuate different kinds of objects - monkeys who saw one kind of object hidden inside a box searched longer after finding a different kind of object. However, in these studies and the infant studies on which they were based, the objects to be individuated differed both in kind and in properties. Thus, subjects in these experiments may not be representing the kinds of objects per se, but instead only their immediate perceptual properties. Here, we show that rhesus monkeys successfully individuate different kinds of objects even when their perceptual properties are held constant. Although these data provide the best evidence to date that language is not necessary to represent kinds, we discuss our findings in terms of possible associative hypotheses as well.

Analysis of Variance↗
PubMed2006

How capuchin monkeys (Cebus apella) quantify objects and substances.

Humans and nonhuman animals appear to share a capacity for nonverbal quantity representations. But what are the limits of these abilities? Results of previous research with human infants suggest that the ontological status of an entity as an object or a substance affects infants' ability to quantify it. We ask whether the same is true for another primate species-the New World monkey Cebus apella. We tested capuchin monkeys' ability to select the greater of two quantities of either discrete objects or a nonsolid substance. Participants performed above chance with both objects (Experiment 1) and substances (Experiment 2); in both cases, the observed performance was ratio dependent. This finding suggests that capuchins quantify objects and substances similarly and do so via analog magnitude representations.

Animals↗
PubMed2006

Units of visual individuation in rhesus macaques: objects or unbound features?

Vision begins with the processing of unbound visual features, which must eventually be bound together into object representations. Such feature binding is required for coherent visual perception, and accordingly has received a considerable amount of study in several domains. Neurophysiological work, often in monkeys, has revealed the details of how and where feature binding occurs in the brain, but methodological limitations have not allowed this research to elucidate just how feature binding operates spontaneously in real-world situations. In contrast, behavioral work with human infants has demonstrated how we use simpler unbound features to individuate and identify objects over time and occlusion in many types of events, but this work has not typically been able to isolate the role of feature binding in such processing. Here we provide a method for assessing the spontaneity and fidelity of feature binding in non-human primates, as this process is utilized in real-world situations, including simple foraging behaviors. Using both looking-time and manual-search measures in a natural environment, we show that free-ranging rhesus macaques (Macaca mulatta) spontaneously bind features in order to individuate objects across time and occlusion in dynamic events. This pattern of results demonstrates that feature binding is used in subtle ways to guide ecologically relevant behavior in a non-human animal, spontaneously and reliably, in its natural environment.

Animals↗
PubMed2005

Probing the limits of tool competence: experiments with two non-tool-using species (Cercopithecus aethiops and Saguinus oedipus).

Non-human animals vary in their ability to make and use tools. The goal of the present study was to further explore what, if anything, differs between tool-users and non-tool-users, and whether these differences lie in the conceptual or motor domain. We tested two species that typically do not use tools-cotton top tamarins (Saguinus oedipus) and vervet monkeys (Cercopithecus aethiops)-on problems that mirrored those designed for prolific tool users such as chimpanzees. We trained subjects on a task in which they could choose one of two canes to obtain an out-of-reach food reward. After training, subjects received several variations on the original task, each designed to examine a specific conceptual aspect of the pulling problem previously studied in other tool-using species. Both species recognized that effective pulling tools must be made of rigid materials. Subsequent conditions revealed significant species differences, with vervets outperforming tamarins across many conditions. Vervets, but not tamarins, had some recognition of the relationship between a tool's orientation and the position of the food reward, the relationship between a tool's trajectory and the substance that it moves on, and that tools must be connected in order to work properly. These results provide further evidence that tool-use may derive from domain-general, rather than domain-specific cognitive capacities that evolved for tool use per se.

Animals↗
PubMed2005

Primate cognition: putting two and two together.

The human mind has the capacity for abstract numerical representations that cut across different sensory modalities. New research with monkeys shows that this mathematical achievement is not unique to our species.

Acoustic Stimulation↗
PubMed2005

Rhesus monkeys attribute perceptions to others.

Paramount among human cognitive abilities is the capacity to reason about what others think, want, and see--a capacity referred to as a theory of mind (ToM). Despite its importance in human cognition, the extent to which other primates share human ToM capacities has for decades remained a mystery. To date, primates [1, 2] have performed poorly in behavioral tasks that require ToM abilities, despite the fact that some macaques are known to encode social stimuli at the level of single neurons [3-5]. Here, we presented rhesus macaques with a more ecologically relevant ToM task in which subjects could "steal" a contested grape from one of two human competitors. In six experiments, monkeys selectively retrieved the grape from an experimenter who was incapable of seeing the grape rather than an experimenter who was visually aware. These results suggest that rhesus macaques possess an essential component of ToM: the ability to deduce what others perceive on the basis of where they are looking. These results converge with new findings illustrating the importance of competitive paradigms in apes [6]. Moreover, they raise the possibility that, in primates, cortical cells thought to encode where others are looking [7] may encode what those individuals see as well.

Animals↗
PubMed2005

Expectations about numerical events in four lemur species (Eulemur fulvus, Eulemur mongoz, Lemur catta and Varecia rubra).

Although much is known about how some primates--in particular, monkeys and apes--represent and enumerate different numbers of objects, very little is known about the numerical abilities of prosimian primates. Here, we explore how four lemur species (Eulemur fulvus, E. mongoz, Lemur catta, and Varecia rubra) represent small numbers of objects. Specifically, we presented lemurs with three expectancy violation looking time experiments aimed at exploring their expectations about a simple 1+1 addition event. In these experiments, we presented subjects with displays in which two lemons were sequentially added behind an occluder and then measured subjects' duration of looking to expected and unexpected outcomes. In experiment 1, subjects looked reliably longer at an unexpected outcome of only one object than at an expected outcome of two objects. Similarly, subjects in experiment 2 looked reliably longer at an unexpected outcome of three objects than at an expected outcome of two objects. In experiment 3, subjects looked reliably longer at an unexpected outcome of one object twice the size of the original than at an expected outcome of two objects of the original size. These results suggest that some prosimian primates understand the outcome of simple arithmetic operations. These results are discussed in light of similar findings in human infants and other adult primates.

Animals↗
PubMed2005

Means-means-end tool choice in cotton-top tamarins (Saguinus oedipus): finding the limits on primates' knowledge of tools.

Most studies of animal tool use require subjects to use one object to gain access to a food reward. In many real world situations, however, animals perform more than one action in sequence to achieve their goals. Of theoretical interest is whether animals have the cognitive capacity to recognize the relationship between consecutive action sequences in which there may be one overall goal and several subgoals. Here we ask if cotton-top tamarins, a species that in captivity uses tools to solve means-end problems, can go one step further and use a sequence of tools (means) to obtain food (end). We first trained subjects to use a pulling tool to obtain a food reward. After this initial training, subjects were presented with problems in which one tool had to be used in combination with a second in order to obtain food. Subjects showed great difficulty when two tools were required to obtain the food reward. Although subjects attended to the connection between the tool and food reward, they ignored the physical connection between the two tools. After training on a two-tool problem, we presented subjects with a series of transfer tests to explore if they would generalize to new types of connections between the tools. Subjects readily transferred to new connections. Our results therefore provide the first evidence to date that tamarins can learn to solve problems involving two tools, but that they do so only with sufficient training.

Animals↗
PubMed2005

How prosimian primates represent tools: experiments with two lemur species (Eulemur fulvus and Lemur catta).

The authors examined how 2 lemur species (Eulemur fulvus and Lemur catta) reason about tools. Experiment 1 allowed subjects to use 1 of 2 canes to retrieve an inaccessible food reward. Lemurs learned to solve this problem as quickly as other primates. Experiment 2 then presented subjects with novel tools differing from the originals along one featural dimension. Subjects attended more to tools' sizes than to their colors and made no distinction between tools' shapes and textures. Experiments 3 and 4 presented problems in which some of the tools' orientations had to be modified relative to the food. Subjects performed well on these problems, sometimes modifying the position of the tool. These results are discussed in light of the performance of other primates on this task.

Animals↗
PubMed2004

Dynamic object individuation in rhesus macaques: a study of the tunnel effect.

A manual-search experiment with rhesus monkeys (Macaca mulatta) explored dynamic object individuation in the tunnel effect: Subjects watched as a lemon rolled down a ramp and came to rest behind a tunnel (Occluder 1) and then as a kiwifruit emerged and became occluded at the end of its path behind a screen (Occluder 2). When the kiwifruit emerged at about the time that the lemon should have (had it continued its motion), subjects searched for food only behind Occluder 2-apparently perceiving the lemon to have transformed into a kiwifruit on the basis of spatiotemporally continuous motion. In contrast, when a brief pause interrupted the occlusion of the lemon and the emergence of the kiwifruit, monkeys searched for food behind both occluders. With further control conditions, this experiment demonstrates a spatiotemporal bias-similar to a bias found in adult visual perception-in the computation of object persistence in the context of a dynamic correspondence problem.

Animals↗
PubMed2004

'Core knowledges': a dissociation between spatiotemporal knowledge and contact-mechanics in a non-human primate?

Human toddlers demonstrate striking failures when searching for hidden objects that interact with other objects, yet successfully locate hidden objects that do not undergo mechanical interactions. This pattern hints at a developmental dissociation between contact-mechanical and spatiotemporal knowledge. Recent studies suggest that adult non-human primates may exhibit a similar dissociation. Here, I provide the first direct test of this dissociation using a search paradigm with adult rhesus monkeys. Subjects watched as a plum rolled behind one of two opaque barriers. In Experiment 1, subjects had to locate the plum based on the position of a wall that blocked the plum's trajectory. Subjects searched incorrectly, apparently neglecting information about the location of the wall. However, subjects searched correctly in Experiments 2-4 when they were given spatiotemporal information about the plum's movement. Results indicate that adult monkeys use spatiotemporal information, but not contact-mechanical information, to locate hidden objects. This dissociation between contact-mechanical and spatiotemporal knowledge is discussed in light of developmental theories of core knowledge and the literature on object-based attention in human adults.

Animals↗
PubMed2003

Representing tools: how two non-human primate species distinguish between the functionally relevant and irrelevant features of a tool.

Few studies have examined whether non-human tool-users understand the properties that are relevant for a tool's function. We tested cotton-top tamarins (Saguinus oedipus) and rhesus macaques (Macaca mulatta) on an expectancy violation procedure designed to assess whether these species make distinctions between the functionally relevant and irrelevant features of a tool. Subjects watched an experimenter use a tool to push a grape down a ramp, and then were presented with different displays in which the features of the original tool (shape, color, orientation) were selectively varied. Results indicated that both species looked longer when a newly shaped stick acted on the grape than when a newly colored stick performed the same action, suggesting that both species perceive shape as a more salient transformation than color. In contrast, tamarins, but not rhesus, attended to changes in the tool's orientation. We propose that some non-human primates begin with a predisposition to attend to a tool's shape and, with sufficient experience, develop a more sophisticated understanding of the features that are functionally relevant to tools.

Animals↗
PubMed2002

Object individuation using property/kind information in rhesus macaques (Macaca mulatta).

Around 1 year of age, infants develop the ability to individuate objects in the absence of spatiotemporal information. Some have proposed that this capacity relies on the emergence of language and, in particular, that comprehending an object's label is required to individuate it as a particular kind. One approach to testing this hypothesis is to conduct experiments on pre-linguistic human infants. A second is to test non-linguistic animals. We followed the second approach, exploring whether semi-free-ranging rhesus macaques can individuate objects using property/kind information. To make the results most directly comparable, we adapted a reaching paradigm used to examine property/kind individuation in infants. Results from three experiments demonstrate that, like 12-month-old infants, adult rhesus macaques can use both spatiotemporal and property/kind information to individuate food objects. In a fourth experiment designed to examine which properties are used to individuate food objects, results revealed that rhesus use color, but not shape. These results, together with experiments involving different procedures, provide support for the conclusion that in the absence of linguistic abilities, some non-human primates spontaneously use property/kind information to individuate objects.

Animals↗