Rhesus monkeys (macaca mulatta) immediately generalize the uncertain response.

Rhesus monkeys (Macaca mulatta) have learned, like humans, to use an uncertain response adaptively under test conditions that create uncertainty, suggesting a metacognitive process by which human and nonhuman primates may monitor their confidence and alter their behavior accordingly. In this study, 4 rhesus monkeys generalized their use of the uncertain response, without additional training, to 2 familiar tasks (2-choice discrimination learning and mirror-image matching to sample) that predictably and demonstrably produce uncertainty. The monkeys were significantly less likely to use the uncertain response on trials in which the answer might be known. These results indicate that monkeys, like humans, know when they do not know and that they can learn to use a symbol as a generalized means for indicating their uncertainty. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rhesus monkeys (Macaca mulatta) hear rising frequency sounds as looming.

Rising sound intensity provides an important cue for the detection of looming objects. Studies with humans indirectly suggest that rising pitch can also signal a looming object. This link between rising intensity and rising frequency is puzzling because no physical rise in frequency occurs when a sound source approaches. Putative explanations include (a) the idea that the loudness of sound depends on its frequency, (b) the frequent co-occurrence of rising intensity with rising frequency in vocalizations generates an association between the 2 features, and (c) auditory neurons process amplitude- and frequency-modulated sounds similarly. If these hypotheses are valid, then rhesus monkeys (Macaca mulatta)—which share some homologies in the vocal production apparatus and auditory system—should also associate rising frequency with rising intensity, and thus should perceive rising frequency as a looming sound source. A head-turning assay and a preferential-looking paradigm revealed that monkeys show an attentional bias toward rising versus falling frequency sounds and link the former to visual looming signals. This suggests that monkeys hear a rising frequency sound as a looming sound source even though, in the real world, no such link exists. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Salience of Caller Identity in Rhesus Monkey (Macaca mulatta) Coos and Screams: Perceptual Experiments With Human (Homo sapiens) Listeners.

Recent evidence from acoustic analysis and playback experiments indicates that adult female rhesus monkey (Macaca mulatta) coos are individually distinctive but their screams are not. In this study, the authors compared discrimination of individual identity in these sounds by naive human listeners who judged whether 2 sounds had been produced by the same monkey or 2 monkeys. Each of 3 experiments using this same-different design showed significantly better discrimination of vocalizer identity from coos than from screams. Experiment 1 demonstrated the basic finding. Experiment 2 also tested the effect of non-identity-related scream variation, and Experiment 3 added a comparison with human vowel sounds. Outcomes suggest that acoustic structural differences in coos and screams influence salience of caller-identity cues, with significant implications for understanding the functions of these calls. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social competence is reduced in socially deprived rhesus monkeys (Macaca mulatta).

Rhesus monkeys deprived for some period from their mother have often served as a model for the effect of adverse rearing conditions on social competence in humans. Social competence is the capacity to react in a species-specific way to social interactions. The current study assesses whether early deprivation from peers also affects the rates of behavior and social competence in rhesus monkeys. This was studied in groups of rhesus monkeys with different rearing conditions: subadult females that were mother-only reared during their first year of life and subsequently housed with peers were compared with subadult females from five naturalistic social groups. Socially deprived monkeys showed higher rates of submission and stereotypic behaviors than socially reared individuals. In addition, they show socially incompetent behavior, since they react with agonistic behavior to nonthreatening social situations. The results suggest that this socially incompetent behavior is rooted in a general feeling of anxiety toward group companions. The authors hypothesize that anxiety negatively affects social information processing, which results in socially incompetent behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Configural processing and face viewpoint.

Configural/holistic processing, a key property of face recognition, has previously been examined only for front views of faces. Here, 6 experiments tested front (0°), three-quarter (45°), and profile views (90°), using composite and peripheral inversion tasks. Results showed an overall disadvantage in identifying profiles. This arose entirely from part-based processing: View effects were as strong for disrupted-configuration faces (inverted, misaligned, scrambled) as for normal-configuration faces. In contrast, configural processing (aligned-misaligned difference, upright-inverted difference) was equally strong for all views under both clear and degraded viewing conditions. Findings argue that, although part-based processing is weakened by lower natural frequency of the profile view and/or occlusion of key face features, neither of these variables influences configural processing. This suggests that the functional role of configural processing is to allow reliable face identification despite substantial variance in local information across different natural images. Results also show that only image-plane rotation of faces (upright through inverted) affects configural processing; the contrast with depth rotation has potential implications for understanding the origin of configural processing in terms of innate versus experience-based expertise contributions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rhesus Macaques (Macaca mulatta) Categorize Unknown Conspecifics According to Their Dominance Relations.

The authors trained 3 adult male rhesus macaques (Macaca mulatta) to categorize pairs of unknown conspecifics presented in a video according to the dominance status of the videotaped monkeys. The subjects were trained to choose the dominant monkey for a category of films (e.g., films showing 1 monkey chasing another); then, new films were presented involving different conspecifics, and the monkeys' first responses to this new category of behavior (e.g., monkeys fighting) were taken as evidence of transfer. Two subjects were able to generalize categorical judgments of dominance to new films involving new behaviors. These findings seem to indicate that monkeys can use abstract social concepts and are aware of the social relationships within their group. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rhesus macaques (Macaca mulatta) as living fossils of hominoid personality and subjective well-being.

Personality dimensions capturing individual differences in behavior, cognition, and affect have been described in several species, including humans, chimpanzees, and orangutans. However, comparisons between species are limited by the use of different questionnaires. We asked raters to assess free-ranging rhesus macaques at two time points on personality and subjective well-being questionnaires used earlier to rate chimpanzees and orangutans. Principal-components analysis yielded domains we labeled Confidence, Friendliness, Dominance, Anxiety, Openness, and Activity. The presence of Openness in rhesus macaques suggests it is an ancestral characteristic. The absence of Conscientiousness suggests it is a derived characteristic in African apes. Higher Confidence and Friendliness, and lower Anxiety were prospectively related to subjective well-being, indicating that the connection between personality and subjective well-being in humans, chimpanzees, and orangutans is ancestral in catarrhine primates. As demonstrated here, each additional species studied adds another fold to the rich, historical story of primate personality evolution. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Detection of directed gaze in rhesus monkeys (Macaca mulatta).

To examine the ability of monkeys to detect the direction of attention of other individuals, the authors quantitatively investigated the visual scanning pattern of rhesus monkeys (Macaca mulatta) in response to visually presented images of a human frontal face. The present results demonstrated not only that monkeys predominantly gaze at the eyes as compared with other facial areas in terms of duration and number of fixations, but also that they gaze at the eyes for a longer time period and more frequently when a human face, presented as a stimulus, gazed at them than when the gaze was shifted. These results indicate that rhesus monkeys are sensitive to the directed gaze of humans, suggesting that monkeys pay more attention to the human whose attention is directed to them. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sequential Responding and Planning in Chimpanzees (Pan troglodytes) and Rhesus Macaques (Macaca mulatta).

Chimpanzees (Pan troglodytes) and rhesus macaques (Macaca mulatta) selected either Arabic numerals or colored squares on a computer monitor in a learned sequence. On shift trials, the locations of 2 stimuli were interchanged at some point. More errors were made when this interchange occurred for the next 2 stimuli to be selected than when the interchange was for stimuli later in the sequence. On mask trials, all remaining stimuli were occluded after the 1st selection. Performance exceeded chance levels for only 1 selection after these masks were applied. There was no difference in performance for either stimulus type (numerals or colors). The data indicated that the animals planned only the next selection during these computerized tasks as opposed to planning the entire response sequence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Emergence of stereotypies in juvenile monkeys (Macaca mulatta) with neonatal amygdala or hippocampus lesions.

The emergence of stereotypies was examined in juvenile rhesus monkeys (Macaca mulatta) who, at 2 weeks of postnatal age, received selective bilateral ibotenic acid lesions of the amygdala (N = 8) or hippocampus (N = 8). The lesion groups were compared to age-matched control subjects that received a sham surgical procedure (N = 8). All subjects were maternally reared for the first 6 months and provided access to social groups throughout development. Pronounced stereotypies were not observed in any of the experimental groups during the first year of life. However, between 1 to 2 years of age, both amygdala- and hippocampus-lesioned subjects began to exhibit stereotypies. When observed as juveniles, both amygdala- and hippocampus-lesioned subjects consistently produced more stereotypies than the control subjects in a variety of contexts. More interesting, neonatal lesions of either the amygdala or hippocampus resulted in unique repertoires of repetitive behaviors. Amygdala-lesioned subjects exhibited more self-directed stereotypies and the hippocampus-lesioned subjects displayed more head-twisting. We discuss these results in relation to the neurobiological basis of repetitive stereotypies in neurodevelopmental disorders, such as autism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acute and chronic effects of ramelteon in rhesus monkeys (Macaca mulatta): Dependence liability studies.

The acute and chronic effects of ramelteon, an MT?/MT? receptor agonist, were evaluated in rhesus monkeys (Macaca mulatta) to assess discriminative stimulus effects in comparison with traditional benzodiazepine receptor agonists and to assess physical dependence potential. Discriminative effects of ramelteon were compared with midazolam in untreated monkeys and in diazepam-dependent monkeys that discriminated flumazenil. Dependence potential of ramelteon after daily 1-year administration (and intermittent discontinuation) was evaluated with standard operant procedures. Ramelteon did not produce benzodiazepine-like discriminative stimulus effects at doses up to 10 mg/kg. Long-term treatment or its discontinuation had no significant effect on spontaneous behavior, operant behavior, body weight, motor activity, or posture. These findings suggest that ramelteon is not likely to have benzodiazepine-like abuse or dependence liability. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Impairment of executive function induced by hypertension in the Rhesus monkey (Macaca mulatta).

The effects of chronic, untreated hypertension on executive function were investigated in a nonhuman primate model of hypertensive cerebrovascular disease. Executive function was assessed with the Conceptual Set-Shifting Task (CSST), a task adapted from the human Wisconsin Card Sorting Test (WCST). Like the WCST, the CSST requires abstraction of a stimulus set, followed by a series of set shifts. Performance on the CSST by 7 young adult monkeys (Macaca mulatta) with surgically induced hypertension was compared with that of 6 normotensive monkeys. The hypertensive group was significantly impaired relative to the normotensive group in abstraction and set shifting. Although the neural basis of this impairment is unclear, evidence from studies with humans and monkeys suggests that the prefrontal cortex may be the locus for this effect of hypertension. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Amygdalectomy and responsiveness to novelty in rhesus monkeys (Macaca mulatta): Generality and individual consistency of effects.

Rhesus monkeys (Macaca mulatta) with bilateral ibotenic acid-produced lesions of the amygdala were compared with controls in several novel situations, including exposures to metal objects, toy animals, and a person. Early in testing, the monkeys with lesions showed reduced inhibitions on responsiveness compared with controls. With continuing exposures, differences between groups diminished sharply as inhibitions waned in the controls. This outcome is consistent with the hypothesis that the amygdala mediates caution in initial reactions to ambiguous or threatening novel situations, which, in the absence of adverse consequences, diminishes with repetition. Consistency of individual responsiveness across different situations, including pairing with other monkeys, was substantial in lesioned and normal monkeys, suggesting that stable qualities of temperament influenced the results in both groups. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Turning configural processing upside down: Part and whole body postures.

Like faces, body postures are susceptible to an inversion effect in untrained viewers. The inversion effect may be indicative of configural processing, but what kind of configural processing is used for the recognition of body postures must be specified. The information available in the body stimulus was manipulated. The presence and magnitude of inversion effects were compared for body parts, scrambled bodies, and body halves relative to whole bodies and to corresponding conditions for faces and houses. Results suggest that configural body posture recognition relies on the structural hierarchy of body parts, not the parts themselves or a complete template match. Configural recognition of body postures based on information about the structural hierarchy of parts defines an important point on the configural processing continuum, between recognition based on first-order spatial relations and recognition based on holistic undifferentiated template matching. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Opioids and attachment in rhesus macaque (Macaca mulatta) abusive mothers.

This study investigated the role of the endogenous opioid system in maternal and affiliative behavior of group-living rhesus macaque (Macaca mularta) mothers with a history of abusive parenting. 18 mothers received an injection of the opioid antagonist naltrexone or saline for 5 days per wk for the first 4 wks of the infant's life. After treatment, mother-infant pairs were focally observed. Naltrexone did not significantly affect infant abuse or other measures of maternal behavior. Naltrexone increased the amount of grooming received by mothers from other group members and reduced the mothers' rate of displacement activities such as scratching, yawning, and self-grooming. These results concur with previous primate studies in suggesting that opioids mediate the rewarding effects of receiving grooming and affect anxiety-related behaviors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analogical reasoning and the differential outcome effect: Transitory bridging of the conceptual gap for rhesus monkeys (Macaca mulatta).

Monkeys, unlike chimpanzees and humans, have a marked difficulty acquiring relational matching-to-sample (RMTS) tasks that likely reflect the cognitive foundation upon which analogical reasoning rests. In the present study, rhesus monkeys (Macaca mulatta) completed a categorical (identity and nonidentity) RMTS task with differential reward (pellet ratio) and/or punishment (timeout ratio) outcomes for correct and incorrect choices. Monkeys in either differential reward-only or punishment-only conditions performed at chance levels. However, the RMTS performance of monkeys experiencing both differential reward and punishment conditions was significantly better than chance. Subsequently when all animals experienced nondifferential outcomes tests, their RMTS performance levels were at chance. These results indicate that combining differential reward and punishment contingencies provide an effective, albeit transitory, scaffolding for monkeys to judge analogical relations-between-relations. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Learning of discriminations is impaired, but generalization to altered views is intact, in monkeys (Macaca mulatta) with perirhinal cortex removal.

Rhesus monkeys (Macaca mulatta) were taught a large number of visual discriminations and then either received bilateral removal of the perirhinal cortex or were retained as unoperated controls. Operated monkeys were impaired in retention of the preoperatively learned problems. To test for generalization to novel views, the monkeys were required to discriminate, in probe trials, familiar pairs of images that were rotated, enlarged, shrunken, presented with color deleted, or degraded by masks. Although these manipulations reduced accuracy in both groups, the operated group was not differentially affected. In contrast, the same operated monkeys were impaired in reversal of familiar discriminations and in acquisition of new single-pair discriminations. These results indicate an important role for perirhinal cortex in visual learning, memory, or both, and show that under a variety of conditions, perirhinal cortex is not critical for the identification of stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prototype abstraction by monkeys (Macaca mulatta).

The authors analyze the shape categorization of rhesus monkeys (Macaca mulatta) and the role of prototype- and exemplar-based comparison processes in monkeys' category learning. Prototype and exemplar theories make contrasting predictions regarding performance on the Posner-Homa dot-distortion categorization task. Prototype theory--which presumes that participants refer to-be-categorized items to a representation near the category's center (the prototype)--predicts steep typicality gradients and large prototype-enhancement effects. Exemplar theory--which presumes that participants refer to-be-categorized items to memorized training exemplars-predicts flat typicality gradients and small prototype-enhancement effects. Across many categorization tasks that, for the first time, assayed monkeys' dot-distortion categorization, monkeys showed steep typicality gradients and large prototype-enhancement effects. These results suggest that monkeys--like humans--refer to-be-categorized items to a prototype-like representation near the category's center rather than to a set of memorized training exemplars. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The expression of social dominance following neonatal lesions of the amygdala or hippocampus in rhesus monkeys (Macaca mulatta).

As part of ongoing studies on the neurobiology of socioemotional behavior in the nonhuman primate, the authors examined the social dominance hierarchy of juvenile macaque monkeys (Macaca mulatta) that received bilateral ibotenic acid lesions of the amygdala or the hippocampus or a sham surgical procedure at 2 weeks of age. The subjects were reared by their mothers with daily access to large social groups. Behavioral observations were conducted while monkeys were given access to a limited preferred food. This testing situation reliably elicited numerous species-typical dominance behaviors. All subjects were motivated to retrieve the food when tested individually. However, when a group of 6 monkeys was given access to only 1 container of the preferred food, the amygdala-lesioned monkeys had less frequent initial access to the food, had longer latencies to obtain the food, and demonstrated fewer species-typical aggressive behaviors. They were thus lower ranking on all indices of social dominance. The authors discuss these findings in relation to the role of the amygdala in the establishment of social rank and the regulation of aggression and fear. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Can monkeys (Macaca mulatta) represent invisible displacement?

Four experiments were conducted to assess whether or not rhesus macaques (Macaca mulatta) could represent the unperceived movements of a stimulus. Subjects were tested on 2 computerized tasks, HOLE (monkeys) and LASER (humans and monkeys), in which subjects needed to chase or shoot at, respectively, a moving target that either remained visible or became invisible for a portion of its path of movement. Response patterns were analyzed and compared between target-visible and target-invisible conditions. Results of Experiments 1, 2, and 3 demonstrated that the monkeys are capable of extrapolating movement. That this extrapolation involved internal representation of the target's invisible movement was suggested but not confirmed. Experiment 4, however, demonstrated that the monkeys are capable of representing the invisible displacements of a stimulus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)