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.     

The comparative psychology of same-different judgments by humans (Homo sapiens) and monkeys (Macaca mulatta)

The authors compared the performance of humans and monkeys in a Same-Different task. They evaluated the hypothesis that for humans the Same-Different concept is qualitative, categorical, and rule-based, so that humans distinguish 0-disparity pairs (i.e., same) from pairs with any discernible disparity (i.e., different); whereas for monkeys the Same-Different concept is quantitative, continuous, and similarity-based, so that monkeys distinguish small-disparity pairs (i.e., similar) from pairs with a large disparity (i.e., dissimilar). The results supported the hypothesis. Monkeys, more than humans, showed a gradual transition from same to different categories and an inclusive criterion for responding Same. The results have implications for comparing Same-Different performances across species--different species may not always construe or perform even identical tasks in the same way. In particular, humans may especially apply qualitative, rule-based frameworks to cognitive tasks like Same-Different.     

Mechanisms of inferential order judgments in humans (Homo sapiens) and rhesus monkeys (Macaca mulatta)

If A > B, and B > C, it follows logically that A > C. The process of reaching that conclusion is called transitive inference (TI). Several mechanisms have been offered to explain transitive performance. Scanning models claim that the list is scanned from the ends of the list inward until a match is found. Positional discrimination models claim that positional uncertainty accounts for accuracy and reaction time patterns. In Experiment 1, we trained rhesus monkeys (Macaca mulatta) and humans (Homo sapiens) on adjacent pairs (e.g., AB, BC, CD, DE, EF) and tested them with previously untrained nonadjacent pairs (e.g., BD). In Experiment 2, we trained a second list and tested with nonadjacent pairs selected between lists (e.g., B from List 1, D from List 2). We then introduced associative competition between adjacent items in Experiment 3 by training 2 items per position (e.g., B?C?, B?C?) before testing with untrained nonadjacent items. In all 3 experiments, humans and monkeys showed distance effects in which accuracy increased, and reaction time decreased, as the distance between items in each pair increased (e.g., BD vs. BE). In Experiment 4, we trained adjacent pairs with separate 9- and 5-item lists. We then tested with nonadjacent pairs selected between lists to determine whether list items were chosen according to their absolute position (e.g., D, 5-item list > E, 9-item list), or their relative position (e.g., D, 5-item list < E, 9-item list). Both monkeys' and humans' choices were most consistent with a relative positional organization.     

Retrospective and prospective metacognitive judgments in rhesus macaques (Macaca mulatta)

A growing body of research suggests that some non-human animals are capable of making accurate metacognitive judgments. In previous studies, non-human animals have made either retrospective or prospective judgments (about how they did on a test or how they will do on a test, respectively). These two types of judgments are dissociable in humans. The current study tested the abilities of two rhesus macaque monkeys to make both retrospective and prospective judgments about their performance on the same memory task. Both monkeys had been trained previously to make retrospective confidence judgments. Both monkeys successfully demonstrated transfer of retrospective metacognitive judgments to the new memory task. Furthermore, both monkeys transferred their retrospective judgments to the prospective task (one, immediately, and one, following the elimination of a response bias). This study is the first to demonstrate both retrospective and prospective monitoring abilities in the same monkeys and on the same task, suggesting a greater level of flexibility in animals’ metacognitive monitoring abilities than has been reported previously.     

Transfer of metacognitive skills and hint seeking in monkeys

Metacognition is knowledge that can be expressed as confidence judgments about what one knows (monitoring) and by strategies for learning what one does not know (control). Although there is a substantial literature on cognitive processes in animals, little is known about their metacognitive abilities. Here we show that rhesus macaques, trained previously to make retrospective confidence judgments about their performance on perceptual tasks, transferred that ability immediately to a new perceptual task and to a working memory task. We also show that monkeys can learn to request "hints" when they are given problems that they would otherwise have to solve by trial and error. This study demonstrates, for the first time, that nonhuman primates share with humans the ability to monitor and transfer their metacognitive ability both within and between different cognitive tasks, and to seek new knowledge on a need-to-know basis.     

Monkeys (Macaca mulatta and Cebus apella) track, enumerate, and compare multiple sets of moving items

Despite many demonstrations of numerical competence in nonhuman animals, little is known about how well animals enumerate moving stimuli. In this series of experiments, rhesus monkeys (Macaca mulatta) and capuchin monkeys (Cebus apella) performed computerized tasks in which they had to enumerate sets of stimuli. In Experiment 1, rhesus monkeys compared two sets of moving stimuli. Experiment 2 required comparisons of a moving set and a static set. Experiment 3 included human participants and capuchin monkeys to assess all 3 species' performance and to determine whether responding was to the numerical properties of the stimulus sets rather than to some other stimulus property such as cumulative area. Experiment 4 required both monkey species to enumerate subsets of each moving array. In all experiments, monkeys performed above chance levels, and their responses were controlled by the number of items in the arrays as opposed to nonnumerical stimulus dimensions. Rhesus monkeys performed comparably to adult humans when directly compared although capuchin performance was lower.     

Impaired performance from brief social isolation of rhesus monkeys (Macaca mulatta): a multiple video-task assessment

Social isolation has been demonstrated to produce profound and lasting psychological effects in young primates. In the present investigation, two adult rhesus monkeys (Macaca mulatta) were isolated from one another for up to 6 days and tested on 7 video tasks designed to assess psychomotor and cognitive functioning. Both the number and the quality (i.e., speed and accuracy) of responses were significantly compromised in the social isolation condition relative to levels in which the animals were tested together. It is argued that adult rhesus are susceptible to performance disruption by even relatively brief social isolation, and that these effects can best be assessed by a battery of complex and sensitive measures.     

Rhesus monkeys lack a consistent peak-end effect

In humans, the order of receiving sequential rewards can significantly influence the overall subjective utility of an outcome. For example, people subjectively rate receiving a large reward by itself significantly higher than receiving the same large reward followed by a smaller one (Do, Rupert, & Wolford, 2008). This result is called the peak-end effect. A comparative analysis of order effects can help determine the generality of such effects across primates, and we therefore examined the influence of reward-quality order on decision making in three rhesus macaque monkeys (Macaca mulatta). When given the choice between a high-low reward sequence and a low-high sequence, all three monkeys preferred receiving the high-value reward first. Follow-up experiments showed that for two of the three monkeys their choices depended specifically on reward-quality order and could not be accounted for by delay discounting. These results provide evidence for the influence of outcome order on decision making in rhesus monkeys. Unlike humans, who usually discount choices when a low-value reward comes last, rhesus monkeys show no such peak-end effect.     

Human factors with nonhumans: factors that affect computer-task performance

There are two general strategies that may be employed for "doing human factors research with nonhuman animals." First, one may use the methods of traditional human factors investigations to examine the nonhuman animal-to-machine interface. Alternatively, one might use performance by nonhuman animals as a surrogate for or model of performance by a human operator. Each of these approaches is illustrated with data in the present review. Chronic ambient noise was found to have a significant but inconsequential effect on computer-task performance by rhesus monkeys (Macaca mulatta). Additional data supported the generality of findings such as these to humans, showing that rhesus monkeys are appropriate models human psychomotor performance. It is argued that ultimately the interface between comparative psychology and technology will depend on the coordinated use of both strategies of investigation.     

Recognizing facial cues: individual discrimination by chimpanzees (Pan troglodytes) and rhesus monkeys (Macaca mulatta)

Faces are one of the most salient classes of stimuli involved in social communication. Three experiments compared face-recognition abilities in chimpanzees (Pan troglodytes) and rhesus monkeys (Macaca mulatta). In the face-matching task, the chimpanzees matched identical photographs of conspecifics' faces on Trial 1, and the rhesus monkeys did the same after 4 generalization trials. In the individual-recognition task, the chimpanzees matched 2 different photographs of the same individual after 2 trials, and the rhesus monkeys generalized in fewer than 6 trials. The feature-masking task showed that the eyes were the most important cue for individual recognition. Thus, chimpanzees and rhesus monkeys are able to use facial cues to discriminate unfamiliar conspecifics. Although the rhesus monkeys required many trials to learn the tasks, this is not evidence that faces are not as important social stimuli for them as for the chimpanzees.     

Rhesus monkeys lack a consistent peak-end effect

In humans, the order of receiving sequential rewards can significantly influence the overall subjective utility of an outcome. For example, people subjectively rate receiving a large reward by itself significantly higher than receiving the same large reward followed by a smaller one (Do, Rupert, & Wolford, 2008). This result is called the peak-end effect. A comparative analysis of order effects can help determine the generality of such effects across primates, and we therefore examined the influence of reward-quality order on decision making in three rhesus macaque monkeys (Macaca mulatta). When given the choice between a high–low reward sequence and a low–high sequence, all three monkeys preferred receiving the high-value reward first. Follow-up experiments showed that for two of the three monkeys their choices depended specifically on reward-quality order and could not be accounted for by delay discounting. These results provide evidence for the influence of outcome order on decision making in rhesus monkeys. Unlike humans, who usually discount choices when a low-value reward comes last, rhesus monkeys show no such peak-end effect.     

Attentional biases and memory for emotional stimuli in men and male rhesus monkeys

We examined attentional biases for social and non-social emotional stimuli in young adult men and compared the results to those of male rhesus monkeys (Macaca mulatta) previously tested in a similar dot-probe task (King et al. in Psychoneuroendocrinology 37(3):396–409, 2012). Recognition memory for these stimuli was also analyzed in each species, using a recognition memory task in humans and a delayed non-matching-to-sample task in monkeys. We found that both humans and monkeys displayed a similar pattern of attentional biases toward threatening facial expressions of conspecifics. The bias was significant in monkeys and of marginal significance in humans. In addition, humans, but not monkeys, exhibited an attentional bias away from negative non-social images. Attentional biases for social and non-social threat differed significantly, with both species showing a pattern of vigilance toward negative social images and avoidance of negative non-social images. Positive stimuli did not elicit significant attentional biases for either species. In humans, emotional content facilitated the recognition of non-social images, but no effect of emotion was found for the recognition of social images. Recognition accuracy was not affected by emotion in monkeys, but response times were faster for negative relative to positive images. Altogether, these results suggest shared mechanisms of social attention in humans and monkeys, with both species showing a pattern of selective attention toward threatening faces of conspecifics. These data are consistent with the view that selective vigilance to social threat is the result of evolutionary constraints. Yet, selective attention to threat was weaker in humans than in monkeys, suggesting that regulatory mechanisms enable non-anxious humans to reduce sensitivity to social threat in this paradigm, likely through enhanced prefrontal control and reduced amygdala activation. In addition, the findings emphasize important differences in attentional biases to social versus non-social threat in both species. Differences in the impact of emotional stimuli on recognition memory between monkeys and humans will require further study, as methodological differences in the recognition tasks may have affected the results.     

Exploration of virtual mazes by rhesus monkeys (<Emphasis Type="Italic">Macaca mulatta</Emphasis>)

A chasm divides the huge corpus of maze studies found in the literature, with animals tested in mazes on the one side and humans tested with mazes on the other. Advances in technology and software have made possible the production and use of virtual mazes, which allow humans to navigate computerized environments and thus for humans and nonhuman animals to be tested in comparable spatial domains. In the present experiment, this comparability is extended even further by examining whether rhesus monkeys (Macaca mulatta) can learn to explore virtual mazes. Four male macaques were trained to manipulate a joystick so as to move through a virtual environment and to locate a computer-generated target. The animals succeeded in learning this task, and located the target even when it was located in novel alleys. The search pattern within the maze for these animals resembled the pattern of maze navigation observed for monkeys that were tested on more traditional two-dimensional computerized mazes.     

Ultra-rapid categorisation in non-human primates

The visual system of primates is remarkably efficient for analysing information about objects present in complex natural scenes. Recent work has demonstrated that they perform this at very high speeds. In a choice saccade task, human subjects can initiate a first reliable saccadic eye movement response to a target (the image containing an animal) in only 120 ms after image onset. Such fast responses impose severe time constraints if one considers neuronal responses latencies in high-level ventral areas of the macaque monkey. The question then arises: are non-human primates able to perform the task? Two rhesus macaque monkeys (Macaca mulatta) were trained to perform the same forced-choice categorization task as the one used in humans. Both animals performed the task with a high accuracy and generalized to new stimuli that were introduced everyday: accuracy levels were comparable both with new and well-known images (84% vs. 94%). More importantly, reaction times were extremely fast (minimum reaction time 100 ms and median reaction time 152 ms). Given that typical single units onset times in Inferotemporal cortex (IT) are about as long as the shortest behavioural responses measured here, we conclude that visual processing involved in ultra rapid categorisations might be based on rather simple shape cue analysis that can be achieved in areas such as extrastriate cortical area V4. The present paper demonstrates for the first time, that rhesus macaque monkeys (Macaca mulatta) are able to match human performance in a forced-choice saccadic categorisation task of animals in natural scenes.     

Game-like tasks for comparative research: Leveling the playing field

Game-like computer tasks offer many benefits for psychological research. In this paper, the usefulness of such tasks to bridge population differences (e.g., age, intelligence, species) is discussed and illustrated. A task called ALVIN was used to assess humans’ and monkeys’ working memory for sequences of colors with or without tones. Humans repeated longer lists than did the monkeys, and only humans benefited when the visual stimuli were accompanied by auditory cues. However, the monkeys did recall sequences at levels comparable to those reported elsewhere for children. Comparison of similarities and differences between the species is possible because the two groups were tested with exactly the same game-like paradigm.     

Extensive practice does not eliminate human switch costs

Numerous human task-switching studies have shown that decision making that follows a task switch is slower and less accurate than that which follows a task repetition. Stoet and Snyder (2003a) tested humans and rhesus monkeys on a task-switching paradigm, but found, surprisingly, no switch costs in the monkeys. We hypothesized that the exceptional monkey behavior may have been due to the more extensive practice the monkeys received in comparison with human subjects. In the present study, we tested the hypothesis that extensive practice can abolish switch costs in humans. Four human subjects each performed 23,000 trials in a task-switching paradigm. We found that this amount of practice does not abolish switch costs.     

Stroop-like effects for monkeys and humans: processing speed or strength of association?

Abstract— Stroop-like effects have been found using a variety of paradigms and subject groups In the present investigation, 6 rhesus monkeys (Macaca mulatta) and 28 humans exhibited Stroop-like inserference and facilitation in a relativenumerousness task Monkeys, like humans, processed the meanings of the numerical symbols automatically—despite the fact that these meanings were irrelevant to task performance These data also afforded direct comparison of interpretations of the Stroop effect in terms of processing speed versus association strength These findings were consistent with parallel-processing models of Stroop-like interference proposed elsewhere, but not with processing-speed accounts posited frequently to explain the effect     

Asymmetrical hand use in rhesus monkeys (Macaca mulatta) in tactually and visually regulated tasks

Asymmetrical hand use by rhesus monkeys (Macaca mulatta) was investigated in a series of tactually and visually guided tasks. The 1st experiment recorded manual preferences of 29 monkeys for solving a haptic discrimination task in a hanging posture. There was a left-hand population bias: 21 monkeys had a left-hand bias, 4 a right-hand bias, and 4 no bias. The 2nd experiment, 4 tasks with 23 to 51 monkeys, investigated the critical components of the 1st experiment by varying the posture (hanging, sitting, or tripedal) and the sensory requirements (tactile or visual). Posture influenced hand bias, with a population-level left-hand bias in hanging and sitting postures, but an almost symmetrical distribution in the tripedal posture. A left-hand bias was found for both sensory modalities, but the bias was stronger in the tactual tasks. Results suggest a possible right-hemisphere specialization in the rhesus for tactile, visual, or spatial processing.     

Sequential responding and planning in capuchin monkeys (Cebus apella)

Previous experiments have assessed planning during sequential responding to computer generated stimuli by Old World nonhuman primates including chimpanzees and rhesus macaques. However, no such assessment has been made with a New World primate species. Capuchin monkeys (Cebus apella) are an interesting test case for assessing the distribution of cognitive processes in the Order Primates because they sometimes show proficiency in tasks also mastered by apes and Old World monkeys, but in other cases fail to match the proficiency of those other species. In two experiments, eight capuchin monkeys selected five arbitrary stimuli in distinct locations on a computer monitor in a learned sequence. In Experiment 1, shift trials occurred in which the second and third stimuli were transposed when the first stimulus was selected by the animal. In Experiment 2, mask trials occurred in which all remaining stimuli were masked after the monkey selected the first stimulus. Monkeys made more mistakes on trials in which the locations of the second and third stimuli were interchanged than on trials in which locations were not interchanged, suggesting they had already planned to select a location that no longer contained the correct stimulus. When mask trials occurred, monkeys performed at levels significantly better than chance, but their performance exceeded chance levels only for the first and the second selections on a trial. These data indicate that capuchin monkeys performed very similarly to chimpanzees and rhesus monkeys and appeared to plan their selection sequences during the computerized task, but only to a limited degree.     

Behavioral asymmetries of psychomotor performance in rhesus monkeys (Macaca mulatta): a dissociation between hand preference and skill.

Hand preferences were recorded for 35 rhesus monkeys (Macaca mulatta) as they manipulated a joystick in response to 2 computerized tasks. These preferences were then used to contrast 8 left- and 10 right-handed subjects on performance measures of hand skill. Individual hand preferences were found, but no significant population asymmetry was observed across the sample. However, the performance data reveal substantial benefits of right-handedness for joystick manipulation, as this group of monkeys mastered the 2 psychomotor tasks significantly faster than did their left-handed counterparts. The data support earlier reports of a right-hand advantage for joystick manipulation and also support the importance of distinguishing between hand preference and manual performance in research on functional asymmetries.