Reverse-reward learning in squirrel monkeys (Saimiri sciureus): retesting after 5 years, and assessment on qualitative transfer

Seven squirrel monkeys (Saimiri sciureus) previously trained on reverse-reward tasks were presented with the original "1-versus-4" task after a 5-year interval without reverse-reward experience (Experiment 1). None of them reliably selected the smaller food array; however, at around chance level, their performance was superior to when they were first exposed to the task almost 6 years previously, suggesting some long-term memory retention. One naive monkey consistently selected the larger array, as expected. In Experiment 2, trials consisting of 1 versus 1 piece of two qualitatively different types of food were interspersed among familiar 1-versus-4 trials. None of five monkeys tested reliably selected the less-preferred food to get the more preferred food as the reward, and one monkey scored below chance. However, when one piece of low-preference food was paired with four pieces of high-preference food (Experiment 3), all four monkeys tested avoided reaching for the latter and thereby obtained it as the reward; two monkeys obtained perfect scores on these trials. These two monkeys were trained on a specific qualitative reverse-reward pairing and then again tested on new pairings (Experiment 4), but transfer was incomplete. Compound trials that pit quantity against quality in novel ways appear taxing for squirrel monkeys, despite competence in reverse-reward on both dimensions separately.     

The effect of choice of exercise mode on psychological responses

Objectives: Choice has been linked to both motivation and psychological responses to exercise. This paper investigates participants’ psychological responses when they completed an exercise session where there was a high-preference exercise mode as opposed to a low-preference exercise mode. High- and low-preference were established by participants indicating their preferred choice of exercise from three standard modes used for aerobic work.Method: Participants were 20 low-active adults who exercised for 20 min on each mode of exercise (high-preference versus low-preference). Affect, ratings of perceived exertion (RPE) and heart rate (HR) were recorded every 5 min during exercise, and affect and HR were assessed pre-exercise and 5 min post-exercise.Results: Repeated measures analysis of variance revealed condition and time main effects for affect sub-scales and RPE and a time main effect for HR. Affect sub-scales, RPE and HR generally increased over time. RPE, Fatigue and Psychological Distress were higher in the low-preference condition and positive well-being was higher in the high-preference condition.Conclusions: Affect and RPE were influenced by the preferred choice manipulation. Affect was more positive, and RPE lower, in the high-preference versus low-preference condition while work rate remained constant across conditions.     

Antecedent effects of observing peer play

The relative reinforcing value of toys was assessed in the absence of, and immediately following, participant observation of a peer manipulating one of the toys. Preference assessments were used to identify preference hierarchies. Reinforcer assessments were conducted with a high-preference item, a low-preference item, and a control. Each participant allocated responding toward the high-preference item during baseline. When reinforcer assessment sessions were preceded by a peer observation period, 3 of the 4 participants shifted allocation to the toy manipulated by the peer. The 4th participant shifted allocation only when the high-preference stimulus was replaced with a medium-preference stimulus. These data suggest that, among preschoolers, response allocation is influenced by observations of peers playing.     

Effects of deprivation on engagement in preferred activities by persons with developmental disabilities

This study examined the effects of deprivation on engagement in activities for 3 adult men with developmental disabilities. First, an assessment was conducted to identify a high- and a low-preference activity for each participant. Second, the high-preference activity was made available following three amounts of deprivation of the activity (15 min, 2 hr, and 1 to 4 days); the low-preference activity was made available following the schedule of deprivation that produced the highest level of engagement by each participant in the high-preference activity. The results were that 1 to 4 days of deprivation produced the highest average amounts of engagement in the high-preference activity for each participant; this amount of deprivation did not produce high engagement in the low-preference activities. Third, the deprivation procedures and results were replicated when high-preference activities were presented by teachers during the participants' daily activities when their engagement had been quite low.     

Evaluation of absolute and relative reinforcer value using progressive-ratio schedules

We evaluated behavior exhibited by individuals with developmental disabilities using progressive-ratio (PR) schedules. High- and low-preference stimuli were determined based on the results of a paired-stimulus preference assessment and were evaluated in subsequent reinforcer and PR assessments using concurrent and single schedules of presentation. In Experiment 1, results showed that for 2 of 3 participants, stimuli determined to be low-preference functioned as reinforcers when evaluated independent of high-preference stimuli. Further, the results from Experiment 2 showed that low-preference stimuli also functioned as reinforcers under gradually increasing PR requirements. Results suggest that for cases in which a high-preference stimulus is unavailable or impractical, the contingent delivery of relatively less preferred stimuli may maintain appropriate behavior, even as schedule requirements increase.     

Socially learned preferences for differentially rewarded tokens in the brown capuchin monkey (Cebus apella)

Social learning is assumed to underlie traditions, yet evidence indicating social learning in capuchin monkeys (Cebus apella), which exhibit traditions, is sparse. The authors tested capuchins for their ability to learn the value of novel tokens using a previously familiar token-exchange economy. Capuchins change their preferences in favor of a token worth a high-value food reward after watching a conspecific model exchange 2 differentially rewarded tokens, yet they fail to develop a similar preference after watching tokens paired with foods in the absence of a conspecific model. They also fail to learn that the value of familiar tokens has changed. Information about token value is available in all situations, but capuchins seem to pay more attention in a social situation involving novel tokens.     

Monkeys fail to reciprocate in an exchange task

Exchanges form the basis of human economies. Animals too can engage in reciprocal interactions but they do not barter goods like humans, which raises the question of the abilities necessary for trading to occur. Previous studies have shown that non-human primates can exchange food with human partners. Here, we tested the ability of brown capuchin monkeys and Tonkean macaques to reciprocate in a task requiring two conspecifics to exchange tokens in order to obtain rewards from an experimenter. We recorded 56 transfers between subjects in capuchin monkeys and 10 in Tonkean macaques. All transfers were passive in both species. Capuchins preferentially picked up tokens valuable for them in the partner’s compartment. They tended to manipulate the partner-valued tokens more often than the no-value ones, leading to more opportunities for these tokens to end up within reach of the partner. Despite optimal conditions where values of goods were defined and known by partners, however, none of the pairs tested engaged in short-term reciprocal interactions. These results indicate that calculated reciprocity was difficult if not impossible in the animals tested.     

Multi-stage mental process for economic choice in capuchins

We studied economic choice behavior in capuchin monkeys by offering them to choose between two different foods available in variable amounts. When monkeys selected between familiar foods, their choice patterns were well-described in terms of relative value of the two foods. A leading view in economics and biology is that such behavior results from stimulus-response associations acquired through experience. According to this view, values are not psychologically real; they can only be defined a posteriori. One prediction of this associative model is that animals faced for the first time with a new pair of foods learn to choose between them gradually. We tested this prediction. Surprisingly, we find that monkeys choose as effectively between new pairs of foods as they choose between familiar pairs of foods. We therefore, propose a cognitive model in which economic choice results from a two-stage mental process of value-assignment and decision-making. In a follow-up experiment, we find that the relative value assigned to three foods in sessions in which we tested them against each other combine according to transitivity.     

Concept learning by monkeys with video picture images and a touch screen.

Two rhesus monkeys were trained in a same/different task to discriminate digitized computer-stored picture stimuli. The pictures were digitized from 35-mm slides and presented in pairs on a computer monitor. The monkeys were required to touch the pictures and then make a choice response to indicate whether the pictures were identical or nonidentical. The response areas and stimuli were located to the sides of the picture stimuli. Responses were defined and monitored by an infrared matrix touch screen. After learning the same/different task, both monkeys showed performance accuracy with novel picture stimuli similar to that with training picture stimuli. This accurate novel-picture transfer indicates that a same/different concept had been learned, a concept similar to the one they had previously demonstrated in a different apparatus with rear-projected slide stimuli and a response lever.     

Rhesus monkeys (Macaca mulatta) demonstrate robust memory for what and where,but not when,in an open-field test of memory

We adapted a paradigm developed by Clayton and Dickinson (1998), who demonstrated memory for what, where, and when in scrub jays, for use with rhesus monkeys. In the study phase of each trial, monkeys found a preferred and a less-preferred food reward in a trial-unique array of three locations in a large room. After 1 h, monkeys returned to the test room, where they found foods placed as during study. Twenty-five hours after the study phase monkeys again searched the room, but now the preferred food was replaced with a distasteful food remnant, while the less-preferred food was still present. Although monkeys remembered the locations of the foods for up to 25 h, they did not learn that the preferred food was available after the short, but not after the long delay. Thus, monkeys demonstrated long-term memory for the type and location of food but failed to demonstrate sensitivity to when they acquired that knowledge.     

Visual preferences for sex and status in female rhesus macaques

Most primates are both highly visual and highly social. These qualities predict that visual cues to social variables, such as identity, sex, social status, and reproductive quality, would be intrinsically valuable and systematically attract attention. Supporting this idea, thirsty male rhesus macaques (Macaca mulatta) will forego fluid reward to view images of the faces of high-ranking males and the sexual skin of females. Whether female rhesus macaques, who experience dramatically different social pressures and reproductive costs than male macaques, also systematically and spontaneously value visual cues to social information remains untested experimentally. We probed the preferences of female rhesus macaques, given the opportunity to display an image from a known class of social stimuli or touch a second target to display a blank screen. We found that females preferred faces of high-status males and also images of the perinea of both males and females, but were not motivated to display images of subordinate males or control stimuli. These findings endorse the view that both male and female rhesus macaques—and presumably other highly social primates—seek information about other individuals in a way that matches the adaptive value of that information for guiding social behavior.     

Long-tailed macaques (Macaca fascicularis) understand what conspecifics can see in a competitive situation

Visual perspective taking (VPT), an understanding of what others can see, is a prerequisite for theory of mind (ToM). While VPT in apes is proven, its presence in monkeys is much-debated. Several different paradigms have been developed to test its existence, but all face interpretational problems since results can be explained by simpler cognitive mechanisms than VPT. Therefore, we adjusted one method where two individuals compete for access to food, visible or invisible for the dominant competitor, to preclude cognitively simpler mechanisms. The subordinate long-tailed macaques tested, selected significantly more often the food item invisible than the item visible to the dominant. In most trials, subjects retrieved only one food item and preferred the invisible food item. Surprisingly, they occasionally adopted an alternative strategy to obtain both food items, by first choosing the visible, most at risk food item. Faster animals adopted this strategy proportionally more often than slower ones. Contrary to previous research, our results cannot be explained by simpler cognitive mechanisms, since behavioural reading was prevented by a one-way mirror between the competitor and the food, and accessibility was equal to both food items. This is the first unequivocal evidence of VPT in a monkey species, suggesting that this precursor to ToM is an evolutionarily conserved capacity present in monkeys, apes and humans.     

The smart gut: Tracking affective associative learning with measures of “liking”, facial electromyography, and preferential looking

We demonstrate here that initially neutral items can acquire specific value based on their associated outcomes, and that responses of physiological systems to such previously meaningless stimuli can rapidly reflect this associative history. Each participant participated in an associative learning task in which four neutral abstract pictures were each repeatedly paired with one of four foods that varied in valence and magnitude. Over the course of learning, participants’ “liking” ratings of and preferences for each picture came to reflect the value of the food with which it was paired. The abstract pictures also elicited physiological responses characteristic of the foods with which they were paired, including changes in facial electromyography (EMG) and preferential looking. A logistic modeling procedure showed that learning parameters, such as the rate at which participants learned the values associated with the pictures, were similar across food outcomes of different value.     

A modified mark test for own-body recognition in pig-tailed macaques (Macaca nemestrina)

Classic mirror self-recognition mark tests involve familiarizing the subject with its mirror image, surreptitiously applying a mark on the subject’s eyebrow, nose, or ear, and measuring self-directed behaviors toward the mark. For many non-human primate species, however, direct gaze at the face constitutes an aggressive and threatening signal. It is therefore possible that monkeys fail the mark test because they do not closely inspect their faces in a mirror and hence they have no expectations about their physical appearance. In the current study, we prevented two pig-tailed macaques (Macaca nemestrina) from seeing their own faces in a mirror, and we adopted a modified version of the classic mark test in which monkeys were marked on the chest, a body region to which they normally have direct visual access but that in the current study was visible only via a mirror. Neither monkey tried to touch the mark on its chest, possibly due to a failure to understand the mirror as a reflective surface. To further the monkeys’ understanding of the mirror image, we trained them to reach for food using the mirror as the only source of information. After both monkeys had learned mirror-mediated reaching, we replicated the mark test. In this latter phase of the study, only one monkey scratched the red dye on the chest once. The results are consistent with other findings suggesting that monkeys are not capable of passing a mark test and imply that face and body recognition rely on the same cognitive abilities.     

Squirrel monkeys (Saimiri sciureus) choose smaller food arrays: long-term retention, choice with nonpreferred food, and transposition

Squirrel monkeys (Saimiri sciureus) that had learned to reach toward 1 piece of food instead of 4 in a reverse-reward contingency were tested after an 8-month delay with no intervening relevant experiences. All monkeys except 1 continued to show inhibitory control by reliably reaching toward the smaller quantity, most of them doing so within 2 sessions. Performance was maintained when a low-preference food replaced prized foods as arrays and rewards. When the quantities 1 and 4 were replaced with different ones, there was strong evidence of transposition at group level, although individual differences in bias toward the smaller quantities became apparent. Individual differences in mastering the original task more than 8 months previously were quite stable, suggesting robustness in the operations required for this form of self-control.     

Social and nonsocial behaviors of adult rhesus monkeys after amygdalectomy in infancy or adulthood.

At 6 yr of age six female rhesus monkeys that had sustained bilateral amygdalectomy in infancy, and five intact controls, were transferred to an observation cage where behaviors were recorded while the monkeys were (a) alone, (b) paired with unfamiliar stimulus animals, and (c) paired with familiar monkeys from the opposite experimental group. The five adult controls then underwent amygdalectomy, and all tests were repeated with the infant- and adult-operated animals. Infant-operated monkeys changed behaviors more rapidly than did intact controls in social and nonsocial situations, and their activity levels were less modified after a 24-hr period in the observation cage. They were subordinate to intact controls but expressed less fear than did controls when briefly placed with an unfamiliar aggressive animal. Adult amygdalectomy produced many changes in behavior, but these aberrations were identical to those observed in like-age monkeys that had been amygdalectomized in infancy. Infant-operated monkeys demonstrated more behavioral deficits at 6 yr than they had earlier in life.     

Social touch alters newborn monkey behavior

In humans, infants respond positively to slow, gentle stroking—processed by C-tactile (CT) nerve fibers—by showing reductions in stress and increases in eye contact, smiling, and positive vocalizations. More frequent maternal touch is linked to greater activity and connectivity strength in social brain regions, and increases children’s attention to and learning of faces. It has been theorized that touch may prime children for social interactions and set them on a path towards healthy social cognitive development. However, less is known about the effects of touch on young infants’ psychological development, especially in the newborn period, a highly sensitive period of transition with rapid growth in sensory and social processing. It remains untested whether newborns can distinguish CT-targeted touch from other types of touch, or whether there are benefits of touch for newborns’ social, emotional, or cognitive development. In the present study, we experimentally investigated the acute effects of touch in newborn monkeys, a common model for human social development. Rhesus macaques (Macaca mulatta), like humans, are highly social, have complex mother-infant interactions with frequent body contact for the first weeks of life, making them an excellent model of infant sociality. Infant monkeys in the present study were reared in a neonatal nursery, enabling control over their early environment, including all caregiver interactions. One-week-old macaque infants (N = 27) participated in three 5-minute counter-balanced caregiver interactions, all with mutual gaze: stroking head and shoulders (CT-targeted touch), stroking palms of hands and soles of feet (Non-CT touch), or no stroking (No-touch). Immediately following the interaction, infants watched social and nonsocial videos and picture arrays including faces and objects, while we tracked their visual attention with remote eye tracking. We found that, during the caregiver interactions, infants behaved differently while being touched compared to the no-touch condition, irrespective of the body part touched. Most notably, in both touch conditions, infants exhibited fewer stress-related behaviors—self-scratching, locomotion, and contact time with a comfort object—compared to when they were not touched. Following CT-targeted touch, infants were faster to orient to the picture arrays compared to the other interaction conditions, suggesting CT-targeted touch may activate or prime infants’ attentional orienting system. In the No-touch condition infants attended longer to the nonsocial compared to the social video, possibly reflecting a baseline preference for nonsocial stimuli. In contrast, in both touch conditions, infants’ looked equally to the social and nonsocial videos, suggesting that touch may influence the types of visual stimuli that hold infants’ attention. Collectively, our results reveal that newborn macaques responded positively to touch, and touch appeared to influence some aspects of their subsequent attention, although we found limited evidence that these effects are mediated by CT fibers. These findings suggest that newborn touch may broadly support infants’ psychological development, and may have early evolutionary roots, shared across primates. This study illustrates the unique insight offered by nonhuman primates for exploring early infant social touch, revealing that touch may positively affect emotional and attentional development as early as the newborn period.     

Seeing the mind behind the art. People can distinguish abstract expressionist paintings from highly similar paintings by children, chimps, monkeys, and elephants

Museumgoers often scoff that costly abstract expressionist paintings could have been made by a child and have mistaken paintings by chimpanzees for professional art. To test whether people really conflate paintings by professionals with paintings by children and animals, we showed art and nonart students paired images, one by an abstract expressionist and one by a child or animal, and asked which they liked more and which they judged as better. The first set of pairs was presented without labels; the second set had labels (e.g., "artist," "child") that were either correct or reversed. Participants preferred professional paintings and judged them as better than the nonprofessional paintings even when the labels were reversed. Art students preferred professional works more often than did nonart students, but the two groups' judgments did not differ. Participants in both groups were more likely to justify their selections of professional than of nonprofessional works in terms of artists' intentions. The world of abstract art is more accessible than people realize.     

Further evaluation of leisure items in the attention condition of functional analyses

Research suggests that including leisure items in the attention condition of a functional analysis may produce engagement that masks sensitivity to attention. In this study, 4 individuals' initial functional analyses indicated that behavior was maintained by nonsocial variables (n = 3) or by attention (n = 1). A preference assessment was used to identify items for subsequent functional analyses. Four conditions were compared, attention with and without leisure items and control with and without leisure items. Following this, either high- or low-preference items were included in the attention condition. Problem behavior was more probable during the attention condition when no leisure items or low-preference items were included, and lower levels of problem behavior were observed during the attention condition when high-preference leisure items were included. These findings suggest how preferred items may hinder detection of behavioral function.     

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.