Research on the psychological and physiological well-being of captive animals has focused on investigating different types of social and structural enrichment. Consequently, cognitive enrichment has been understudied, despite the promising external validity, comparability, and applicability. As we aim to fill this gap, we developed an interactive, multiple-choice interface for cage-mounted touchscreen devices that rhesus monkeys (Macaca mulatta) can freely interact with, from within their home enclosure at the Cognitive Neuroscience Laboratory of the German Primate Center. The multiple-choice interface offers interchangeable activities that animals can choose and switch between. We found that all 16 captive rhesus macaques tested consistently engaged with the multiple-choice interface across 6 weekly sessions, with 11 of them exhibiting clear task preferences, and displaying proficiency in performing the selected tasks. Our approach does not require social separation or dietary restriction and is intended to increase animals’ sense of competence and agency by providing them with more control over their environment. Thanks to the high level of automation, our multiple-choice interface can be easily incorporated as a standard cognitive enrichment practice across different facilities and institutes working with captive animals, particularly non-human primates. We believe that the multiple-choice interface is a sustainable, scalable, and pragmatic protocol for enhancing cognitive well-being and animal welfare in captivity.

Limiting opportunities for captive nonhuman primates (NHPs) to express species‐specific social behaviors may disrupt the adaptive drive for social companionship and may lead to increases in coping behaviors and inactivity. While captive NHPs show improved welfare when moving to pair‐housing from single‐housing, the impact of daily separation of pair‐mates, as is implemented in intermittent pair‐housing, is not fully understood. We compared behavioral indices of welfare exhibited by adult female rhesus macaques (Macaca mulatta) in two conditions: (1) intermittent pair‐housing, involving daily overnight separation of pair‐mates, and (2) continuous pair‐housing, involving little separation of pair‐mates. A within‐subjects study design tested two groups of females experiencing both pairing conditions in an alternate order, switching either from continuous to intermittent pair‐housing, or from intermittent to continuous pair‐housing. Behavioral observations, recording activity state, self‐directed, abnormal, and social behaviors, were conducted at midday when all females were paired, and in the afternoon when intermittent pairs were separated. Females exhibited higher levels of inactivity and self‐directed behavior when separated due to intermittent pair‐housing in comparison to continuous pair‐housing. In addition, intermittently paired females showed higher levels of grooming and other types of affiliation when paired, than during the same time frame when they were continuously paired. These results suggest that females in the continuous presence of a social partner experience improved levels of activity and do not need to elevate levels of behavioral coping mechanisms (e.g., self‐scratching, increased affiliation) as they receive the benefits associated with social companionship consistently throughout the day. Overall, this study provides the first evidence that continuous pair‐housing affords better welfare than intermittent pair‐housing in adult female rhesus macaques. Pair‐housing options, such as continuous pairing, that reduce reliance on behavioral coping mechanisms and promote adaptive social behavior throughout the entirety of the day should be prioritized over husbandry care scheduled for convenience.

Understanding the impact routine research and laboratory procedures have on animals is crucial to improving their well-being and to the success and reproducibility of the research they are involved in. Cognitive measures of welfare offer insight into animals’ internal psychological state, but require validation. Attention bias – the tendency to attend to one type of information over another – is a cognitive phenomenon documented in humans and animals that is known to be modulated by affective state (i.e., emotions). Hence, changes in attention bias may offer researchers a deeper perspective of their animals’ psychological well-being. The dot-probe task is an established method for quantifying attention bias in humans (by measuring reaction time to a dot-probe replacing pairs of stimuli), but has yet to be validated in animals. We developed a dot-probe task for long-tailed macaques (Macaca fascicularis) to determine if the task can detect changes in attention bias following anesthesia, a context known to modulate attention and trigger physiological arousal in macaques. Our task included the following features: stimulus pairs of threatening and neutral facial expressions of conspecifics and their scrambled counterparts, two stimuli durations (100 and 1,000 ms), and counterbalancing of the dot-probe’s position on the touchscreen (left and right) and location relative to the threatening stimulus. We tested 8 group-housed adult females on different days relative to being anesthetized (baseline and 1-, 3-, 7-, and 14-days after). At baseline, monkeys were vigilant to threatening content when stimulus pairs were presented for 100 ms, but not 1,000 ms. On the day immediately following anesthesia, we found evidence that attention bias changed to an avoidance of threatening content. Attention bias returned to threat vigilance by the third day postanesthesia and remained so up to the last day of testing (14-days after anesthesia). We also found that attention bias was independent of the type of stimuli pair (i.e., whole face vs. scrambled counterparts), suggesting that the scrambled stimuli retained aspects of the original stimuli. Nevertheless, whole faces were more salient to the monkeys as responses to these trials were generally slower than to scrambled stimulus pairs. Overall, our study suggests it is feasible to detect changes in attention bias following anesthesia using the dot-probe task in nonhuman primates. Our results also reveal important aspects of stimulus preparation and experimental design.

Nonhuman primates (NHPs) are widely studied across many scientific disciplines using a variety of techniques in diverse environments. Due to the wide scope of NHP research, substantial overlap in research topics and questions can occur, whose resulting scientific evidence is synthesized by literature reviews. Identifying all relevant research on a particular topic involving NHPs can be difficult and time consuming. By adopting objective search development techniques from systematic reviews, we developed search filters to detect all scientific publications involving NHPs in PubMed, PsycINFO (via EBSCOhost), and Web of Science. We compared the performance of our comprehensive NHP search filters to search strings typical of a novice database user (i.e., NHP simple search strings) and validated their sensitivity by combining these searches with a topic search of cortisol related studies. For all comparisons, our comprehensive NHP search filters retrieved considerably more scientific publications than the NHP simple search strings. Importantly, our comprehensive NHP search filters are easy to use (text can be copied and pasted into the database search engine) and detect the most recent publications that have yet to be indexed by the bibliographic databases queried. Additionally, we developed filterNHP, an R package and web‐based application (https://filterNHP.dpz.eu), for researchers interested in literature searches involving a taxonomic sub‐group of NHPs. filterNHP alleviates time necessary for adapting our comprehensive NHP search filters for a particular NHP sub‐group by automatizing the creation of these search filters. Altogether, our comprehensive NHP search filters and those for taxonomic sub‐groups generated by filterNHP will enable swift and easy retrieval of the available scientific literature involving NHPs, and thereby help enhance the quality of new NHP literature reviews that guide future scientific research (new experiments) and public policy (e.g., on welfare and conservation).

Preference tests help to determine how highly individuals value different options to choose from. During preference testing, two or more options are presented simultaneously, and options are ranked based on the choices made. Presented options, however, influence each other, where the amount of influence increases with the number of options. Multiple binary choice tests can reduce this degree of influence, but conventional analysis methods do not reveal the relative strengths of preference, i.e., the preference difference between options. Here, we demonstrate that multiple binary comparisons can be used not only to rank but also to scale preferences among many options (i.e., their worth value). We analyzed human image preference data with known valence scores to develop and validate our approach to determine how known valence ranges (high vs. low) converge on a scaled representation of preference data. Our approach allowed us to assess the valence of ranked options in mice and rhesus macaques. By conducting simulations, we developed an approach to incorporate additional option choices into existing rank orders without the need to conduct binary choice tests with all original options, thus reducing the number of animal experiments needed. Two quality measures, consensus error and intransitivity ratio, allow for assessing the achieved confidence of the scaled ranking and better tailoring of measurements required to improve it further. The software is available as an R package (“simsalRbim”). Our approach optimizes preference testing, e.g., in welfare assessment, and allows us to efficiently and quantitatively assess the relative value of options presented to animals.

One primary goal of laboratory animal welfare science is to provide a comprehensive severity assessment of the experimental and husbandry procedures or conditions these animals experience. The severity, or degree of suffering, of these conditions experienced by animals are typically scored based on anthropocentric assumptions. We propose to (a) assess an animal’s subjective experience of condition severity, and (b) not only rank but scale different conditions in relation to one another using choice-based preference testing. The Choice-based Severity Scale (CSS) utilizes animals’ relative preferences for different conditions, which are compared by how much reward is needed to outweigh the perceived severity of a given condition. Thus, this animal-centric approach provides a common scale for condition severity based on the animal’s perspective. To assess and test the CSS concept, we offered three opportunistically selected male rhesus macaques (Macaca mulatta) choices between two conditions: performing a cognitive task in a typical neuroscience laboratory setup (laboratory condition) versus the monkey’s home environment (cage condition). Our data show a shift in one individual’s preference for the cage condition to the laboratory condition when we changed the type of reward provided in the task. Two additional monkeys strongly preferred the cage condition over the laboratory condition, irrespective of reward amount and type. We tested the CSS concept further by showing that monkeys’ choices between tasks varying in trial duration can be influenced by the amount of reward provided. Altogether, the CSS concept is built upon laboratory animals’ subjective experiences and has the potential to de-anthropomorphize severity assessments, refine experimental protocols, and provide a common framework to assess animal welfare across different domains.