The Producer–Scrounger game proposes that individuals in social foraging situations tend to choose one of two strategies: (a) actively invest effort in searching for resources (producing) or (b) exploit resources discovered by others (scrounging). Models have typically given scroungers an advantage. In Vickery et al.’s (1991) model, remaining food in a patch is equally shared among scroungers regardless of their position or visual range. Similarly, agent-based models assume scroungers have a comprehensive view of the habitat, enabling them to detect all opportunities to exploit resources, while producers move randomly. This study examined the effect of visual range on producer–scrounger dynamics using a computerized behavioral task where four human participants interacted in real time within a virtual habitat. Two groups, differing in food probability (λ80 and λ20), were exposed to four experimental conditions that varied visual range by manipulating the top-down camera angle (45° or 75°) and camera distance (240 or 80 px). Results showed that the producer index was higher when the probability of finding resources increased, and highest in the 75°–240 px condition, where participants had limited depth of view but could better perceive their immediate surroundings. A modified agent-based model that included visual range parameters revealed a similar pattern. These findings highlight the importance of visual range, often underestimated in theoretical models, for producer strategies.

Cotton-top tamarins (n = 14, aged 7–24 years) were tested over a 10-year period on tasks conventionally differentiating aging from dementia in humans. Three tasks were developed on iPads to collect response accuracies in tests of attention (visual search [VS]), working memory (delayed matching-to-sample), and executive processing (rule-shifting). A fourth task utilized a spontaneous object recognition paradigm to test familiarity memory in the subjects’ home cages. Linear regression analyses revealed cognitive decline with increasing age in particular components of these tasks. Specifically, accuracy to direct attention in a VS to targets with overlapping features decreased with age. All older monkeys showed accuracy to remember sample items through 1- and 10-s delays in a recognition test, but their ability to remember through these delays was compromised with more extreme aging. Rule-shifting involving attending to a dimension previously irrelevant to the game was particularly problematic with increased age. Cognitive maintenance with aging occurred with simpler VS targets, rule-shifting within the same dimension or feature, and familiarity memory. Tamarins’ initiation of cognitive decline mapped closely to the age found in published work of the accumulation of Aβ (beta amyloid species and plaques) in tamarins. The failures in cognition in aging tamarins corresponded with common failures in elderly humans. Moreover, eight of the 14 tamarins showed more severe cognitive deterioration that might signal a kind of dementia. Further study is needed to measure cognitive maintenance and loss across a variety of species of primates with different lifespans and backgrounds.

Like other domesticated species, most notably dogs, horses have been reported to follow human gestures and successfully use them to gain rewards in an object choice task. Empirical support for the hypothesis that a domain-general mechanism may underlie this ability comes from studies in which horses have successfully solved the task by using not just a human pointing gesture but also an arbitrary physical cue, namely a wooden marker. Here, we replicated the two conditions in which these two cues were used by Proops et al. (2010) with two critical changes: first, we positioned the marker out of the horses’ sight, and second, we positioned the marker such that it was in the same position where the gesture would be when the experimenter showed the pointing gesture. Horses successfully solved the task using both the pointing gesture and the marker, and their performance did not differ statistically significantly between these two conditions. The robustness of this result was corroborated by complementary model comparisons, which further showed that the horses’ performance was not significantly influenced by their age or sex. Our findings thus support the consistency of previously reported findings in these specific testing conditions and suggest that at least part of the horses’ ability to solve the object choice task with different types of cues is based on a domain-general mechanism.

The matching law, which posits that animals allocate their responses in proportion to the rate of reinforcement, has been supported across diverse animal taxa. Although originally formulated in the context of operant choice, matching also applies to time allocation in foraging and to Pavlovian responses, indicating its generality across behavioral domains. However, empirical evidence has thus far been largely limited to vertebrates and arthropods. Addressing the broader applicability of this principle requires extending investigations beyond these taxonomic groups, across a wider phylogenetic spectrum. Here, we examined phototactic behavior in the acoel flatworm Praesagittifera naikaiensis, a species that acquires nutrients through photosynthesis by symbiotic algae and exhibits positive phototaxis. Using a custom-built T-maze in which the number of illuminated LEDs varied across arms, we found that the animals distributed themselves in proportion to relative brightness, consistent with matching behavior. Moreover, prior exposure to light for 24 hr attenuated this pattern. This manipulation was intended to induce a state of nutritional sufficiency, and the resulting decline in phototactic responses suggests that internal physiological states can modulate even seemingly reflexive locomotor behaviors.

The use of plants with medicinal properties by nonhuman animals has been extensively documented. However, little emphasis has been placed on evidence suggesting that animals also appear to use/consume substances with psychoactive properties. This psychological self-medication (PsycSM) hypothesis posits that the voluntary use of substances that alter emotional/mental states is guided by the substance’s ability to reduce negative states or promote positive states. The objective of this narrative review is to provide a rigorous interpretation and critique of findings, point out contributions and limitations of available research, and provide a synthesis useful to design further studies aimed at testing the PsycSM hypothesis. Criteria derived from this hypothesis are used to establish behaviors as PsycSM examples. Areas for potentially useful interactions between field and laboratory research are specified. Anecdotal evidence from field observations suggests that animals voluntarily consume substances that affect their emotional state. Although laboratory research reviewed herein suggests that nonhuman animals intentionally consume substances that can affect their emotional/mental state, the underlying mechanisms are still poorly understood. One such mechanism is hypothesized to involve a reinforcement process produced by a change in the internal state contingent on substance consumption, whether to reduce negative emotions or to enhance positive emotions. The criteria for PsycSM developed in this review may guide further research into these effects.