A songbird can detect the eyes of conspecifics under daylight and artificial nighttime lighting.

Eyes convey important information about the external and internal worlds of animals. Individuals can follow the gaze of others to learn about the location of salient objects as well as assess eye qualities to evaluate the health, age or other internal states of conspecifics. Because of the increasing prevalence of artificial lighting at night (ALAN), urbanized individuals can potentially garner information from conspecific eyes under both daylight and ALAN. We tested this possibility using a visual modeling approach in which we estimated the maximum distance at which individuals could detect conspecific eyes under daylight and high levels of ALAN. We also estimated the minimum light level at which individuals could detect conspecific eyes. Great-tailed grackles (Quiscalus mexicanus) were used as our study species because they are highly social and are unusual among birds in that they regularly gather at nocturnal roosts in areas with high levels of ALAN. This visual modelling approach revealed that grackles can detect conspecific eyes under both daylight and ALAN, regardless of iris coloration. The grackles could detect conspecific eyes at farther distances in daylight compared to ALAN. Our results highlight the potential importance of lighting conditions in shaping social interactions.

The gaze of a social monkey is perceptible to conspecifics and predators but not prey.

Eye gaze is an important source of information for animals, implicated in communication, cooperation, hunting and antipredator behaviour. Gaze perception and its cognitive underpinnings are much studied in primates, but the specific features that are used to estimate gaze can be difficult to isolate behaviourally. We photographed 13 laboratory-housed tufted capuchin monkeys (Sapajus [Cebus] apella) to quantify chromatic and achromatic contrasts between their iris, pupil, sclera and skin. We used colour vision models to quantify the degree to which capuchin eye gaze is discriminable to capuchins, their predators and their prey. We found that capuchins, regardless of their colour vision phenotype, as well as their predators, were capable of effectively discriminating capuchin gaze across ecologically relevant distances. Their prey, in contrast, were not capable of discriminating capuchin gaze, even under relatively ideal conditions. These results suggest that specific features of primate eyes can influence gaze perception, both within and across species.

Chimpanzee (Pan troglodytes) gaze is conspicuous at ecologically-relevant distances.

Chimpanzee (Pan troglodytes) sclera appear much darker than the white sclera of human eyes, to such a degree that the direction of chimpanzee gaze may be concealed from conspecifics. Recent debate surrounding this topic has produced mixed results, with some evidence suggesting that (1) primate gaze is indeed concealed from their conspecifics, and (2) gaze colouration is among the suite of traits that distinguish uniquely social and cooperative humans from other primates (the cooperative eye hypothesis). Using a visual modelling approach that properly accounts for specific-specific vision, we reexamined this topic to estimate the extent to which chimpanzee eye coloration is discriminable. We photographed the faces of captive chimpanzees and quantified the discriminability of their pupil, iris, sclera, and surrounding skin. We considered biases of cameras, lighting conditions, and commercial photography software along with primate visual acuity, colour sensitivity, and discrimination ability. Our visual modeling of chimpanzee eye coloration suggests that chimpanzee gaze is visible to conspecifics at a range of distances (within approximately 10 m) appropriate for many species-typical behaviours. We also found that chimpanzee gaze is discriminable to the visual system of primates that chimpanzees prey upon, Colobus monkeys. Chimpanzee sclera colour does not effectively conceal gaze, and we discuss this result with regard to the cooperative eye hypothesis, the evolution of primate eye colouration, and methodological best practices for future primate visual ecology research.

Nonhuman primates learn adjacent dependencies but fail to learn nonadjacent dependencies in a statistical learning task with a salient cue.

There is ample evidence that humans and nonhuman animals can learn complex statistical regularities presented within various types of input. However, humans outperform their nonhuman primate counterparts when it comes to recognizing relationships that exist across one or several intervening stimuli (nonadjacent dependencies). This is especially true when the two elements in the dependency do not share any perceptual similarity (arbitrary associations). In the present study, we investigated whether manipulating the saliency of the predictive stimulus would enhance nonadjacent dependency learning in nonhuman primates. Rhesus macaques and tufted capuchins engaged in a computerized signal detection task that included sequences that were random in nature, included an adjacent dependency, or included a nonadjacent dependency. We manipulated the saliency of the predictive stimulus, such that the predictor jittered in place on the screen in some grammar blocks, as well as the transitional probability (the likelihood of the stimulus preceding the target to accurately predict the target's appearance) from block to block. Some monkeys evidenced learning of adjacent dependencies by faster response times to targets that followed a predictive stimulus compared to targets that were not preceded by a predictor. However, consistent with the body of evidence that indicates that nonhuman animals' statistical learning mechanisms are not at the same level of sophistication as humans', there was no evidence that monkeys learned nonadjacent dependencies of arbitrary associations, even when the salient cue was present.

Strategy use in probabilistic categorization by rhesus macaques (Macaca mulatta) and capuchin monkeys (Cebus [Sapajus] apella).

Probabilistic categorization tasks present the learner with a set of possible responses and imperfect cue evidence of which response will be rewarded. A single, optimal integration of all available cues into an optimal response is possible given any set of evidence. In contrast, there are many possible uses of the cues that offer the learner suboptimal (but better than chance) responding. We presented a classic probabilistic categorization task to 3 rhesus macaques (Macaca mulatta) and 13 capuchin monkeys (Cebus [Sapajus] apella) to explore what strategies for integration of imperfectly predictive stimulus information would be used by the animals. Using the strategy analysis models that have been previously used to describe human strategy use in probabilistic categorization tasks, we fit each of thousands of blocks of responses to 25 types of response strategies ranging from complex cognitive strategies (e.g., optimal integration of all evidence) to heuristic strategies (e.g., identify a highly predictive cue and respond based only on its presence or absence) to rote behavior (e.g., choosing the same response every trial). Inferences about strategy use were highly stable within animals and were heterogeneous across animals, with some animals never using cue information and others using it fruitfully. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Post-event misinformation effects in a language-trained chimpanzee (Pan troglodytes).

Errors of source monitoring are widespread human memory challenges, and our memories are subject to distortion upon the presentation of subsequent misinformation. Less is known about if and when misinformation effects occur in nonhuman species' memory. Here we tested a symbol-trained chimpanzee's recall memory of a hidden food item's identity after a 10-min delay. During this delay, the subject was sometimes (depending on the condition) shown consistent or inconsistent video information about the identity of the food, before being asked to name the item to a second experimenter blind to the reward and condition. Across all conditions, our subject, Sherman, correctly named the food item at above chance levels. In the Inconsistent condition, in which Sherman was shown a video with misleading information, his performance was the worst of all conditions (although accuracy was still high). Interestingly, however, during three of the four trials in this condition in which Sherman made a mistake, he incorrectly named the food item shown during the misleading video information. These results provide evidence that chimpanzees, like humans, may be vulnerable to misinformation effects, even when that misleading information is presented in a different modality (video) than the original live event memory, demonstrating further commonality between human and ape memory systems.

Divide and Conquer.

We assessed the ability of preschool children to assign the most difficult tasks to a symbolic helper. First, children were taught that a toy "helper" could aid them in remembering the location of a hidden item. Children preferentially assigned the helper to the objectively most difficult locations to remember. Each child then completed eight more tests, assessing a range of different skills such as counting, object identification, and word reading. Children again could assign some stimuli in each task to the helper, leaving the remaining stimuli for themselves to respond to in the given tasks. They were not explicitly told to assign the hardest stimulus to the helper. However, children consistently still did so in most tasks, although some tasks showed an effect of age where older children were more proficient in assigning the objectively more difficult stimuli to the helper. These results highlight a potential form of metacognition in young children in which they can monitor difficulty across varied kinds of assessments and use a generalized tool for asking for help that does not require verbal responding.

Chimpanzees can point to smaller amounts of food to accumulate larger amounts but they still fail the reverse-reward contingency task.

The reverse-reward contingency task presents 2 food sets to an animal, and they are required to choose the smaller of the 2 sets in order to receive the larger food set. Intriguingly, the majority of species tested on the reverse-reward task fail to learn this contingency in the absence of large trial counts, correction trials, and punishment techniques. The unique difficulty of this seemingly simple task likely reflects a failure of inhibitory control which is required to point toward a smaller and less desirable reward rather than a larger and more desirable reward. This failure by chimpanzees and other primates to pass the reverse-reward task is striking given the self-control they exhibit in a variety of other paradigms. For example, chimpanzees have consistently demonstrated a high capacity for delay of gratification in order to maximize accumulating food rewards in which foods are added item-by-item to a growing set until the subject consumes the rewards. To study the mechanisms underlying success in the accumulation task and failure in the reverse-reward task, we presented chimpanzees with several combinations of these 2 tasks to determine when chimpanzees might succeed in pointing to smaller food sets over larger food sets and how the nature of the task might determine the animals' success or failure. Across experiments, 3 chimpanzees repeatedly failed to solve the reverse-reward task, whereas they accumulated nearly all food items across all instances of the accumulation self-control task, even when they had to point to small amounts of food to accumulate larger amounts. These data indicate that constraints of these 2 related but still different tasks of behavioral inhibition are dependent upon the animals' perceptions of the choice set, their sense of control over the contents of choice sets, and the nature of the task constraints. (PsycINFO Database Record

Self-control assessments of capuchin monkeys with the rotating tray task and the accumulation task.

Recent studies of delay of gratification in capuchin monkeys using a rotating tray (RT) task have shown improved self-control performance in these animals in comparison to the accumulation (AC) task. In this study, we investigated whether this improvement resulted from the difference in methods between the rotating tray task and previous tests, or whether it was the result of greater overall experience with delay of gratification tasks. Experiment 1 produced similar performance levels by capuchins monkeys in the RT and AC tasks when identical reward and temporal parameters were used. Experiment 2 demonstrated a similar result using reward amounts that were more similar to previous AC experiments with these monkeys. In Experiment 3, monkeys performed multiple versions of the AC task with varied reward and temporal parameters. Their self-control behavior was found to be dependent on the overall delay to reward consumption, rather than the overall reward amount ultimately consumed. These findings indicate that these capuchin monkeys' self-control capacities were more likely to have improved across studies because of the greater experience they had with delay of gratification tasks. Experiment 4 and Experiment 5 tested new, task-naïve monkeys on both tasks, finding more limited evidence of self-control, and no evidence that one task was more beneficial than the other in promoting self-control. The results of this study suggest that future testing of this kind should focus on temporal parameters and reward magnitude parameters to establish accurate measures of delay of gratification capacity and development in this species and perhaps others.