Hidden Food Reward Research Articles

Intuitive optics: what great apes infer from mirrors and shadows

There is ongoing debate about the extent to which nonhuman animals, like humans, can go beyond first-order perceptual information to abstract structural information from their environment. To provide more empirical evidence regarding this question, we examined what type of information great apes (chimpanzees, bonobos, and orangutans) gain from optical effects such as shadows and mirror images. In an initial experiment, we investigated whether apes would use mirror images and shadows to locate hidden food. We found that all examined ape species used these cues to find the food. Follow-up experiments showed that apes neither confused these optical effects with the food rewards nor did they merely associate cues with food. First, naïve chimpanzees used the shadow of the hidden food to locate it but they did not learn within the same number of trials to use a perceptually similar rubber patch as indicator of the hidden food reward. Second, apes made use of the mirror images to estimate the distance of the hidden food from their own body. Depending on the distance, apes either pointed into the direction of the food or tried to access the hidden food directly. Third, apes showed some sensitivity to the geometrical relation between mirror orientation and mirrored objects when searching hidden food. Fourth, apes tended to interpret mirror images and pictures of these mirror images differently depending on their prior knowledge. Together, these findings suggest that apes are sensitive to the optical relation between mirror images and shadows and their physical referents.

Experience with featural-cue reliability influences featural- and geometric-cue use by mice (Mus musculus).

Orienting is a critical skill for all mobile animals. Two commonly studied visual components used to guide orientation in an environment are geometric (e.g., distance or direction) and featural cues (e.g., color or texture). Previous research has shown that visual-cue use and cue weighing can depend on the navigator's previous experience, the nature and reliability of the cues, and genetic factors. Accordingly, the domestic mouse (Mus musculus) is a species of increasing interest because of its potential as a model for human neurological disorders with associated spatial disorientation, as is seen in Alzheimer's disease. In the present study, adult C57BL/6 mice were trained to search for a hidden food reward in one corner of a rectangular environment with featural information displayed continuously along the walls. After training, one group of mice was given a block of testing in which the featural information was removed, followed by a second block of testing in which the featural information was put in conflict with the learned configuration of featural and geometric cues. A second group of mice was given the same set of tests, but in the reverse order. Our results show that the mice incidentally encoded the geometry of the environment if they had experience with featural cues being unreliable prior to tests, during which featural cues were completely removed (unstable). Furthermore, we found when featural and geometric cues provide conflicting spatial information, this unreliability of featural cues over the course of the study may influence cue weighing. (PsycINFO Database Record

Pre-weaning dietary iron deficiency impairs spatial learning and memory in the cognitive holeboard task in piglets.

Iron deficiency is the most common nutritional deficiency in humans, affecting more than two billion people worldwide. Early-life iron deficiency can lead to irreversible deficits in learning and memory. The pig represents a promising model animal for studying such deficits, because of its similarities to humans during early development. We investigated the effects of pre-weaning dietary iron deficiency in piglets on growth, blood parameters, cognitive performance, and brain histology later in life. Four to six days after birth, 10 male sibling pairs of piglets were taken from 10 different sows. One piglet of each pair was given a 200 mg iron dextran injection and fed a control milk diet for 28 days (88 mg Fe/kg), whereas the other sibling was given a saline injection and fed an iron deficient (ID) milk diet (21 mg Fe/kg). Due to severely retarded growth of two of the ID piglets, only eight ID piglets were tested behaviorally. After dietary treatment, all piglets were fed a balanced commercial pig diet (190–240 mg Fe/kg). Starting at 7.5 weeks of age, piglets were tested in a spatial cognitive holeboard task. In this task, 4 of 16 holes contain a hidden food reward, allowing measurement of working (short-term) memory and reference (long-term) memory (RM) simultaneously. All piglets received 40–60 acquisition trials, followed by a 16-trial reversal phase. ID piglets showed permanently retarded growth and a strong decrease in blood iron parameters during dietary treatment. After treatment, ID piglets' blood iron values restored to normal levels. In the holeboard task, ID piglets showed impaired RM learning during acquisition and reversal. Iron staining at necropsy at 12 weeks of age showed that ID piglets had fewer iron-containing cells in hippocampal regions CA1 and dentate gyrus (DG). The number of iron-containing cells in CA3 correlated positively with the average RM score during acquisition across all animals. Our results support the hypothesis that early-life iron deficiency leads to lasting cognitive deficits. The piglet as a model animal, tested in the holeboard, can be useful in future research for assessing long-term cognitive effects of early-life diets or diet-induced deficiencies.

How Clark's nutcrackers (Nucifraga columbiana) weigh geometric cues depends on their previous experience.

Following passive disorientation, Clark's nutcrackers (Nucifraga columbiana) learned to search for a hidden food reward located in one corner of a rectangular-shaped enclosure that contained either identical or distinct features in each corner. Identical features allowed for explicit learning of geometric cues, whereas distinct features allowed for both explicit learning of featural cues and incidental learning of geometric cues. Birds that only learned about geometry incidentally (group Distinct) weighed features greater than geometry when the two cues were placed in conflict. However, birds that received explicit training with geometry, in addition to feature training (groups Distinct-Identical and Identical-Distinct), weighed geometry heavier relative to features. Cue preference by the birds also depended on the order in which learning was experienced; if explicit training with geometry followed that of features (group Distinct-Identical), then both geometry and features were weighed equally, but if explicit training with geometry training preceded that of features (group Identical-Distinct), the birds weighed geometry greater than features. Results suggest both a heightened sensitivity to geometric cues by Clark's nutcrackers relative to other species of birds and an increased sensitivity to any spatial cue (either features or geometry) that has proven both stable and reliable.

Intentional gestural communication and discrimination of human attentional states in rhesus macaques (Macaca mulatta).

The present study tested intentionality of a learned begging gesture and attention-reading abilities in rhesus macaques (Macaca mulatta). Subjects were trained to produce a begging gesture towards a hidden food reward that could be delivered by a human experimenter. More specifically, we investigated which attentional cues--body, face and/or eyes orientation of a human partner--were taken into account by the macaques in order to communicate with her. Our results provide strong evidence of intentional communication: the monkeys adjusted their behaviour to that of the partner. The latter's attentional state influenced the monkeys' likelihood of performing begging gestures and showing gaze alternation between the partner and the hidden food. By contrast, we found no evidence of attention-getting behaviours, persistence or elaboration of new communicative behaviours. Our results also showed that rhesus macaques discriminated gross cues including the presence, body and face orientation of the human experimenter but not her eyes. However, the monkeys emitted more gaze alternation and monitored the human's attentional state more closely when she also displayed gaze alternation, suggesting an important role of joint attention in gestural communication.

Very low birth weight piglets show improved cognitive performance in the spatial cognitive holeboard task.

Low birth weight (LBW) is common in humans and has been found to cause lasting cognitive and developmental deficits later in life. It is thought that the primary cause is intra-uterine growth restriction (IUGR) due to a shortage of oxygen and supply of nutrients to the fetus. Pigs appear to be a good model animal to investigate long-term cognitive effects of LBW, as LBW is common in commercially farmed breeds of pigs. Moreover, pigs are developmentally similar to humans and can be trained to perform complex tasks. In this study, we trained ten very low birth weight (vLBW) piglets and their ten normal birth weight (NBW) siblings in a spatial cognitive holeboard task in order to investigate long-term cognitive effects of LBW. In this task, four out of sixteen holes contain a hidden food reward, which allows measuring working memory (WM) (short-term memory) and reference memory (RM) (long-term memory) in parallel. Piglets were trained for 46–54 trials during the acquisition phase, followed by a 20-trial reversal phase in which a different set of four holes was baited. Both groups acquired the task and improved their performance over time. A mixed model repeated measures ANOVA revealed that vLBW piglets showed better RM performance than NBW piglets in both the acquisition and reversal phase. Additionally, WM scores in the vLBW were less disrupted than in the NBW animals when switched to the reversal phase. These findings are contrary to findings in humans. Moreover, vLBW pigs had lower hair cortisol concentrations (HCCs) than NBW pigs in flank hair at 12 weeks of age. These results could indicate that restricted intra-uterine growth causes compensatory mechanisms to arise in early development that result in beneficial effects for vLBW piglets, increasing their low survival chances in early-life competition.

Social Learning in the Caracara Chimango,Milvago chimango(Aves: Falconiformes): an Age Comparison

AbstractMilvago chimangois a gregarious raptor showing great ecological plasticity. Their ability to explore new resources has allowed them to survive in areas with increasing human modification. In this study, we evaluated the social learning ability in wild‐caught individuals ofM. chimango. In particular, we tested whether an ‘observer’ individual could improve the acquisition of a novel behaviour by watching a ‘demonstrator,’ and we examined the effects of age of both observers and demonstrators on social learning. We measured the ability of 18 observers to open an opaque Plexiglas box containing food, and we compared their performance to that of 10 control birds who did not watch a demonstrator solve the task. Prior to watching a demonstrator, only two of the observers and two of the control birds were able to open the box. After watching a demonstrator, 67% of observers were able to open the box, outperforming control birds in speed and success. Juvenile observers were more successful and faster than adults at contacting and opening the box. The age of the demonstrator did not influence the observers’ likelihood of success. These results showed thatM. chimangoare able to learn a box‐opening task with a hidden food reward by observing the behaviour of a conspecific and that this behaviour persisted over several days. Social learning ability inM. chimangomight allow certain behavioural patterns, such as those related to novel resource acquisition in modified environments, to be socially transmitted among individuals in a population.

Physical and social cognition in domestic dogs: A comparative study

Dogs have shown outstanding social cognitive skills when interacting with humans, especially in situations where social knowledge and communicative skills are needed. On the other hand, when tested on knowledge of objects or understanding of causality, domestic dogs did not prove to be particularly skilled and flexible when compared with other species. Brauer et al. (2006) showed that chimpanzees outperformed dogs in an object choice paradigm when causal cues were provided. However, chimpanzees failed to use social information given by the experimenter, whereas domestic dogs used several social communicative cues to receive a hidden food reward. To test whether these differences in performance hold true over a larger set of cognitive tests covering both physical and social cognition, we tested 97 domestic dogs modifying the Primate Cognition Test Battery (PCTB). This extensive test battery was developed by Herrmann et al. (2007) to investigate the cognitive abilities of great apes and human children and includes tests on knowledge of objects, quantities and causal understanding (physical domain) and social cognitive tasks like social learning, communication and knowledge of others’ actions and minds (social domain). Averaging across all of the tasks in the physical domain, dogs were correct in 45% of the trials, whereas chimpanzees succeeded in 68% of the trials. In the social domain, dogs performed correctly in 34% of the trials, and chimpanzees were correct in 39% of the trials. Statistically, chimpanzees outperformed dogs in physical cognitive tasks as well as in social cognitive tasks. Comparing the particular scales, we did find statistical differences between the species for all 3 scales of physical cognition as well as for tasks requiring knowledge of others’ actions and minds. Although domestic dogs and chimpanzees performed at a similar level over all communicative and social learning tasks, we did find species differences within single tasks. Our results show that chimpanzees outperform dogs not only in causal understanding, but also in a variety of other physical cognitive skills such as knowledge of space and Cognition 49

On the rewarding nature of appetitive feeding behaviour in pigs ( Sus scrofa): Do domesticated pigs contrafreeload?

Contrafreeloading is the phenomenon that animals prefer to “work” for food even though “free” food is available nearby. In this study, we investigated whether pigs express contrafreeloading in a test situation where the searching, finding and consuming of food items resembles a natural foraging situation. For that purpose, we investigated whether pigs prefer an environment with straw and hidden food rewards (chocolate raisins) to an environment with straw, but without hidden food rewards and with food rewards “freely” available in a trough. Preference behaviour was investigated in a Conditioned Place Preference task (CPP). Typically, CPP measures the conditioned preference in the absence of reinforcers so that unwanted interference with the reinforcers during testing does not take place. The results show that (a) CPP can be used to establish the preference of pigs for different environments (experiments 1–4); (b) that pigs prefer to forage for food over “freely” available food from a trough (experiment 3) and (c) that anticipating a food reward has reinforcing effects above and beyond the reinforcing effects of acquisition of a food reward alone (experiment 4). The results therefore show that pigs express contrafreeloading when using a natural foraging task and they suggest that the reinforcing effects of anticipation, which occurs during natural foraging in the delays between searching and finding food, may contribute to the observed expression of contrafreeloading in pigs.