Taï chimpanzees use botanical skills to discover fruit: what we can learn from their mistakes

Fruit foragers are known to use spatial memory to relocate fruit, yet it is unclear how they manage to find fruit in the first place. In this study, we investigated whether chimpanzees (Pan troglodytes verus) in the Taï National Park make use of fruiting synchrony, the simultaneous emergence of fruit in trees of the same species, which can be used together with sensory cues, such as sight and smell, to discover fruit. We conducted observations of inspections, the visual checking of fruit availability in trees, and focused our analyses on inspections of empty trees, so to say “mistakes”. Learning from their “mistakes”, we found that chimpanzees had expectations of finding fruit days before feeding on it and significantly increased inspection activity after tasting the first fruit. Neither the duration of feeding nor density of fruit-bearing trees in the territory could account for the variation in inspection activity, which suggests chimpanzees did not simply develop a taste for specific fruit on which they had fed frequently. Instead, inspection activity was predicted by a botanical feature—the level of synchrony in fruit production of encountered trees. We conclude that chimpanzees make use of the synchronous emergence of rainforest fruits during daily foraging and base their expectations of finding fruit on a combination of botanical knowledge founded on the success rates of fruit discovery, and a categorization of fruit species. Our results provide new insights into the variety of food-finding strategies employed by primates and the adaptive value of categorization capacities.     

Is approximate numerical judgment truly modality-independent? Visual, auditory, and cross-modal comparisons

The numerosity of any set of discrete elements can be depicted by a genuinely abstract number representation, irrespective of whether they are presented in the visual or auditory modality. The accumulator model predicts that no cost should apply for comparing numerosities within and across modalities. However, in behavioral studies, some inconsistencies have been apparent in the performance of number comparisons among different modalities. In this study, we tested whether and how numerical comparisons of visual, auditory, and cross-modal presentations would differ under adequate control of stimulus presentation. We measured the Weber fractions and points of subjective equality of numerical discrimination in visual, auditory, and cross-modal conditions. The results demonstrated differences between the performances in visual and auditory conditions, such that numerical discrimination of an auditory sequence was more precise than that of a visual sequence. The performance of cross-modal trials lay between performance levels in the visual and auditory conditions. Moreover, the number of visual stimuli was overestimated as compared to that of auditory stimuli. Our findings imply that the process of approximate numerical representation is complex and involves multiple stages, including accumulation and decision processes.     

Taï chimpanzees anticipate revisiting high-valued fruit trees from further distances

The use of spatio-temporal memory has been argued to increase food-finding efficiency in rainforest primates. However, the exact content of this memory is poorly known to date. This study investigated what specific information from previous feeding visits chimpanzees (Pan troglodytes verus), in Taï National Park, Côte d’Ivoire, take into account when they revisit the same feeding trees. By following five adult females for many consecutive days, we tested from what distance the females directed their travels towards previously visited feeding trees and how previous feeding experiences and fruit tree properties influenced this distance. To exclude the influence of sensory cues, the females’ approach distance was measured from their last significant change in travel direction until the moment they entered the tree’s maximum detection field. We found that chimpanzees travelled longer distances to trees at which they had previously made food grunts and had rejected fewer fruits compared to other trees. In addition, the results suggest that the chimpanzees were able to anticipate the amount of fruit that they would find in the trees. Overall, our findings are consistent with the hypothesis that chimpanzees act upon a retrieved memory of their last feeding experiences long before they revisit feeding trees, which would indicate a daily use of long-term prospective memory. Further, the results are consistent with the possibility that positive emotional experiences help to trigger prospective memory retrieval in forest areas that are further away and have fewer cues associated with revisited feeding trees.     

Culture and egocentric perceptions of fairness in conflict and negotiation

In this article, the authors advanced a cultural view of judgment biases in conflict and negotiation. The authors predicted that disputants' self-serving biases of fairness would be more prevalent in individualistic cultures, such as the United States, in which the self is served by focusing on one's positive attributes to "stand out" and be better than others, yet would be attenuated in collectivistic cultures, such as Japan, where the self is served by focusing on one's negative characteristics to "blend in" (S. J. Heine, D. R. Lehman, H. R. Markus, & S. Kitayama, 1999). Four studies that used different methodologies (free recall, scenarios, and a laboratory experiment) supported this notion. Implications for the science and practice of negotiation are discussed.     

Biochemical pathogenesis of post-traumatic epilepsy

The online version of the original article can be found at     

Biochemical pathogenesis of post-traumatic epilepsy

Head trauma is often followed by epilepsy and may be related to the breakdown of red blood cells and hemoglobin within the CNS. Injection of hemoglobin or iron salts into the rat cortex is known to induce a chronic epileptic focus. We observed the formation of superoxide anion (O₂) and hydroxyl radical (·OH) after ferric chloride injection into the rat cerebral cortex and suggest that these radicals, especially ·OH, may be responsible for the initiation of lipid peroxidation in neuronal membranes and for the accelerated production of guanidine compounds in the brain, which may in turn lead to epileptogenicity. Then, we found that treatment with epigallocatechin (EGC) or a phosphate diester of vitamins E and C (EPC), which are potent ·OH scavengers, significantly inhibited the formation of malondialdehyde and epileptic discharges in the iron-induced epileptic focus. This study was supported by a grant-in-aid for scientific research from the Japanese Ministry of Education, Science, and Culture.