Humans show a global advantage when processing hierarchical visual patterns, and they detect the global level of stimulus structure more accurately and faster than the local level in several stimulus contexts. By contrast, capuchins (Cebus apella) and other monkey species show a strong local advantage. A key factor which, if manipulated, could cause an inversion of this effect in monkeys is still to be found. In this study, we examined whether it was possible to induce attention allocation to global and local levels of perceptual analysis in capuchin monkeys and if by doing so, their local dominance could be reversed. We manipulated attentional bias using a matching-to-sample (MTS) task where the proportion of trials requiring global and local processing varied between conditions. The monkeys were compared with humans tested with the same paradigm. Monkeys showed a local advantage in the local bias condition but a global advantage in the global bias condition. The role of attention in processing was confined to the local trials in a first phase of testing but extended to both local and global trials in the course of task practice. Humans exhibited an overall global dominance and an effect of attentional bias on the speed of processing of the global and local level of the stimuli. These results indicate a role for attention in the processing of hierarchical stimuli in monkeys and are discussed in relation to the extent to which they can explain the differences between capuchin monkeys and humans observed in this and other studies.

Urine washing is a common behavior in strepsirrhine and platyrrhine primates, but its function is still poorly understood. We investigated the factors influencing urine washing behavior in 2 captive groups of tufted capuchins (Cebus apella). Urine washing was affected by group membership (subjects in the 2 groups urine washed at different rates) and was negatively related to age, but was not influenced by sex or dominance rank. Females urine washed less when in estrus, and the presence of an estrous female did not affect male urine washing behavior. We observed independent effects of diurnal and climatic variables on urine washing. Tufted capuchins urine washed more at midday and under conditions of higher temperatures and lower relative humidity. Both of the latter effects were evident only at the lowest temperatures (5-20°C). Our results indicate that urine washing is sensitive to multiple influences, and that hypothetical communicative or thermoregulatory functions do not fully account for its occurrence.

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