Diurnal primates mostly rely on sight to gather information from the environment. However, the tactile input seems to be as essential as visual input and the development of tactile memory can significantly contribute to fast object recognition. Particularly, visuo-tactile integration is supposed to be more important in the discrimination of surface features of objects compared to larger-scale features such as size and shape. The present study, conducted on capuchin monkeys (Sapajus spp.), aimed to assess (i) whether the learning ability to visually discriminate objects was enhanced by the possibility to manipulate them and retain tactile memory; (ii) whether the tactile input differently affected the visual discrimination of object size, shape and surface. Capuchins (N=12) were trained in a two-alternative forced choice task in which they had to visually select the positive stimulus between two wooden objects differing in size, shape or surface. We presented pairs of objects in two experimental conditions: in one condition, capuchins were allowed the manipulation of the chosen object after the visual discrimination (Sight & Touch Condition) whereas, in another condition, they were prevented from haptically exploring the selected object (Sight Condition). We found that capuchins' learning speed was higher in the Sight & Touch Condition compared to the Sight Condition. Moreover, regardless of the experimental conditions, capuchins' learning speed was higher in both size and shape discrimination compared to surface discrimination. Overall, our findings demonstrated that capuchins benefit from the possibility to haptically explore the objects. Tactile information acquired in the course of the experiment allowed high visual accuracy levels to be achieved in a shorter time. This suggests that learning speed strongly depends on the mode of object exploration and it encourages further research on the role of tactile memory in visual discrimination.
