Integration of visuo-tactile information in tufted capuchin monkeys (Sapajus spp.) and kea (Nestor notabilis)

In this study we investigate in capuchin monkeys (Sapajus spp., N=8) and kea (Nestor notabilis, N=8), two species with acute vision and high manipulative skills, whether tactile input affects their performance in visual object discrimination. To this end, we assessed if learning speed and/or accuracy in visual modality were enhanced by tactile exploration of the object surface. Subjects were trained to select one of two PVC cylinders of the same shape and size, but with different textures in two experimental conditions. In the Sight condition the stimuli consisted of two cylinders inserted in transparent Plexiglas tubes in order to prevent the animals from haptically perceiving the texture of the objects. In the Sight & Touch condition the stimuli consisted of two cylinders that were not inserted into tubes, thus allowing the subjects to perceive their textures both visually and haptically. Our results demonstrated that both capuchins and kea (i) required fewer trials to achieve the criterion in the Sight & Touch condition than in the Sight condition, and (ii) showed comparable levels of accuracy in the two conditions at the attainment of the learning criterion. Overall, our findings suggest that, in these two phylogenetically distant species, the acquisition of tactile information during manipulative actions facilitates visual discrimination of objects.