Does visuo-tactile integration affect object discrimination? A comparative study on tufted capuchin monkeys (Sapajus spp.) and kea (Nestor notabilis)

The aim of this study was to investigate in capuchin monkeys (Sapajus spp., N=10) and kea (Nestor notabilis, N=8), two species with acute vision and high manipulative skills, whether tactile input affects their performance in a visual discrimination task. To this end, we assessed if accuracy and/or learning speed in visual modality were enhanced by tactile exploration of the object. Subjects were trained to select the positive stimulus between two cylinders of the same shape, size, but with different surface. One pair of cylinders was inserted in transparent Plexiglas tubes in order to prevent the animals from haptically perceiving the surface of the objects (Sight condition). One pair of cylinders was not inserted in transparent Plexiglas tubes, thus allowing the subjects to perceive the surface both visually and haptically (Sight & Touch condition). Our results demonstrated that both capuchins and kea (i) showed comparable levels of accuracy at the attainment of the learning criterion in the two conditions, but (ii) required fewer trials to achieve the criterion in the Sight & Touch condition compared to the Sight one. Overall, our findings suggest that, in these two phylogenetically distant species, the acquisition of tactile information during manipulative actions facilitates visual discrimination of objects.