Visuo-tactile information integration in object discrimination: A comparative study on tufted capuchin monkeys (Sapajus spp.) and kea (Nestor notabilis)

In comparative visual cognition research, the influence of information acquired by non-visual senses has received little attention. Among non-visual faculties, tactile input is at least as important as visual input in supplying animals with information about the environment. Systematic studies focusing on how attaining information from different sensory modalities can affect perception are rare in non-human species. Here, we investigate, in two species with acute vision and high manipulative skills, capuchin monkeys (Sapajus spp., N=8) and kea (Nestor notabilis, N=8), whether tactile input can influence the performance in a visual discrimination task. To this end, we assessed if learning speed and/or accuracy in visual modality were facilitated by tactile exploration of the object surface. Subjects were trained to discriminate the positive stimulus of two pairs of PVC cylinders of the same shape and size, but with different textures. One pair of stimuli consisted of two cylinders that were inserted in transparent Plexiglas tubes in order to prevent the animals from haptically perceiving the texture of the chosen object (Sight Condition); the other pair of stimuli consisted of two cylinders that were not inserted into tubes, thus allowing the subject to perceive their textures both visually and haptically (Sight & Touch Condition). 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 the opportunity to acquire tactile information during manipulative actions facilitates visual discrimination of objects.