Can you hear shapes you touch?

Shape is an inherent property of objects existing in both vision and touch but not audition. Can shape then be represented by sound artificially? It has previously been shown that sound can convey visual information by means of image-to-sound coding, but whether sound can code tactile information is not clear. Blindfolded sighted individuals were trained to recognize tactile spatial information using sounds mapped from abstract shapes. After training, subjects were able to match auditory input to tactually discerned shapes and showed generalization to novel auditory-tactile pairings. Furthermore, they showed complete transfer to novel visual shapes, despite the fact that training did not involve any visual exposure. In addition, we found enhanced tactile acuity specific to the training stimuli. The present study demonstrates that as long as tactile space is coded in a systematic way, shape can be conveyed via a medium that is not spatial, suggesting a metamodal representation.