Canonical Size for Real-Word Objects in Drawings Performed under Haptic Control

To date canonical size for physical objects has been exclusively investigated in the visual domain and termed canonical visual size. As the visual and haptic modalities are interconnected in object processing, we have investigated if canonical size occurs in the tactile domain, namely, in embossed drawings made by sighted adults when blindfolded. 17 participants were asked to draw 16 objects of 8 different ranks of physical size. In the visual domain, they drew on sheets of paper, and in the tactile domain, they drew (when blindfolded) on special plastic sheets for embossed graphics haptically controlling the performance with hands. In both the visual and the tactile domain the size of drawings increased linearly with the logarithm of the physical size of real-world objects indicating occurrence of canonical size effect in both domains. Our findings demonstrated that canonical size is not only visual in character but that it is also revealed in a haptic drawing task. It suggests that spatial images (at least visual and tactile) are shared instead of being unimodal in nature.