Rigid And Nonrigid Objects In Canonical And Noncanonical Views: Hemisphere-Specific Effects On Object Identification

Abstract

We compared the performance in a picture-name matching task of 10 patients suffering from left cerebral hemisphere (LH) damage and 10 from right hemisphere (RH) damage. The tasks showed detailed figures of nonrigid objects (animals) and rigid objects (artefacts), and each object was shown in two separate views: a noncanonical view (an unusual perspective for rigid objects or a contorted pose for the nonrigid ones) and a canonical view (a typical perspective and pose). Patients with LH damage were specifically impaired in identifying noncanonical (contorted) poses of nonrigid objects (animals). In a second picture-name matching experiment, using the divided visual field technique, normal subjects matched names to images of nonrigid shapes (animals) shown in canonical and noncanonical perspectives of noncontorted, typical poses of the animals. It was found that the normal subjects' RH identified these perspectives better than their LH. We conclude that computationally different problems are solved by different cerebral mechanisms when identifying flexible objects and when identifying rigid objects. We propose the idea that identifying flexible objects when their shapes contort relies on accessing stored descriptions of objects' parts and their “categorical” spatial relations and that both types of information are encoded better by the LH. In contrast, we propose that the RH is more adept at identifying different perspectives of rigid objects (and flexible objects when their shapes do not contort) because of this hemisphere's superiority in encoding specific global shapes and their views, and in coordinate spatial transformation.