Neuronal representation of object orientation

The dissociation between object identity and object orientation observed in six patients with brain damage, has been taken as evidence for a view-inva riant model of object recognition. However, there was also some indication that these patients were not generally agnosic for object orientation but w ere able to gain access to at least some information about objects' canonic al upright. We studied a new case (KB) with spared knowledge of object iden tity and impaired perception of object orientation using a Forced choice pa radigm to contrast directly the patient's ability to perceive objects' cano nical upright vs non-upright orientations. We presented 2D-pictures of obje cts with unambiguous canonical upright orientations in four different orien tations (0 degrees, -90 degrees, +90 degrees, 180 degrees). KB showed no im pairment in identifying letters, objects, animals, or faces irrespective of their given orientation. Also, her knowledge of upright orientation of sti muli was perfectly preserved. In sharp contrast, KB was not able to judge t he orientation when the stimuli were presented in a non-upright orientation . The findings give further support for a distributed view-based representa tion of objects in which neurons become tuned to the features present in ce rtain views of an object. Since we see more upright than inverted animals a nd familiar objects, the statistics of these images leads to a larger numbe r of neurons tuned for objects in an upright orientation. We suppose that p robably for this reason KB's knowledge of upright orientation was found to be more robust against neuronal damage than knowledge of other orientations , (C) 2000 Elsevier Science Ltd. All rights reserved.