Agnosia for object orientation: naming and mental rotation evidence

We have previously reported the performance of a patient (NL) who could recognize objects, but appeared to lack knowledge of their orientation. These results were interpreted as evidence that NL had isolated access to a viewpoint-independent (ventral stream) object recognition system. However, because NL's responses on naming tasks were not timed, it was not possible to establish whether he showed the same pattern of reaction time performance generally accepted as evidence of a 'mental rotation' strategy in neurologically normal subjects. Here we report NL's performance on two reaction time tasks, testing his ability to transform images when naming, and discriminating between rotated mirror image objects. As predicted, and in contrast to normal volunteers, NL showed no 'mental rotation' effect in his naming of misoriented objects. Paradoxically, he performed well on a traditional Shepard and Metzler mental rotation task. He also showed a normal orientation effect when dealing with misoriented faces. These findings offer further support for viewpoint-independent theories of object recognition, and bolster the claim that object orientation knowledge can be regarded as, in some respects, a special class of spatial information.