Abstract
Patients with lesions to the right parietal lobe often have difficulty recognising unusual or rotated views of objects, while showing intact recognition of canonical views (Warrington & Taylor, 1973). It is not clear whether this represents a pure problem of object identification or whether it is related to impairments in spatial processing which indirectly impinge on the recognition process. In an attempt to answer this question, we delivered transcranial magnetic stimulation (TMS) to the right parietal region while subjects performed a picture-word verification task involving upright and rotated objects. In each trial, subjects viewed a briefly presented (80ms) photograph of a common object, sandwiched between 100ms pattern masks and followed 1s later by a word presented for 500ms. The object could be either in its normal upright orientation, or rotated by 120° in the frontal plane. The subjects had to decide as quickly as possible whether the word named the object or not. A train of 5 TMS pulses was delivered with a frequency of 12Hz to the right posterior parietal lobe, or to a control midline parietal site, starting 120ms after the onset of the object. TMS to the right parietal lobe improved overall recognition accuracy and sped up reaction times for rotated objects. These results confirm a role for the right parietal lobe in processing rotated objects, although they are more consistent with the idea that this brain region is involved in interpreting the spatial attributes of objects rather than playing a critical role in object identification per se.
Supported by grants from the Australian Research Council and The University of Brescia