Pointing to two imaginary targets at the same time: bimanual allocentric and egocentric localization in visual form...

We have previously shown the visual form agnosic patient D.F. has spared sensorimotor utilization of visual information relative to her poor perceptual processing of the same stimulus attributes. Her visuomotor skills are, however, only normal when egocentric visual coding can be used in the task. In other words, her egocentric sensorimotor processing is intact while her 'allocentric' coding of spatial position is impaired. The current investigation extends these previous observations by comparing D.F.'s performance in bimanual pointing to pairs of stimuli directly (the egocentric task) versus pointing to the homologous positions on an adjacent workspace (pantomimed reaching, the allocentric task). The results showed greatly superior pointing accuracy in direct pointing compared to pantomimed pointing. The mechanisms supporting her limited but remaining sensitivity to spatial relationships during pantomimed pointing remain unknown. These residual skills may reflect partially spared categorical coding and/or internal sensorimotor self-cueing.