Copying without perceiving: motor imagery in visual form agnosia.

Patient DF has severely impaired visual contour perception, despite being able to use that same visual information to guide her motor actions. We report that DF has developed a strategy to overcome some of her perceptual deficits. DF was first asked to copy single lines set at different orientations. She performed surprisingly accurately, although her responses were slow. When questioned, DF reported imagining tracing the line with her finger before copying the line on paper, although she was still unable to discriminate perceptually between different line orientations. We found that time restraints, or the requirement to perform secondary concurrent tasks, severely disrupted DF's orientation copying ability. We conclude that DF can use pure motor imagery to compensate for some of her perceptual difficulties.