You can also diagnose neglect with some simple tests. Have the subject copy or draw from memory a flower or other object, and she will draw only half of it (c). Strangely, this half-drawing effect is true even if she works with her eyes closed, implying that she is even neglecting the left half of the object that she conjures in her head. (Our colleague Stuart Anstis has requested that if he ever develops neglect from stroke, we ensure his Botox series continues on both sides of his face!)
When asked to draw a clock, the patient draws only half of it. The entire circle is drawn—partly because this is an overlearned “ballistic” response that does not require focused attention. But she packs the 1 to 12 on the right half of the clock (d) or inserts only 1 to 6.
Ask her to bisect a horizontal line; her bisector is way off to the right because she is bisecting the right half of the line. Now you might think that if the horizontal line is moved entirely into her right (nonneglected) side, she would bisect it accurately. But she does not. Even if her plate of food is moved entirely into her nonneglected right visual field, she continues to eat the food only on the right side of the plate. In addition to neglecting the left side of her visual world, she neglects the left sides of objects even if they are entirely on her right.
There is no sharp line going down the center of the visual field separating the neglected left and the nonneglected right. We should think, instead, in terms of a gradient of neglect. This effect is different from what one sees when the right visual cortex—rather than right parietal lobe—is damaged. In this case, the result is a sharp boundary between the blind region on the left and the intact right region of the visual field. And of course, the subject cannot see objects on her left even if she is forced to “attend” to the blind region. She can no more see these items than she can see behind her head.
Annihilation of the Left
A curious aspect of neglect is that the patient is largely unaware of it. He neglects the neglect! At some level, he may be dimly aware that something is wrong, telling us he “needs glasses.”
Sally’s obliviousness to her neglect suggests yet again that what she has is not merely a sensory deficit or blindness to visual input coming from her left nor even just a failure to attend to the left. We should think of it instead as an existential annihilation of the left side of the universe. For her, “left” has simply ceased to exist. Maybe she even has problems with abstract ideas or words that require the use of the word “left,” but we have not tested this idea.
Extraordinarily, neglect patients may be even unaware of the paralysis of their left arm, a condition called anosognosia. When we asked Sally to touch her nose with the nonparalyzed right hand, she did so. When asked if she could move her left hand, she said, “Yes, I can move it fine.” But when we then asked her to touch her nose with her left hand, she promptly grabbed the lifeless left hand with her right and raised it toward her face using it as a “tool” to touch her nose! Clearly, even though “she” (the conscious person) was unaware of the paralysis, some part of the brain “knew” the left arm was paralyzed. Why else would she unhesitatingly grab it and raise it toward her nose?
The inadvertent humor of her response was lost on her. Bear in mind that in every other respect she was completely lucid, intelligent and articulate. The full implications of neglect were brought home to us even more vividly when we hung a two-foot-by-two-foot mirror on the wall to her right. When she turned her head to the right to look in the mirror, she saw her face and, of course, reflections of objects on her left that she had been neglecting. She “knew” she was looking at her face in the mirror. But our question was, Would the mirror “correct” her neglect by making it obvious to her that there was a whole world on the left that she had been ignoring?