A world without left
At the University of Birmingham's School of Psychology, researchers investigate one of the most baffling conditions in neuroscience: hemispheric neglect. Medically known as unilateral or hemispatial neglect, it is a disorder of attention, not sight. Following a brain injury—most often a stroke affecting the right parietal lobe—a person can become completely unable to perceive the left side of space. This isn't blindness; their eyes work perfectly. Instead, their brain fails to attend to any information coming from the left. The condition is more frequent and severe after right-hemisphere damage because this hemisphere is dominant for spatial attention and awareness. In the acute stage after a stroke, up to 80% of patients with right-hemisphere damage show symptoms of neglect. The work of influential researchers at Birmingham, such as the late Glyn Humphreys and his wife M. Jane Riddoch, helped researchers understand the complex visual processing deficits that define these conditions.
The effects are deep and counterintuitive. A patient might shave only the right side of his face, eat food from the right side of a plate, or bump into door frames on their left. When asked to describe a familiar location from memory, they will only mention landmarks on the right side of their mental image. The condition can also affect the hearing, smell, and touch. One feature of neglect is anosognosia, a complete lack of awareness that anything is wrong. The patient does not feel like they are missing anything and will deny their deficit, which makes treatment more complicated.
Drawing half a clock
Diagnosing hemispheric neglect often involves simple but pen-and-paper tests. In the Line Bisection Test, a patient is asked to mark the midpoint of a horizontal line. Someone with left neglect will place their mark significantly to the right of the true center. In Cancellation Tasks, patients are presented with a page full of targets (like stars or letters) and asked to cross out all of them; they will consistently ignore the targets on the left half of the page.
Perhaps the most famous diagnostic tool is the Clock Drawing Test. When asked to draw a clock face from memory, a patient with severe neglect might draw a circle but then cram all the numbers—1 through 12—into the right-hand side, leaving the left side completely blank. Another test involves copying simple figures like a star or a flower. The patient will only reproduce the right-sided details. These tests reveal a failure to construct a complete spatial representation of the world. Therapies often focus on forcing the brain to re-engage with the left side of space. One technique, prism adaptation, uses special goggles fitted with 20-diopter lenses that shift the visual field horizontally by about 11.4 degrees. This forces the patient to recalibrate their movements leftward to touch objects, stimulating the brain's damaged attentional networks.