Neuropsychology · Simplified
Neglect or Blindness?
Two people both miss things on the left. One cannot see them. The other can see them perfectly well.
The clinic
Three people, two tasks
Pick who is doing the task and which task they are doing. The drawing is what they produce.
Key terms
- Left neglect
- Failing to attend to the left side of space, or of an object, despite the eyes and visual pathways working normally.
- Left homonymous hemianopia
- Loss of the left half of the visual field in both eyes, from damage to the visual pathway. Attention is unaffected.
- Line bisection
- Marking the midpoint of a horizontal line. The deviation from true centre is the measure.
- Cancellation
- Crossing out every target in a scattered array, with the head and eyes free to move.
What this shows
The eyes are not the problem
Both patients leave things out on the left. Only one of them cannot see the left.
Key idea: Field loss is a problem with the input: part of the visual field is simply not delivered, and a person who knows that can turn their head and look, which is why they find nearly everything on a cancellation sheet even though it takes them longer. Neglect is a problem with attending to a side of space, and turning the head does not help, because the neglected side moves with them. That is why cancellation separates the two while line bisection does not: on bisection both can deviate, and for different reasons. It is also why neglect can appear within a single object as well as within a room, and why a person with neglect will often deny that anything is wrong, which someone who has lost half their field almost never does.
Three fictional profiles, drawn to be clean. Real patients are far less tidy: neglect and field loss frequently occur together after the same stroke, bisection deviation varies with line length and position on the page, and cancellation performance changes with how cluttered the array is and with how the patient is instructed. Some people with field loss compensate poorly and look very like neglect on a single sheet. No single task diagnoses either condition, and nothing here is an assessment instrument or a description of any real person.
The longer version adds two further profiles, scene copying, and the distinction between viewer-centred and object-centred neglect. It is at Visual Neglect Laboratory in the main collection.