Visual neglect, also known as hemispatial neglect or unilateral neglect, is a neuropsychological condition where a person fails to attend to or acknowledge stimuli on one side of space, despite having intact vision. The disorder is not caused by blindness or a simple visual field cut, but rather a failure of attention and spatial awareness. This loss of awareness is typically directed toward the side of space opposite a brain injury, most commonly resulting in the neglect of the left side. It is a disorder of higher visual processing, meaning the eyes can physically see, but the brain does not consciously process or register the information.
How Visual Neglect Manifests
The effects of visual neglect are observable in many daily activities. A person may only eat food from the right half of a plate, leaving the left side untouched, or only shave or apply makeup to one side of their face. When reading, they might consistently skip the beginning of lines, or when drawing, they may only reproduce the right half of an object, like a clock or a house.
Patients frequently bump into obstacles on the neglected side because they are unaware of their presence. This lack of awareness often leads to anosognosia, a condition where they are unaware of their own deficit. They truly believe they are seeing the whole world and may become confused when others point out their omissions.
The manifestations can be divided into sensory and motor forms. Sensory neglect involves failing to notice or respond to things on the affected side. Motor neglect, sometimes called directional hypokinesia, means the person fails to use a limb on the affected side, even if the limb has preserved strength and movement. The issue is a failure to initiate movement toward the neglected space.
The Neurological Foundation
Visual neglect is typically a consequence of acute brain injury, with stroke being the most frequent cause. The damage is most often located in the right cerebral hemisphere, which results in neglect of the left side of space. Lesions to the posterior parietal cortex, the superior temporal lobe, and the insula are commonly implicated.
The right hemisphere plays a dominant role in attending to space on both the left and right sides. In contrast, the left hemisphere primarily manages attention only to the right side of space. When the right hemisphere is damaged, the left hemisphere cannot fully compensate for the loss of attention to the left side, leading to the severe left-sided neglect seen in most cases.
Damage to the right hemisphere causes an attentional bias that pulls the person’s focus toward the right side. This imbalance in spatial processing defines the syndrome, rather than damage to the primary visual pathways. While neglect can occur following left hemisphere damage, it tends to be less common and less severe, supporting the theory of right hemisphere dominance for global spatial attention.
Identifying Visual Neglect Through Testing
Clinicians use specific, observable tests to confirm the presence of neglect and distinguish it from simple visual field loss, or hemianopia. Cancellation tasks are sensitive measures, requiring the patient to find and mark specific targets scattered across a page. A patient with neglect will consistently omit targets on the side opposite the brain lesion, often failing to acknowledge that side of the page exists.
The line bisection task is another common bedside test, where the patient is asked to mark the center of several horizontal lines. Patients with neglect will typically bisect the lines too far toward the non-neglected side, demonstrating a shift in their subjective center of space. Copying tasks, such as asking the patient to draw a clock or a house, reveal neglect when the patient omits or compresses the details on the neglected side.
These tests help quantify the degree of spatial bias, but functional scales are also used to assess the impact on daily activities. The disorder is a pervasive functional disability that affects personal, peripersonal, and extrapersonal space. Diagnosis relies on a combination of these tests and observation of real-world behavior.
Strategies for Recovery
Rehabilitation for visual neglect aims at retraining the brain to attend to the neglected side of space and improving functional independence. Visual scanning training is a common approach, which involves cueing the patient to consciously turn their head and eyes toward the affected side. This technique encourages systematic exploration of the neglected space, helping to counteract the attentional bias.
Limb activation training is another strategy, encouraging the patient to actively move the arm or leg on the affected side into the neglected space. This movement helps to draw attention and increase awareness to that side of the body and the surrounding area. Both visual scanning and limb activation training can lead to improvements in neglect symptoms.
Prism adaptation involves having the patient wear specialized glasses that shift the visual field to the right. The patient must then make pointing movements toward targets, which initially results in errors due to the visual shift. The brain adapts to this shift. Upon removal of the prisms, the patient temporarily exhibits a beneficial after-effect, causing their attention and movements to drift leftward. This leftward recalibration helps to counteract the neglect bias, with benefits that can sometimes last for months after the treatment ends.