Right hemisphere dominance: visuospatial awareness and left hemispatial neglect
In most people the right cerebral hemisphere (right side of the brain) leads spatial attention, awareness of where things are around you and of where your body is in space.
Remember
In most people language is led by the left hemisphere and spatial attention by the right. A stroke affecting the right parietal lobe therefore typically causes left hemispatial neglect, in which the patient is less aware of the left side, both of the body and of the space around them.
Memory aid
Left for language, right for space.
It reminds you which hemisphere typically leads each of the two functions.
Cerebral dominance means that one hemisphere takes a greater share of a function, not an exclusive one. In most people, language is led by the left hemisphere and spatial attention by the right. Doctors can use this to predict and locate the cause of a neurological problem.
Visuospatial awareness is knowing where your body is in space and where things are around you. A stroke affecting the right parietal lobe therefore typically causes hemispatial neglect: the patient is less aware of the left side, both of the body and of the space around them.
One widely used idea is that the right hemisphere attends to both halves of space, while the left hemisphere attends mainly to the right half. On that explanation, a right parietal stroke leaves the left side with less attention, since the left hemisphere cannot fully cover for it.
Neglect is a problem of attention and awareness, not of vision or sensation, so a patient with neglect and normal eyesight is not blind on that side. On a clock-drawing task, a patient may leave out the numbers on the left or crowd them together.
Because the left hemisphere is typically dominant for language, aphasia (a loss or impairment of language) points towards the left hemisphere. Dominance is a tendency, not an all-or-nothing rule: most complex activities use both hemispheres, and lateralisation (some functions being better represented on one side) varies between people and between functions.
Key facts
- Dominant sides
- In most people the right hemisphere leads spatial attention, while language is led by the left.
- Visuospatial awareness
- awareness of space and of the body, in which the right hemisphere usually leads.
- Left neglect
- a stroke affecting the right parietal lobe typically causes left hemispatial neglect.
- Not blindness
- ignoring one side of space despite normal vision points to a disorder of attention, not of seeing.
- Clock drawing
- on a clock-drawing task, a patient with left hemispatial neglect may leave out or crowd the numbers on the left.
- Language side
- aphasia (loss or impairment of language) is more likely after left hemisphere damage.
Exam traps
- A right parietal stroke does not cause loss of sensation on the right, because each hemisphere mainly serves the opposite side, so any loss would be on the left.
- Attention to both halves of space is not led by the left hemisphere: in most people the right hemisphere leads, while on a widely used explanation the left hemisphere mainly attends to the right half of space.
- The occipital cortex is the visual centre, so damage there causes a loss of vision in one part of the visual field; ignoring one side of space when vision and visual fields test as normal points to a problem of attention.
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