Final answer:
A right hemisphere brain lesion usually causes severe left neglect due to the fact that each hemisphere controls the opposite side of the body.
Step-by-step explanation:
When there is a lesion in the right hemisphere of the brain, it typically results in severe left neglect. This is because each hemisphere of the brain controls the opposite side of the body. A right hemisphere lesion impairs the individual's ability to attend to and perceive objects on their left side. This can also affect nonverbal aspects of communication such as facial expressions and body language, and may cause the person to exhibit a 'flat affect' in their speech, sounding monotone or lacking emotional expressivity.