Hemispatial neglect in the city of Milan: The relationship between mental representations and hemispatial neglect

Unilateral neglect and mental representations

Hemispatial neglect (also known as unilateral neglect) is an illness frequently encountered in clinical settings. Much of it is caused by stroke and presents the symptom that spatial cognitive abilities on either the left or the right side (most often the right) are significantly reduced.

Although the retina, which is the entrance for visual processing, and the visual cortex, which is the entrance for visual processing in the brain, are not damaged, damage to the parietal lobe, which integrates information, and the nerve fibers that communicate with it cause the symptom that the patient cannot see, does not notice, and does not know about either the left or the right side, even though they can see it. So, what images make up the mental representations when patients close their eyes?

The paper that I discuss today concerns a study of patients with unilateral neglect who had lived in Milan, Italy for a long time. Researchers had patients think about the Duomo that is the symbol of the city and recall what they could see under conditions such as:

• the buildings, shops, and structures they could see when looking at Milan from the entrance to the Duomo;
• the buildings, shops and structures they could see when looking at Milan from the plaza in front of the Duomo, facing the Duomo;
• the furniture and objects they could see when sitting in the chair in the office where they had worked for many years; and
• the furniture and objects they could see when facing the office chair from the other side.

Fascinatingly, the patients could not properly recall the left side when they remembered scenes that they could not see directly, just like with the symptoms of left hemispatial neglect, and they had not forgotten the left half, because they recalled the neglected left half (that is, the right half when looking from the opposite side) when remembering the scene from the opposite perspective.

I wondered whether the visual experience that we believe we can usually see is really an image translated in our heads, and thought that the difference between what we can see and what we remember might not be that big.

Reference URL: Unilateral neglect of representational space.

Two patients showing left unilateral neglect were asked to describe imagined perspectives of familiar surroundings. Left-sided details were largely omitted in the descriptions. Some theoretical implications of the occurrence of unilateral neglect in representational space are briefly considered.