25 - Representations of the Parietal Lobe II

Question 1

What is hemispatial neglect?

Answer 1

• Patient’s vision seems fine
• But when asked to replicate a drawing they seem to neglect one half of the image.

Neglect – attention to one side is impaired

Right parietal stroke leads to impairment on left side

Question 2

How do people with strokes in the right parietal lobe use imagery when describing familiar places?

Answer 2

• Imagery uses signals going from allocentric memory map to parietal visual areas (egocentric)
• Imagining the piazza, they wouldn’t describe any buildings on the left.
• Memory of both sides of piazza intact
• When projected into egocentric person-centred coordinates, left side neglected.

Question 3

What’s the difference between stimulus-centred and object-centred coordinate systems for object recognition?

Answer 3

Stimulus-centred
- To recognise arrow as right-pointing or left-pointing etc., arrow, need to calculate location of arrowhead relative to its centre, not relative to overall visual field.

Object-centred
- To recognise words, need to know which letter is first, which second, etc., even for unusual word orientation.

Question 4

What do studies on imagination in people with right parietal lobe strokes suggest about memory maps in these patients?

Answer 4

Their memory map is intact, but half neglected

Imagery uses the same mechanism which causes neglect of real stimuli

Means the memory map must be elsewhere in the brain, gets unpacked in the parietal cortex

Question 5

On studies on neglect in people with right parietal lobe strokes, what kind of stimuli is still processed?

Answer 5

• Meanings (e.g. house on fire, choose house not on fire even though they can’t say they saw it)
• Words still read (even if neglected)
• Imagery still works (but half neglected)

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