Developing Intelligence has an interesting look at a brain-injured patient from the medical literature who can identify objects, but can’t locate them.
RM suffered two strokes, damaging both sides of his occipito-parietal cortex (see the image above). This region of the brain is known to be important for spatial computations; this pattern of damage will often result in Balint’s Syndrome, characterized by three primary problems: the inability to perceive more than one object at a time (simultagnosia), the inability to reach towards objects that are being focused on (optic apraxia), and severe problems in changing which object the eyes are focused on (optic ataxia). Such patients are essentially blind outside the focus of their attention, and cannot locate, reach for, or track the spatial movements even of items that are within their focus of attention. In some ways, this represents the complete dissolution of spatial awareness; Robertson quotes a description of Balint’s “as if there is no there, there.”
The article suggests that the brain damage may have a caused a problem in ‘visual binding’.
The ‘binding problem‘ is the question about how the brain can process different aspects of an experience in different parts, but we still get an impression of a single combined perception.
For example, we know that colour is largely processed in an area of the visual cortex called ‘V4′ and motion processed in an area called ‘V5′, yet unless we suffer brain damage, we just experience a moving coloured object as a single experience.
Somehow, these different processes are combined into our conscious experience. It’s still a mystery, but patients like the one discussed in the Developing Intelligence article are giving us important insights into how the brain does the job, by seeing how it breaks down after injury.
The article also makes the interesting suggestion that while Balint’s syndrome and similar disorders might be the visual binding system not working properly, synaesthesia, where the senses are combined, might be visual binding working too hard.
Chris goes on to explore this idea in more detail, in a further article that looks at the research on visual binding in people with synaesthesia.