Chapter 7 talks about the effects of damage to the parietal lobe on one or the other side of the brain. What happens if a patient is unfortunate enough to have bilateral lesions of the parietal lobes (lesions in both cerebral hemispheres)? This condition is rare but it does happen, and the result can be a disorder known as Balint syndrome (named for the doctor who described it in 1909). The disorder has three major symptoms (Driver, 1998):
- Spatial localization abilities are greatly reduced. As a result, a patient with Balint syndrome may have a very hard time trying to reach toward an object.
- Patients with Balint syndrome don’t move their eyes very much. They tend to gaze fixedly ahead.
- Finally, and of most interest for our present purposes, patients with Balint syndrome behave as if they can see only one object at a time. This deficit seems like an extreme form of extinction or neglect, in that attending to one object eliminates everything else.
This inability to perceive more than one thing at a time is known as simultagnosia. (As noted in earlier chapters, agnosia is a failure to know something. Simultagnosia is a failure to know about more than one object simultaneously.)
As discussed in the textbook, even people who are neurologically normal can have trouble binding features together. Remember those pluses in textbook Figure 7.12 that were treated as bundles of red-and-green-and-vertical-and-horizontal until attention sorted out which color went with which orientation? Remember also the demonstration of illusory conjunction in textbook Figure 7.13, where you may have been convinced that you saw a combination of color and form that was not present? Stacia Friedman-Hill, Lynn Robertson, and Anne Treisman found that binding errors of this sort were much more severe in one patient with Balint syndrome whom they tested (Friedman-Hill, Robertson, and Treisman, 1995). This makes sense if you think about combining simultagnosia with a spatial localization deficit. Not only does a patient with Balint syndrome see only one thing at a time, but the features of that “thing” may have come from several different locations in the world.
Driver, J. (1998). The neuropsychology of spatial attention. In H. Pashler (Ed.), Attention (pp. 297–340). Hove, East Sussex, UK: Psychology Press.
Friedman-Hill, S. R., Robertson, L. C., and Treisman, A. (1995). Parietal contributions to visual feature binding: Evidence from a patient with bilateral lesions. Science 269: 853–855.