A window to the brain

Research on a rare visual-spatial disorder is enhancing scientists' understanding of how the mind works and providing "a window on mapping the brain," according to James Hoffman, UD professor of psychology.

Hoffman is conducting the studies on children with Williams syndrome. About one in 25,000 babies is born with the genetically based condition, which results in mild mental retardation and an unusual pattern of strengths and weaknesses in cognitive abilities. Individuals with the syndrome may have typical language and social skills but still be profoundly impaired in their visual-spatial abilities and numeric processing.

For example, an 11-year-old child with Williams syndrome may be unable to draw a picture of a ball with two colors but may have no difficulty describing it.

Hoffman and Barbara Landau of Johns Hopkins University are using eye-tracking measures to detail the nature of the spatial deficit and how it affects descriptive language. The goal of their work is to understand more completely how the brain is organized.

Hoffman's research centers on spatial cognition, particularly visual attention and eye movements. He focuses on the role of attention in the performance of such "real-world tasks" as searching for an object in a cluttered scene or constructing spatial patterns.

He uses standard models from cognitive psychology, as well as measuring "event-related brain potentials" and eye movements.

In their labs, Hoffman and Landau work with children of various ages with and without Williams syndrome and show them images on paper, such as the two-colored circle.

The researchers ask the children to reproduce those pictures, and the youngsters' eye movements are recorded as they try to complete the task. Tracking the eye movements, Hoffman says, gives researchers an understanding of how the brain is working and of the nature of the deficit.

He says he and Landau have pinpointed a variety of deficits and areas of the brain that are responsible for performing spatial tasks. They now are trying to understand at what point the brain malfunctions in persons with Williams syndrome, either in observing the object or in reproducing it, and why.

"These kids are giving us a window on mapping the brain/mind," Hoffman says.

Despite their inability to reproduce images on paper, he notes, those with the syndrome are able to recognize and identify objects and to describe them clearly in words.

"We believe that the spatial distortions we see in drawings and other visio-spatial construction tasks by people with Williams syndrome do not reflect corresponding distortions in their perception of the world," Hoffman says.

"We argue that this syndrome leaves spared a number of spatial cognitive subsystems, including object recognition and identification, biological motion perception and spatial language ... and that some of the most profound deficits are not due to abnormal architecture but to small misadjustments that culminate in large, downward-spiraling performance."

One example of this, he says, is that the children with Williams syndrome know that their drawings are not correct, with their most common error involving choosing an incorrect part of the picture and drawing it in an incorrect location. They can easily distinguish between correct and incorrect drawings of models, but they cannot do better when they try again, he says.

He adds that the deficit is not simply a problem with motor skills, because the children have no difficulty tracing the drawings correctly.

"Drawing or assembling parts to make a model is an extremely frustrating experience for them because they are aware of their poor abilities in this domain, and they usually resort to random changes in an attempt to correct their efforts," Hoffman says.

"Their spatial deficits are not due simply to problems in either input (perception) or output (action) but to some cognitive processes in between. We are now trying to characterize the nature of these processes."

The research is funded by grants from the March of Dimes, National Science Foundation and National Institutes of Health.

--Barbara Garrison