Shifting attention and joint attention dissociation in Williams syndrome: implications for the cerebellum and social deficits in autism.

An experimental paradigm that assesses one's capacity to perform intermodality attention shifting has proved to be sensitive for persons with cerebellar dysfunction. The basic experiment includes three conditions, auditory focus, visual focus and shift attention. In the auditory focus condition, the participant is instructed to press a joystick button when they hear the target tone and to ignore the other tone and the two visual stimuli. In the visual focus condition, the participant is instructed to press only the button to the target colored square and to ignore the other colored square and the two tones. In the shift attention condition, the participant is instructed to press the button to the first auditory target and then to press to the next visual target. They are instructed to continue to alternate their responses between auditory and visual targets until the trial is complete. Three individuals with Williams Syndrome (WMS), a genetic disorder due to the deletion of the elastin gene, were examined under these experimental conditions. Each participant with WMS had previously completed magnetic resonance imaging, and mid-sagittal area measurements had been made of the vermal lobules I-V and VI-VII. Cases were selected on the basis of cerebellar findings: one case was hypoplastic, one was hyperplastic and one had measurements in a range within one standard deviation of average for normal controls. Each of the WMS participants showed a pattern of being impaired in being able to shift their attention rapidly when cue-to-target intervals were less than 2.5 s. Their performance was very similar to previous reports of persons with cerebellar abnormalities and persons with autism. All three participants improved their target accuracy when given more time to shift their attention. The three participants did not experience performance deficits to either long or short cue-to-target intervals in the auditory focus or visual focus conditions. The results are consistent with the presence of cerebellar dysfunction, and are the first to suggest problems with shifting attention in persons with WMS. However, the three WMS participants demonstrated normal joint attention and had none of the social deficits observed in persons with autism.