Cognitive impairments in patients with basal ganglia dysfunction are
primarily revealed where performance relies on internal, voluntary control
processes. Evidence suggests that this also extends to impaired control of
more automatic processes, including visuospatial attention. The present
study used a non-predictive peripheral cueing paradigm to compare and
contrast visuospatial deficits in patients with Parkinson's disease
(PD) with those previously revealed in patients with Huntington's
disease (HD) (Fielding et al., 2006a). Compared
to age-matched controls, both PD and HD patients exhibited increased
distractibility or poor fixation, however only PD patients responded
erroneously to cue stimuli more frequently than control subjects. All
subjects demonstrated initial facilitation for valid versus
invalid cues following the shorter stimulus-onset asynchronies (SOAs) and
a performance decrement at the longer SOAs (inhibition of return),
although there was a clear differentiation between these groups for
immediate SOAs. Unlike both control and PD subjects, where IOR manifested
between 350 and 1000 msec, IOR was evident as early as 150 msec for HD
patients. Further, for PD patients, spatially valid cues resulted in
hyper-reflexivity following 150 msec SOAs, with saccadic latencies shorter
than those generated in response to un-cued targets. Thus contrasting
deficits were revealed in PD and HD, emphasizing the important
contribution of the basal ganglia in the control of more automatic
behaviors (JINS, 2006, 12, 657–667.)