Control of attention before reflexive and intentional saccades

The relation between covert and overt spatial attention and
saccadic eye movements was investigated in control subjects,
Parkinson’s Disease (PD) patients, and cerebellar patients in a
dual-task paradigm. The main question was how different types of
cues (reflexive/intentional) guide the spatial attention during
fixation or during the preparation phase of a saccade. The subjects
were asked to follow a reflexive or intentional cue, to
discriminate a character that appeared either at the cued side
(valid trials) or at the non-cued side (invalid trials), and to
respond by pressing a joystick. The proportion of valid/invalid
trials (cue relevance) was 75/25 and 50/50 for the control
subjects, for the patients only the proportion 75/25 was used. All
discrimination tasks were performed during the preparation of the
saccade to the cued target and also during fixation. The results of
the control subjects showed that discrimination of the character is
always better at the cued side irrespective of the eye movement
condition or the cue relevance, suggesting that spatial attention
is engaged at the cued location even under fixation conditions and
irrespective of the relevance of the cue. The results of the PD
patients point to an intentional saccade impairment that does not
correlate with the overall impairment in the attentional control.
In the double task, also cerebellar patients showed an intentional
saccade impairment that correlates with the deficit in the
attentional control. After these experiments further research could
investigate the impairment of the patients shown here is true for
all cerebellar disorders.