To assess whether there is indeed evidence for global endogenous saccadic facilitation in PD, we used the same dual task paradigm to measure voluntary saccade production PF-562271 with and without a perceptual discrimination task. The PD and control subjects that comprised the groups in the earlier report (van Stockum et al., 2011b) [20 PD patients (eight females) and 20 control participants (eight females)] performed the

voluntary saccade tasks. The groups were matched for mean age and years of education. Mean age in the PD group was 65.0 years, ranging from 50 to 77. In the control group the mean age was 65.5 years, ranging from 56 to 76. Hoehn & Yahr scores in the PD group ranged from 1 to 3. To exclude subjects with dementia, only participants who scored 25 or more on the Montreal Cognitive Assessment (Nasreddine

et al., 2005; Dalrymple-Alford et al., 2010) were included. The Movement Disorder Society-sponsored revision of the Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) was used http://www.selleckchem.com/products/cx-5461.html to assess motor impairment in the PD group (Goetz et al., 2008). The participants in the PD group were tested ‘on’ medication; see Table 1 for demographic details of the PD group. This project received ethical approval from the Upper South A Regional Ethics Committee of the New Zealand Ministry of Health and participants gave informed consent. The paradigm was adapted from Deubel (2008), with saccades performed with and without a concurrent two-alternative forced choice (2AFC) perceptual discrimination task (van Stockum et al., 2011b). Four potential saccade targets were displayed throughout each trial and the onset Methocarbamol of a central arrow cue indicated which of the four was the saccade target. This procedure ensured that the task elicited voluntary saccades (the saccade target was not exogenously determined by the appearance of a peripheral visual stimulus), without the need to suppress

a reflexive saccade. The 2AFC discrimination task required participants to report the identity of a symbol (E or 3), which appeared for 100 ms at the target location shortly (the stimulus onset asynchrony or SOA) after the onset of the arrow cue. The SOA and the duration of the discrimination symbol were such that the discrimination symbol generally disappeared before saccade onset and therefore the E or 3 was not foveated directly. Exactly the same trials were presented (albeit in a different order) for the saccade task ‘without discrimination’ and the saccade task ‘with discrimination’. Only the instructions to the participants differed: in the task ‘without discrimination’, participants were instructed simply to ‘look at the target indicated by the arrow as quickly and accurately as possible’ and to ignore any flickers they might notice in the display, as they were irrelevant to the task.