, 2011) Given the relatively large size of our study compared to

, 2011). Given the relatively large size of our study compared to previous studies, this is unlikely to reflect lack of statistical power. The overall model fitted the data well (F5,19 = 7.996, p = .0003), explaining 82.3% of the variance. The contributions (beta weight values) of each variable in predicting mean time of intention are shown in Fig. 2. The correlation matrix and partial regression

test table are shown in Supplementary Table 2. Regarding specific tic-related factors, we found that tic severity was unrelated to W judgements. Greater capacity for intentional tic suppression was associated with earlier W judgements. Stronger premonitory urges were associated with later W judgements. Regarding general non tic-specific factors, higher ADHD Selleckchem AZD2281 ratings were associated with later W judgements. Greater trial-to-trial variability in judgements of intention (SD W) was associated with earlier W judgements. We fitted the same regression model to the patients’ judgements of the keypress action (M judgements). We did not find any selleck chemicals llc significant associations, and the overall model was far from significant (F5,19 = 0.823, p = .549,

r2 = .178: see Supplementary Table 3). This suggests that the associations reported for conscious intention reflect the specific perceptual ambiguities of volition, rather than interactions between tics and general features of the task, such as using the rotating clock. Interestingly, Casein kinase 1 judgements of keypress actions did not show the significant relation between mean and standard deviation that had previously been

found for judgements of intentions. We suggest that the association between the mean and standard deviation of judgements using the Libet method may reflect individual differences in setting perceptual criteria. For a clear and unambiguous signal such as a keypress, choice of criterion may be more straightforward, and more consistent across individuals. When judging events with a more tenuous phenomenology such as volition, choosing a more liberal criterion will produce an earlier but more variable W judgement. We could not use the same regression model to predict conscious intention in the control group, because they had no scores on the clinical measures. However, our hypothesis that individual differences in criterion setting produce a relation between mean and standard deviation of intention judgements could be tested also in the control group. A simple linear regression confirmed a significant relation in the same direction as for the patients (F1,28 = 4.518, p = .0425). However, this regressor explained around half as much variance (13.9%) as in the patient group (27.9%). This result suggests that the relation between mean and standard deviation of time of intention is driven by a general factor present in both groups. This factor may not be specifically related to tics, although the presence of tics may make its expression stronger.

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