Freezing severity and PAC statistics were compared between dual-task and no-task conditions, and stimulation and no-stimulation conditions. Condition-wise freezing severity was measured using three indices: (i) freezing time proportion, referred to as the proportion of the total duration of freezing to the total time spent on walking; (ii) freezing frequency per trial, calculated by dividing the total count of freezing by the total count of trials performed; and (iii) duration per freezing, calculated by dividing the total duration of freezing by the total count of freezing. Condition-wise PAC was calculated by averaging PAC in trials that were performed under the same condition. In analysing the effect of stimulation, we further correlated the stimulation-induced improvement of freezing severity to the stimulation-induced reduction of PAC. The improvement/reduction was normalized by calculating percentage change with respect to the no-stimulation condition for each subject:(2)percentagechange=valueNS−valueSTIMabs(valueNS)×100%Where ‘value’ represents the three indices of freezing severity and PAC, ‘abs’ represents the absolute value, ‘NS’ represents the no-stimulation condition and ‘STIM’ represents the stimulation condition.
