Reply to: Touchscreen Smartphone Interaction in Parkinson's Disease and Healthy Subjects on Out‐Patient Clinics

We thank López-Blanco et al1 for their interest in our recent findings on touchscreen skills in patients with Parkinson's disease (PD),2 highlighting the importance of this topic and the increased use of touchscreen devices in current society and in healthcare. In their own study, the authors did not find differences in touchscreen performance between PD patients on medication and healthy control subjects (HC) despite a variety of tasks used. Similar to our findings, timing parameters did not differ between groups when tapping and sliding in a single direction.2 In contrast, we found a significantly slower performance when sliding in multiple directions in PD patients compared to HC even when on medication and increased slowing of specific tasks when off. Moreover, PD patients had a worse tapping accuracy than HC on medication, similar to previous work.3, 4 López-Blanco et al1 ascribed these between-study discrepancies to touchscreen interface settings, disease characteristics, and the number of task repetitions. López-Blanco et al1 questioned the ecological meaning of the multi-direction sliding tests used in our study and the significance of touchscreen performance slowing for daily use. Multi-direction sliding on a touchscreen is a complex manipulation, which we believe is highly relevant for daily life. For instance, a touchscreen unlock trace requires sliding motions in multiple directions5 as do specific search functions on a smartphone. Although slower performance might not necessarily impede the efficient use of mobile devices, we contend that during daily tasks time constraints frequently cause stress and anxiety, for example, when having to find information quickly. As such, slowing is likely to affect patients' smartphone proficiency during functional tasks. Additionally, turning off an alarm requires fast responses, via double tapping or sliding a circle toward a target (test 3-4 of López-Blanco et al).1 Although neither study found between-group differences in inter-tap interval time and single sliding time when on medication, we expect that, particularly when off, PD patients will be hampered when turning off alarm clocks or medication reminders.2 When off medication, Wissel et al4 demonstrated a significantly slower inter-tap interval time than HC in PD patients with worse disease severity than included in our study. This predicts that more affected patients will experience even greater problems. We did not suggest that on the basis of our findings touchscreen technology should be disregarded in PD.2 Instead, we claimed that even basic touchscreen skills cannot be assumed to remain unaffected by the disease and that this needs to be taken into account. As medication only had limited effects, we also recommended developing training programs targeting touchscreen manipulations, which may become even more functionally useful than writing training programs with time. To conclude, we agree with López-Blanco et al1 that in future work laboratory touchscreen tests need to be extended to real life touchscreen manipulation tasks, requiring both motor and cognitive flexibility. Ideally, such study should include larger PD samples with more diverse motor and cognitive capacity. (1) Research Project: A. Conception, B. Organization, C. Execution; (2) Statistical Analysis: A. Design, B. Execution, C. Review and Critique; (3) Manuscript Preparation: A. Writing of the first draft, B. Review and Critique. J.D.V.: 1C, 2A, 2B, 3A A.N.: 1A, 2C, 3B E.N.: 1A, 1B, 1C, 2A, 2C, 3C This study was approved by the local ethics committee UZ/KU Leuven according to the code of Ethics of the World Medical Association (Declaration of Helsinki, version 2013, S61793). Before participation in the study, an informed consent form was signed after explanation of the study protocol. We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines. The work presented in this manuscript was supported by the Research Foundation Flanders—FWO (12F4719N, 1,520,619 N, G0A5619N) and King Baudouin Foundation (J1811020-E003). The authors declare that there are no conflicts of interest relevant to this work. E.N. is a postdoctoral fellow funded by the Research Foundation Flanders—FWO (12F4719N).