## 2 Materials and Methods
### Participant Screening Tests  
The inclusion and exclusion criteria for this study are outlined in Table 1. Potential participants from each group were screened via phone interview to assess if they met the inclusion and exclusion criteria that could be determined with verbal reports. If individuals passed the phone screen interviewing process, they were subsequently evaluated in person in the biomechanics laboratory for the functional screening tests. The Berg Balance Scale (BBS) and Montreal Cognitive Assessment (MoCA) are assessment tools that are valid and reliable in persons with PD [54]. The BBS is a standardized measure that assesses participants' ability to maintain balance during sitting, transfers, and more challenging tasks such as alternating foot taps to stool and standing on one leg [54]. Individuals were excluded from the study if they had a score of less than 36 on the BBS and/or a history of \(>\)2 falls per month, as this identified individuals as fallers or at high risk for falls [54; 55]. The MoCA identifies mild cognitive impairments among the PD population and includes tests of the domains of executive and visuospatial function, memory, language, and attention [56]. A score of less than 21 on the MoCA was an exclusion criterion for this study [56]. Participants also completed a Freezing of Gait Questionnaire (FOG-Q) [57]. There were no participants classified as having FOG based on their responses to question three. Additionally, no participants in either the PD or CON group reported a positive fall history in the past six months.  
\begin{table}
\begin{tabular}{l l} \hline \hline \multicolumn{1}{c}{**Exclusion**} & \multicolumn{1}{c}{**Inclusion**} \\ \hline PD Group & PD Group \\
1. & Surgery or orthopedic injury within 6 months that may \\  & interfere with ambulation (lower extremity joint \\  & replacements, fractures, etc.). \\
2. & Significant medical conditions (unstable hypertension or \\  & heart disease, uncontrolled DM). \\
3. & Vestibular dysfunction within 6 months (BPPV, vertigo, \\  & [PERSON]’s disease, bilateral vestibular loss). \\
4. & Berg Balance Scale (BBS) \(\leq\) 36. \\
5. & Montreal Cognitive Assessment (MoCA) \textless{} 21. \\
6. & Self-report of \(\geq\)2 falls per month. \\
7. & Diagnosis of another neurological disorder besides PD. \\
8. & Deep brain stimulation. \\ \hline CON Group & CON Group \\
1. & Same exclusion criteria as the first six items of the \\  & PD group. \\
2. & Diagnosis of a neurological disease such as PD, multiple \\  & sclerosis, seizure disorder, brain injury, or history \\  & PD group. \\ \hline \hline \end{tabular}
\end{table}
Table 1: Inclusion and exclusion criteria for PD and CON groups.  
Three PD and two CON participants were omitted from data analysis due to an insufficient requisite number of gait cycles during obstacle crossing, e.g., large gaps in marker trajectories. One PD participant dropped out due to back pain on the test day (Figure 2). Participant demographics are presented in Table 2. Additionally, a descriptive summary of participants' self-selected pace walking gait parameters is presented in Appendix A. Scheduled testing appointments for this study aligned with PD participants' \"on\" time in their medication schedule to reflect walking function in their usual medicated state.