Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor and cognitive impairments that substantially reduce functional independence, social participation, and quality of life. A key psychosocial factor affected by these impairments is self-efficacy, defined as an individual's belief in their ability to successfully perform tasks and achieve personal goals. In people with PD, reduced self-efficacy is closely associated with motor dysfunction, cognitive decline, fear of falling, depressive symptoms, and decreased motivation for physical and social activities. These factors interact in a bidirectional manner, creating a negative cycle in which poor confidence limits participation, further accelerating functional deterioration.

From a neurophysiological perspective, the degeneration of dopaminergic neurons in PD disrupts the automatic control of movement. As a consequence, individuals with PD rely more heavily on cognitive and attentional resources to execute daily motor activities. This reliance becomes particularly problematic in dual-tasking situations, where two tasks must be performed simultaneously, such as a motor task combined with a cognitive task or two concurrent motor tasks. Because attentional capacity is limited, dividing attention across tasks frequently results in performance declines in one or both tasks, a phenomenon referred to as dual-task interference or dual-task cost. Low confidence when facing these situations may reinforce avoidance behaviors, thereby further diminishing physical activity and community engagement.

Dual-task training has been proposed as a rehabilitation strategy to improve functional performance, self-efficacy, and daily functioning in people with PD. However, important gaps remain in the evidence. It is currently unclear whether motor-cognitive or motor-motor dual-task training is more effective, particularly when considering the presence or absence of cognitive impairment. Additionally, the relative impact of secondary cognitive versus secondary motor tasks on primary motor task performance has not been well established. Another unresolved issue concerns attentional prioritization strategies during dual-task training. Fixed-priority strategies require individuals to attend equally to both tasks, whereas variable-priority strategies involve alternating attention between tasks. The optimal strategy for individuals with PD, especially those with cognitive deficits, remains unknown.

The proposed research aims to address these knowledge gaps by systematically evaluating the effects of different dual-task training modalities and attentional prioritization strategies on self-efficacy, functional performance, and quality of life in individuals with PD, both with and without cognitive impairment. An additional objective is to investigate whether improvements in dual-task performance are associated with reduced attentional demands, as reflected by decreased activity in the prefrontal cortex, which is considered a key neural marker of cognitive load during task performance.

The research program comprises two complementary studies. Study 1 is a randomized clinical trial with a factorial design stratified by cognitive status. Participants with PD are randomly assigned to one of four intervention groups combining dual-task modality (motor-cognitive or motor-motor) with attentional strategy (fixed-priority or variable-priority). All participants undergo baseline assessments conducted by an interdisciplinary team and complete 24 individualized training sessions over an eight-week period. Outcome measures include self-efficacy, motor and cognitive performance, quality of life, dual-task cost, and prefrontal cortex activity. Study 2 uses a cross-sectional design that includes individuals with PD from study 1 and a matched group of healthy older adults. Using identical assessment procedures, this study compares dual-task interference and prefrontal cortex activity between people with PD and healthy controls, providing additional insight into disease-specific cognitive-motor interactions. Overall, this research seeks to inform evidence-based, personalized rehabilitation strategies by identifying the most effective dual-task training approaches for improving confidence, functional ability, and quality of life in individuals with PD.

Participants diagnosed with idiopathic Parkinson's disease confirmed by a neurologist will be recruited in this study. Inclusion criteria will be:

1. Hoehn & Yahr stages I, II or III
2. Participants with no or mild to moderate neurocognitive impairments
3. Participants with and without symptoms of depression
4. Able to walk independently
5. Unaltered dose and type of medication up to three months before the commencement of the study
6. Participants able to understand and respond to the instructions given in the study.

Exclusion criteria will be:

1. The presence of any other concomitant neurological, musculoskeletal disease
2. History of leg or brain trauma or surgery
3. Vision or hearing problems that may affect the performance of cognitive tests
4. Clinical diagnosis of major neurocognitive disorder