Effects of Cognitive Dual-Task on Gait in Parkinson's Disease

Global Cognition Assessed by the Montreal Cognitive Assessment

The assessment of cognitive functions will begin with the evaluation of global cognition. Global cognition will be evaluated using the Montreal Cognitive Assessment (MoCA). The Montreal Cognitive Assessment is a validated scale designed to assess multiple cognitive functions, including attention, concentration, executive functions, memory, language, visuospatial skills, abstract reasoning, calculation, and orientation. The instrument has a maximum total score of 30 points. According to the original validation study, scores of 26 and above are generally considered to represent normal cognitive function, whereas scores below 26 are reported to indicate potential cognitive impairment. For the purpose of this study, an inclusion criterion of a MoCA score ≥ 21 has been established.

Language Function Assessed by the Boston Naming Test

The short form of the Boston Naming Test (BNT), consisting of 15 items (BNT-15), will be used to assess language function. The test comprises images ranging from commonly recognized objects to those that are progressively more difficult to identify. Participants are asked to name the object depicted in each image. If the participant is unable to provide the correct name (e.g., "pelican"), semantic or phonemic cues (e.g., "it is a bird," "pe…") may be provided. The examiner records the type and number of cues required and whether they lead to a correct response. Each correct response is scored as 1 point. The maximum possible score is 15 points, with higher scores indicating better language performance.

Memory Assessed by the Rey Auditory Verbal Learning Test

The Rey Auditory Verbal Learning Test (RAVLT) will be used to assess memory. This test evaluates verbal learning, immediate verbal memory, susceptibility to interference, free recall, and recognition memory. Scoring is based on the number of correctly recalled words in each trial, delayed recall performance, and the number of correctly rejected distractor items during the recognition phase. Higher scores across all indices indicate superior verbal learning and memory capacity, while significant discrepancies between immediate and delayed recall may suggest retrieval or storage deficits.

Visuospatial Function Assessed by the Benton Judgment of Line Orientation Test

The Benton Judgment of Line Orientation Test (JLOT), will be used to assess visuospatial function. The primary aim of the test is to evaluate the individual's ability to perceive, organize, and relate elements within a visual stimulus according to their spatial orientation. The test consists of 30 items, and task difficulty increases progressively as the line segments are shortened from the top or bottom. Scoring is based on paired responses; a point is awarded only if both lines in a pair are correctly identified. Higher scores indicate superior visuospatial perception and spatial relation skills, whereas lower scores may reflect impairments in right-hemisphere mediated spatial organization.

Movement Disorder Society-Unified Parkinson's Disease Rating Scale Part III: Motor Examination (MDS-UPDRS III)

The severity of motor symptoms in patients with Parkinson's disease (PD) will be assessed using Part III (Motor Examination) of the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS). The MDS-UPDRS consists of four parts. Part I evaluates non-motor experiences of daily living with 13 items, while Part II assesses motor experiences of daily living, also consisting of 13 items. Part III focuses on motor examination and includes 18 items assessing motor symptoms. Part IV consists of 6 items evaluating motor complications related to treatment. Each item in the scale is scored on a 5-point Likert scale ranging from 0 to 4, where 0 = normal, 1 = slight, 2 = mild, 3 = moderate, and 4 = severe. In this study, Parts I, III, and IV will be used to obtain descriptive clinical data for individuals with PD.

Anxiety and Depression Assessed by the Hospital Anxiety and Depression Scale

Since anxiety and mood status may influence gait performance, these factors will be evaluated. For this purpose, the Hospital Anxiety and Depression Scale (HADS) will be used. The HADS consists of 14 items and includes two subscales: anxiety (HADS-A) and depression (HADS-D). Each subscale yields scores ranging from 0 to 21. The cut-off points for the Turkish version are 10 for the anxiety subscale (HADS-A) and 7 for the depression subscale (HADS-D).

Static Balance Assessed by the SensorMedica FreeMed Device

Static balance analysis will be performed using the SensorMedica FreeMed (FreeMed, SensorMedica, Rome, Italy) device. The system will be calibrated prior to each assessment. Before testing, participants will be informed about the test procedures. All assessments will be conducted with participants barefoot. Prior to the measurements, participants will be instructed to stand upright, look at a fixed point in front of them, and distribute their body weight evenly on both feet in order to align their center of mass along the midline. For this purpose, participants will be asked to position the point representing their center of pressure, displayed on the device screen, within the marked central cross area on the platform. During the tests, participants will be instructed not to lift or move their feet. Measurements will be performed twice under both eyes-open and eyes-closed conditions, and the mean values will be used for analysis.

Dual-Task Cost

An individual's capacity to perform a dual task is defined as dual-task performance. To determine the impact of dual-task conditions on performance, dual-task cost is calculated using measures such as task accuracy and the time required to complete the dual task. Dual-task cost is expressed using the following formula: Dual-Task Cost = \[(Dual-Task Performance - Single-Task Performance) / Single-Task Performance\] × 100