Hand Rotation Research Articles

Transformation but not generation of motor images is disrupted following stimulation over the left inferior parietal lobe

Motor imagery (MI) involves the generation, maintenance, and transformation of motor images; yet, the neural underpinnings of each stage are not well understood. Here, we investigated the role of the left inferior parietal lobe (IPL) in the stages of MI. Healthy participants (N=20) engaged in a MI task (making judgments about hands presented on a screen; hand laterality judgment task) over two days. Past literature demonstrates the mental rotation of hands in this task involves implicit MI (i.e., where MI occurs spontaneously in the absence of explicit instructions). During the task, active (Day A; 120% resting motor threshold) or sham (Day B; placebo) neuronavigated transcranial magnetic stimulation (TMS) was applied to the left IPL (location determined from past neuroimaging work) on 50% of trials at 250, 500, or 750ms post-stimulus onset, corresponding to different stages of MI. A/B days were randomized across participants. Linear mixed effects (LME) modelling conducted on reaction time and accuracy revealed that longer reaction times were observed when TMS was delivered at 750ms after trial onset, and more greatly for active vs. sham stimulation. This effect was exacerbated for palm- vs. back-view stimuli and for left vs. right hands. Accuracy overall was decreased for active vs. sham stimulation, and to a greater extent for palm- vs. back-view stimuli. Findings suggest that the left IPL is involved in image transformation. Overall this work informs on the neural underpinnings of the stages of MI.

How the Forearm Works.

Hand rotation and the ability to apply force and overcome external load are due to the coordinated activity of forearm bones, the interosseous ligament, and involved muscles. The following review is a detailed description of the anatomy and mechanics which illustrates how the forearm works.

Investigating upper-body muscle activation in different hand rotation angles during push-up variants using OpenSim Musculoskeletal Modeling

Investigating upper-body muscle activation in different hand rotation angles during push-up variants using OpenSim Musculoskeletal Modeling

White matter organisation of sensorimotor tracts is associated with motor imagery in childhood

Despite the important role of motor imagery (MI) in motor development, our understanding of the contribution of white matter fibre properties to MI performance in childhood remains limited. To provide novel insight into the white matter correlates of MI performance, this study examined the association between white matter fibre properties and motor imagery performance in a sample of typically developing children. High angular diffusion weighted imaging data were collected from 22 typically developing children aged 6–14 years (12 female, MAge= 10.56). Implicit motor imagery performance was assessed using a mental hand rotation paradigm. The cerebellar peduncles and the superior longitudinal fasciculus were reconstructed using TractSeg, a semi-automated method. For each tract, white matter microstructure (fibre density, FD) and morphology (fibre bundle cross-section, FC) were estimated using Fixel-Based Analysis. Permutation-based inference testing and partial correlation analyses demonstrated that higher FC in the middle cerebellar peduncles was associated with better MI performance. Tract-based region of interest analyses showed that higher FC in the middle and superior cerebellar peduncles were associated with better MI performance. Results suggest that white matter connectivity along the cerebellar peduncles may facilitate MI performance in childhood. These findings advance our understanding of the neurobiological systems that underlie MI performance in childhood and provide early evidence for the relevance of white matter sensorimotor pathways to internal action representations.

A Regularization-Patching Dual Quaternion Optimization Method for Solving the Hand-Eye Calibration Problem

The hand-eye calibration problem is an important application problem in robot research. Based on the 2-norm of dual quaternion vectors, we propose a new dual quaternion optimization method for the hand-eye calibration problem. The dual quaternion optimization problem is decomposed to two quaternion optimization subproblems. The first quaternion optimization subproblem governs the rotation of the robot hand. It can be solved efficiently by the eigenvalue decomposition or singular value decomposition. If the optimal value of the first quaternion optimization subproblem is zero, then the system is rotationwise noiseless, i.e., there exists a “perfect” robot hand motion which meets all the testing poses rotationwise exactly. In this case, we apply the regularization technique for solving the second subproblem to minimize the distance of the translation. Otherwise we apply the patching technique to solve the second quaternion optimization subproblem. Then solving the second quaternion optimization subproblem turns out to be solving a quadratically constrained quadratic program. In this way, we give a complete description for the solution set of hand-eye calibration problems. This is new in the hand-eye calibration literature. The numerical results are also presented to show the efficiency of the proposed method.

Vision-Based Hand Rotation Recognition Technique with Ground-Truth Dataset

The existing question-and-answer screening test has a limitation in that test accuracy varies due to a high learning effect and based on the inspector’s competency, which can have consequences for rapid-onset cognitive-related diseases. To solve this problem, a behavioral-data-based screening test is necessary, and there are various types of tasks that can be adopted from previous studies, or new ones can be explored. In this study, we came up with a continuous hand movement, developed a behavioral measurement technology, and conducted validity verification. As a result of analyzing factors that hinder measurement accuracy, this measurement technology used a web camera to measure behavioral data of hand movements in order to lower psychological barriers and to pose no physical risk to subjects. The measured hand motion is a hand rotation that repeatedly performs an action in which the bottom of the hand is seen in front. The number of rotations, rotation angle, and rotation time generated by the hand rotation are derived as measurements; and for calculation, we performed hand recognition (MediaPipe), joint data detection, motion recognition, and motion analysis. To establish the validity of the derived measurements, we conducted a verification experiment by constructing our own ground-truth dataset. The dataset was developed using a robot arm with two-axis degrees of freedom and that quantitatively controls the number, time, and angle of rotations. The dataset includes 540 data points comprising 30 right- and left-handed tasks performed three times each at distances of 57, 77, and 97 cm from the camera. Thus, the accuracy of the number of rotations is 99.21%, the accuracy of the rotation angle is 91.90%, and the accuracy of the rotation time is 68.53%, making the overall rotation measurements more than 90% accurate for input data at 30 FPS for measuring the rotation time. This study is significant in that it not only contributes to the development of technology that can measure new behavioral data in health care but also shares image data and label values that perform quantitative hand movements in the image processing field.

Home-based monitoring of persons with advanced Parkinson’s disease using smartwatch-smartphone technology

Movement deterioration is the hallmark of Parkinson’s disease (PD), characterized by levodopa-induced motor-fluctuations (i.e., symptoms’ variability related to the medication cycle) in advanced stages. However, motor symptoms are typically too sporadically and/or subjectively assessed, ultimately preventing the effective monitoring of their progression, and thus leading to suboptimal treatment/therapeutic choices. Smartwatches (SW) enable a quantitative-oriented approach to motor-symptoms evaluation, namely home-based monitoring (HBM) using an embedded inertial measurement unit. Studies validated such approach against in-clinic evaluations. In this work, we aimed at delineating personalized motor-fluctuations’ profiles, thus capturing individual differences. 21 advanced PD patients with motor fluctuations were monitored for 2 weeks using a SW and a smartphone-dedicated app (Intel Pharma Analytics Platform). The SW continuously collected passive data (tremor, dyskinesia, level of activity using dedicated algorithms) and active data, i.e., time-up-and-go, finger tapping, hand tremor and hand rotation carried out daily, once in OFF and once in ON levodopa periods. We observed overall high compliance with the protocol. Furthermore, we observed striking differences among the individual patterns of symptoms’ levodopa-related variations across the HBM, allowing to divide our participants among four data-driven, motor-fluctuations’ profiles. This highlights the potential of HBM using SW technology for revolutionizing clinical practices.

Using a stepper motor as a low-power, low-rotation DC generator for renewable energy harvesting

Currently, the need for renewable energy is getting bigger; studying renewable energy generation requires a small-scale or miniature generator with a low rotation that can produce power for lamp loads. The selection of generators is not as appropriate as using DC motors with high rpm, as generators still produce a small voltage (<12V) and a small current. The use of DC motors equipped with gears requires a large torque to rotate the rotor. The solution offered to overcome this problem is the use of stepper motors as a DC generator with low rotation. The stepper motor has a multi-pole coil and permanent magnet that qualify it as a generator. This study uses the nema23 stepper motor as a DC generator. The stepper motor used is a 6-wire stepper motor (two pairs of coils), a half-wave rectifier, and a capacitor to buffer the voltage. The load is a 12VDC lamp. The results obtained indicate that the stepper motor generator can turn on the lights with a manual hand rotation.

Controlling a Below-the-Elbow Prosthetic Arm Using the Infinity Foot Controller

Nowadays there are various prosthetic arm designs in the literature, the market, and CAD design websites, with different shapes, sizes, and degrees of freedom. Only limited options are available for controlling such prostheses. Prosthetic arm users reported muscle fatigue and unreliability when using the market-dominated myoelectric sensors. This work presents the “Infinity Foot Controller” as a new approach to control a five-finger below-the-elbow prosthetic arm with wrist rotation and bending capabilities. This foot control system receives user input from a custom insole and a sensor-controller unit placed alongside the user’s shoe to perform various hand grips, gestures, and/or rotations. To demonstrate the new foot controller, a design of a 3D-printed below-the-elbow prosthetic arm, called the “Infinity Arm”, is presented. This arm is suitable for gripping relatively lightweight objects and making hand gestures. It includes a wrist actuation system that permits 120° wrist rotation and 70° wrist extension and flexion. It also includes a haptic feedback system that utilizes fingertip force sensors to relay a vibratory response in an armband placed on the user’s arm, giving the user a sense of touch. A proof-of-concept model was built to demonstrate the system and a testing procedure was proposed.

In-situ enhanced anchor-free deep CNN framework for a high-speed human-machine interaction

Human-Robot Interaction (HRI) constitutes a demanding research field that integrates artificial intelligence, informatics, robotics, engineering, and human-machine interaction. In the present era, there is an increased focus on natural user interfaces, with particular attention to gestural modalities. This leads to the coordination of modern robotic systems, where real-time integration and interpretation of manual gestures play a vital role in facilitating effective manipulation. Hand gesture recognition holds a crucial role in the field of machine vision, perhaps greatly exacerbated with varying lighting conditions and backgrounds. In this paper, first an Enhanced Anchor-free Network (EAF-Net) is proposed to perform hand gesture recognition in real-time. The EAF-Net is deep single-stage Convolutional Neural Network (CNN) based architecture. The Custom Precise Prediction Function (CPPF) is utilized for a continuous recognition of a specific gesture from a video feed. Then, the 6-axis collaborative Robot is manipulated using the predicted gesture. The EAF-Net model utilizes the Enriched Hourglass as a backbone feature extraction network. The proposed EAF-Net model undergoes training and assessment using the MITI HD-II dataset. The performance of the model is also analyzed for the standard benchmark datasets (NUSHP-II and Senz-3D). The evaluation of the EAF-Net model’s performance spans a range of IoU values from 0.5 to 0.95. The EAF-Net model led to higher precision values (AP0.5) as 99.22%, recall values (AR0.5) as 98.20%, and F1-Score0.5 as 98.64% on the MITI HD-II dataset. The EAF-Net model consumed a prediction time of 259 ms on NVIDIA Jetson Nano Processor and 14 ms on NVIDIA Titan X GPU. It aided in implementing a portable high-speed 6-axis Robot control framework to pick and place operation in 3D space. The robot would be able to imitate human hand activities such as hand rotation, hand tilting, picking and arranging items, and so on in the near future. Further reduction in prediction time of the model on the portable processors (NVIDIA Jetson Nano, Raspberry-Pi) could enhance the speed of the Human Machine Interaction process.

Visuo-Tactile Congruence Leads to Stronger Illusion Than Visuo-Proprioceptive Congruence: a Quantitative and Qualitative Approach to Explore the Rubber Hand Illusion.

The Rubber Hand Illusion (RHI) arises through multisensory congruence and informative cues from the most relevant sensory channels. Some studies have explored the RHI phenomenon on the fingers, but none of them modulated the congruence of visuo-tactile and visuo-proprioceptive information by changing the posture of the fingers. This study hypothesizes that RHI induction is possible despite a partial visuo-proprioceptive or visuo-tactile incongruence. With quantitative and qualitative measures, we observed that gradual induction of the sense of body ownership depends on the congruence of multisensory information, with an emphasis on visuo-tactile information rather than visuo-proprioceptive signals. Based on the overall measures, the RHI observed went from stronger to weaker with full congruence; visuo-proprioceptive incongruence and visuo-tactile congruence; visuo-proprioceptive congruence and visuo-tactile incongruence; full incongruence. Our results confirm that congruent visual and tactile mapping is important, though not mandatory, to induce a strong sense of ownership. By changing index finger and thumb postures rather than the rotation of the whole hand, our study investigates the contribution of visuo-proprioception and postural congruence in the field of RHI research. The results are in favor of a probabilistic multisensory integration theory and do not resonate with rules and constraints found in internal body models. The RHI could be illustrated as a continuum: the more multisensory information is congruent, the stronger the RHI.

Examination of Football Referees' Attitudes Towards Video Assistant Referee System (VAR) by Q Method

The referees play a crucial role by bearing tremendous responsibility in football. Referees not only manage the football match, but they are also the people who are psychologically affected by the atmosphere of the match and are held responsible for any mistake. This responsibility for the referees seems to have eased somewhat with the development of technology.Yet, unless an evaluation is made from the point of the referees, this situation will remain a mystery. This study aims to evaluate the attitudes of football referees towards the VAR system with the Q method. The methodological model of the study was the Q method, which includes qualitative and quantitative research methods. 25 referees included in the study with the snowball sampling method constitute the study group. The study data were analyzed using the PQMethod 2.35 program, which was developed for Q method studies. The principal component analysis method was used in the analysis of the data. After the analyzes made in the Q method, the data were divided into factors. As a result of principal component analysis and hand rotation afterward, it was seen that the opinions of the participants were gathered under two factors. The questions that the participants gathered under two different factors got higher scores were indicated by their Z scores. The reasons behind it were examined by interviewing the scores obtained from the quantitative data regarding the statements that the participants agreed and did not agree with. As a result, while there is a decrease in the sense of confidence in the referees' VAR system, in themselves and the profession, it is among the results obtained from the opinions that the elimination of injustice is a practice that allows the deserving to win.

Tilt adaptation aftereffects reveal fundamental perceptual characteristics of tactile orientation processing on the hand.

Orientation information contributes substantially to our tactile perception, such as feeling an object's shape on the skin. For vision, a perceptual adaptation aftereffect (tilt aftereffect; TAE), which is well explained by neural orientation selectivity, has been used to reveal fundamental perceptual properties of orientation processing. Neural orientation selectivity has been reported in somatosensory cortices. However, little research has investigated the perceptual characteristics of the tactile TAE. The aim of the current study was to provide the first demonstration of a tactile TAE on the hand and investigate the perceptual nature of tactile TAE on the hand surface. We used a 2-point stimulation with minimal input for orientation. We found clear TAEs on the hand surface: Adaptation induced shifts in subjective vertical sensation toward the orientation opposite to the adapted orientation. Further, adaptation aftereffects were purely based on orientation processing given that the effects transferred between different lengths across adaptor and test stimuli and type of stimuli. Finally, adaptation aftereffects were anchored to the hand: tactile TAE occurred independently of hand rotation and transferred from palm to dorsum sides of the hand, while the effects did not transfer between hands. Our findings demonstrate the existence of hand-centered perceptual processing for basic tactile orientation information. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Advanced aging effects on implicit motor imagery and its links to motor performance: An investigation via mental rotation of letters, hands, and feet.

This study focuses on changes in implicit motor imagery during advanced aging and these changes' co-occurrences with physical motor deficits. We administered a mental rotation (MR) task with letters, hands, and feet to 28 young adults (20-27 years) and to 71 older adults (60-87 years), and assessed motor skills (gait mobility and hand dexterity) and neuropsychological performance. Compared to young adults, older adults showed lower MR performance for all stimuli and stronger biomechanical constraint effects on both hand and foot rotation. Moreover, the foot biomechanical constraint effect continued to increase during late adulthood, and declines in hand and foot motor imagery emerged at earlier old ages than declines in visual imagery. These results first demonstrated distinct aging trajectories of hand motor imagery, foot motor imagery, and visual imagery. Exploratory partial correlation analysis for older adults showed positive associations of low-level perceptual-motor skills (Trail Making Test-A performance) with hand and foot MR performance and positive associations of mobility (Timed Up and Go test performance) with foot and letter MR performance. These associations exhibited somewhat different patterns from those of young adults and raised the possibility that age-related declines in motor (and visual) imagery co-occur with declines in motor functioning.

Develop Control Architectures to Enhance Soft Actuator Motion and Force

Study: Soft robots can achieve the desired range of motion for finger movement to match their axis of rotation with the axis of rotation of the human hand. The iterative design has been used to achieve data that makes the movement smooth and the range of movement wider, and the validity of the design has been confirmed through practical experiments. Limitation: The challenges facing this research are to reach the most significant inclined angle and increase the force generated by the actuator, which is the most complicated matter while maintaining the desired control accuracy. The motion capture system verifies the actual movement of the soft pneumatic actuator (SPA). A tracking system has been developed for SPA in action by having sensors to know the position and strength of the SPA. Results: The novelty of this research is that it gave better control of soft robots by selecting the proportional, integral, and derivative (PID) controller. The parameters were tuned using three different methods: ZN (Ziegler Nichols Method), GA (Genetic Algorism), and PSO (Particle Swarm Optimization). The optimization techniques were used in Methods 2 and 3 in order to reach the nominal error rate (0.6) and minimum overshoot (0.1%) in the shortest time (2.5 s). Impact: The effect of the proposed system in this study is to provide precise control of the actuator, which helps in medical and industrial applications, the most important of which are the transfer of things from one place to another and the process of medical rehabilitation for patients with muscular dystrophy. A doctor who treats finger muscle insufficiency can monitor a patient’s ability to reach a greater angle of flexion or increase strength by developing three treatment modalities to boost strength: Full Assisted Movement (FAM), Half Assisted Movement (HAM), and Resistance Movement (RM).

Correlation analysis of national elite Chinese male table tennis players' shoulder proprioception and muscle strength.

BACKGROUNDShoulder is the most injured part in table tennis players, and it takes multiple roles in transmitting power and striking the center of the ball during the stroke. Proprioception is strongly correlated with high level of athletic performance. It is customary to assume that there is a correlation between proprioception and muscle strength and therefore proprioceptive assessment and rehabilitation is often neglected.AIMTo investigate the correlation between isokinetic muscle strength and proprioception in the internal and external rotation muscle groups of elite Chinese male table tennis players, to provide reference for physical training and rehabilitation of elite table tennis players.METHODSA total of 19 national elite table tennis players from the Chinese National Table Tennis Team were recruited in this research. All of them had more than 10 years training experience and had participated major competitions such as the National Games and World Youth Championships. IsoMed 2000 was used to test the peak torque of internal and external rotation isokinetic concentric contraction of the athletes' bilateral shoulder joints at low speed (60°/s) and high speed (180°/s) respectively; IsoMed 2000 was used to conduct the Joint Position Reproduction test to evaluate the athletes' proprioceptive ability capacity at low speed (60°/s) and high speed (180°/s) respectively. If the data satisfied the normal distribution, the correlation between the differences in peak torque s and angles in different directions was analyzed using a Pearson simple linear model; otherwise, Spearman correlation analysis was used. The comparison of proprioceptive ability between the table tennis racket-holding hand and non-racket-holding hands was performed using independent samples t-test if the data satisfied a normal distribution; otherwise, the Mann-Whitney U test was used.RESULTSThere was no direct linear correlation between the strength and proprioceptive correlation analysis at slow speed (60°/s) and fast speed (180°/s) in the racket-holding hand; At the slow speed (60°/s) and fast speed (180°/s), there was no correlation between muscle strength and proprioception in the non-racket-holding hand except for the internal rotation variable error (VE) and external rotation relative peak torque, which showed a moderate positive correlation (r = 0.477, P < 0.05), (r = 0.554, P < 0.05). The internal rotation’s constant error (CE) and VE were 1.06 ± 3.99 and 2.94 ± 2.16, respectively, for the racket-holding hand, and -3.36 ± 2.39 and 1.22 ± 0.93, respectively, for the non-racket-holding hand; the internal rotation’s CE, VE of the racket-holding hand was lower than that of the non-racket-holding hand, and there was a highly significant difference (P < 0.01).CONCLUSIONThere was no correlation between muscle strength and proprioceptive function in the internal and external rotation of the racket-holding hand’s shoulder in elite Chinese male table tennis players. These results may be useful for interventions for shoulder injuries and for the inclusion of proprioceptive training in rehabilitation programs.

The effect of rheumatoid arthritis on upper extremity functions: A kinematic perspective.

To examine the global upper extremity kinematics in 3D while performing "jar opening motion" in Rheumatoid Arthritis (RA) and to compare these with healthy individuals. Twenty-four women (12 healthy, 12 RA) were included. Evaluations were made with a JAMAR dynamometer, Health Assessment Questionnaire, and 3D kinematic analysis of global upper extremity during "jar opening motion." The time taken during "jar opening motion" was analyzed in 2 parts (Part 1, Part 2), with total time: part 1 + part 2. In addition, shoulder-to-table distance; elbow flexion angle; wrist extension angle; the area scanned and angular rotation by arm, forearm and hand were used in the analysis. Between groups, there was a statistical difference in: bilateral hand grip strength; part 1, part 2, total time; shoulder-to-table distance; elbow flexion angle; the area scanned by hand; angular rotation of arm and hand in favor of the healthy group (P < .05). In stepwise multiple regression analysis, the most predictive variable for disability was elbow flexion, explaining 53.9% of disability. Compared to healthy individuals, individuals with RA have slower motion, more elbow flexion, less hand grip strength, circular pattern in hand, rotation in arm and hand. Increased disability may result in greater load on elbow flexion.

Involvement of the Anterior Nucleus of the Thalamus during Focal Automatisms in Epileptic Seizures: A First Evidence Study.

The Anterior Nucleus of Thalamus (ANT) Deep Brain Stimulation (DBS) has long been touted as the most effective DBS-target for interrupting seizures in focal refractory epilepsy patients. The ANT is primarily involved in cognitive tasks but has extensive reciprocal connections with motor-related regions, suggesting that it is also involved in motor-cognitive tasks. In this work, we aimed to assess the involvement of the ANT during voluntary upper limbs movements. For this purpose, we analyzed Local Field Potentials (LFPs) signals recorded during a movement protocol from one of the first epilepsy patients implanted with a Percept™ PC system, who performed a 5-day period of simultaneous video electroencephalography (vEEG) and Percept PC-LFPs recordings. We estimated time-frequency maps and performed event-related desynchronization (ERD) or synchronization (ERS) analysis and we found that synchronizations found in left hemisphere 7-17 Hz map corresponded to maximum hand rotations. Positive peaks on the ERD/ERS curve occurred at a similar frequency of the hand movements ([Formula: see text] against [Formula: see text]). These results suggested that the ANT may be involved in the execution of automatisms. Moreover, we found that ERD/ERS appeared approximately 2 seconds before the movement onset, as it was found on the EEG of healthy subjects performing the same protocol.

Comparison of Data Classification Results for Leap Motion Recovery Gestures.

Static and dynamic gestures are frequently used in activities supporting learning, recovery healthcare, engineering, and 3D games to increase the interactivity between man and machine. The gestures are detected via hardware devices and data is processed using different software methods. This paper presents the manner of detection and interpretation of two gestures, a hand rotation gesture and a palm closing and opening gesture, using the Leap Motion device. These two dynamic gestures are very often used in hand recovery exercises. For comparing the two gestures we use data classification methods, Support Vector Machine (SVM) and Multilayer Perceptron (MLP). The data for the gesture classification were 80% training data and 20% testing data. The metrics for comparison are precision, recall, F1-score, and the total number of testing cases (support). The SVM classifier gives an accuracy of 99.4% and the MLP classifier a 96.2%. We built two confusion matrices for better visualizing the results.

Mental rotation of hands and objects in ageing and Parkinson’s disease: differentiating motor imagery and visuospatial ability

Motor imagery supports motor learning and performance and has the potential to be a useful strategy for neurorehabilitation. However, motor imagery ability may be impacted by ageing and neurodegeneration, which could limit its therapeutic effectiveness. Motor imagery can be assessed implicitly using a hand laterality task (HLT), whereby laterality judgements are slower for stimuli corresponding to physically more difficult postures, as indicated by a “biomechanical constraint” effect. Performance is also found to differ between back and palm views of the hand, which may differentially recruit visual and sensorimotor processes. Older adults and individuals with Parkinson’s disease (PD) have shown altered performance on the HLT; however, the effects of both ageing and PD on laterality judgements for the different hand views (back and palm) have not been directly examined. The present study compared healthy younger, healthy older, and PD groups on the HLT, an object-based mental rotation task, and an explicit motor imagery measure. The older and PD groups were slower than the younger group on the HLT, particularly when judging laterality from the back view, and exhibited increased biomechanical constraint effects for the palm. While response times were generally similar between older and PD groups, the PD group showed reduced accuracy for the back view. Letter rotation was slower and less accurate only in the PD group, while explicit motor imagery ratings did not differ significantly between groups. These results suggest that motor imagery may be slowed but relatively preserved in both typical ageing and neurodegeneration, while a PD-specific impairment in visuospatial processing may influence task performance. The findings have implications for the use of motor imagery in rehabilitation protocols.