Papers by Mark Mon-Williams
PLOS ONE, 2021
Purpose Many people experience unilateral degraded vision, usually owing to a developmental or ag... more Purpose Many people experience unilateral degraded vision, usually owing to a developmental or age-related disorder. There are unresolved questions regarding the extent to which such unilateral visual deficits impact on sensorimotor performance; an important issue as sensorimotor limitations can constrain quality of life by restricting ‘activities of daily living’. Examination of the relationship between visual deficit and sensorimotor performance is essential for determining the functional implications of ophthalmic conditions. This study attempts to explore the effect of unilaterally degraded vision on sensorimotor performance. Methods In Experiment 1 we simulated visual deficits in 30 participants using unilateral and bilateral Bangerter filters to explore whether motor performance was affected in water pouring, peg placing, and aiming tasks. Experiment 2 (n = 74) tested the hypothesis that kinematic measures are associated with visuomotor deficits by measuring the impact of smal...
The Journal of Headache and Pain, 2020
Background Trigeminal neuralgia (TN) is an orofacial condition defined by reoccurring, spontaneou... more Background Trigeminal neuralgia (TN) is an orofacial condition defined by reoccurring, spontaneous, short-lived but excruciating stabbing pain. Pharmacological interventions constitute the first-line treatment for TN, with antiepileptic drugs commonly prescribed. People treated for TN pain with antiepileptic drugs describe cognitive and motor difficulties affecting activities of daily living, and report poorer quality of life. We undertook the first comprehensive objective evaluation of sensorimotor and cognitive performance in participants being treated for TN pain with antiepileptic drugs relative to age-matched controls. Methods Participants (43 TN, 41 control) completed a battery of sensorimotor (steering, aiming and tracking) and cognitive (working memory, processing speed, inhibition) tasks. Results The TN group performed significantly worse than controls on the sensorimotor tracking and aiming tasks and across all cognitive measures. Conclusions The data explain why patients ...
Journal of Rehabilitation and Assistive Technologies Engineering, 2017
Introduction Current methods of assessing the outcomes of intracranial aneurysm treatment for ane... more Introduction Current methods of assessing the outcomes of intracranial aneurysm treatment for aneurysmal subarachnoid haemorrhage are relatively insensitive, and thus unlikely to detect subtle deficits. Failures to identify cognitive and motor outcomes of intracranial aneurysm treatment might prevent delivery of optimal post-operative care. There are also concerns over risks associated with using intracranial aneurysm treatment as a preventative measure. Methods We explored whether our kinematic tool would yield useful information regarding motor/cognitive function in patients who underwent intracranial aneurysm treatment for aneurysmal subarachnoid haemorrhage or unruptured aneurysm. Computerised kinematic motor and learning tasks were administered alongside standardised clinical outcome measures of cognition and functional ability, in 10 patients, as a pilot trial. Tests at post-intracranial aneurysm treatment discharge and six-week follow-up were compared to see which measures de...
Disturbance forces facilitate motor learning, but theoretical explanations for this counterintuit... more Disturbance forces facilitate motor learning, but theoretical explanations for this counterintuitive phenomenon are lacking. Smooth arm movements require predictions (inference) about the force-field associated with a workspace. The Free Energy Principle (FEP) suggests that such ‘active inference’ is driven by ‘surprise’. We used these insights to create a formal model that explains why disturbance helps learning. In two experiments, participants undertook a continuous tracking task where they learned how to move their arm in different directions through a novel 3D force field. We compared baseline performance before and after exposure to the novel field to quantify learning. In Experiment 1, the exposure phases (but not the baseline measures) were delivered under three different conditions: (i) robot haptic assistance; (ii) no guidance; (iii) robot haptic disturbance. The disturbance group showed the best learning as our model predicted. Experiment 2 further tested our FEP inspired...
PLOS ONE, 2019
Some activities can be meaningfully dichotomised as 'cognitive' or 'sensorimotor' in naturebut ma... more Some activities can be meaningfully dichotomised as 'cognitive' or 'sensorimotor' in naturebut many cannot. This has radical implications for understanding activity limitation in disability. For example, older adults take longer to learn the serial order of a complex sequence but also exhibit slower, more variable and inaccurate motor performance. So is their impaired skill acquisition a cognitive or motor deficit? We modelled sequence learning as a process involving a limited capacity buffer (working memory), where reduced performance restricts the number of elements that can be stored. To test this model, we examined the relationship between motor performance and sequence learning. Experiment 1 established that older adults were worse at learning the serial order of a complex sequence. Experiment 2 found that participants showed impaired sequence learning when the non-preferred hand was used. Experiment 3 confirmed that serial order learning is impaired when motor demands increase (as the model predicted). These results can be captured by reinforcement learning frameworks which suggest sequence learning will be constrained both by an individual's sensorimotor ability and cognitive capacity.
British Journal of Occupational Therapy, 2017
Introduction Older adults show increased postural sway and a greater risk of falls when completin... more Introduction Older adults show increased postural sway and a greater risk of falls when completing activities with high cognitive demands. While dual-task approaches have clarified an association between cognitive processes and postural control, it is unclear how manual ability, which is also required for the successful completion of cognitively demanding tasks (such as putting a key into a lock), affects this relationship. Method Kinematic technology was used to explore the relationship between postural sway and manual control in healthy younger and older adults. Participants ( n = 82) remained standing to complete a visual-motor tracking task on a tablet computer. Root mean square tracking error measured manual performance, and a balance board measured deviations in centre of pressure as a marker of postural sway. Results Older adults displayed poorer manual accuracy and increased postural sway across all testing conditions. Conclusions Cognitive capacity can interact with multipl...
Geriatrics, 2016
Background: Transcranial Direct Current Stimulation (tDCS) of the primary motor cortex (M1) can m... more Background: Transcranial Direct Current Stimulation (tDCS) of the primary motor cortex (M1) can modulate neuronal activity, and improve performance of basic motor tasks. The possibility that tDCS could assist in rehabilitation (e.g., for paresis post-stroke) offers hope but the evidence base is incomplete, with some behavioural studies reporting no effect of tDCS on complex motor learning. Older adults who show age-related decline in movement and learning (skills which tDCS could potentially facilitate), are also under-represented within tDCS literature. To address these issues, we examined whether tDCS would improve motor sequence learning in healthy young and older adults. Methods: In Experiment One, young participants learned 32 aiming movements using their preferred (right) hand whilst receiving: (i) 30 min Anodal Stimulation of left M1; (ii) 30 min Cathodal Stimulation of right M1; or (iii) 30 min Sham. Experiment Two used a similar task, but with older adults receiving Anodal Stimulation or Sham. Results: Whilst motor learning occurred in all participants, tDCS did not improve the rate or accuracy of motor learning for either age group. Conclusion: Our results suggest that the effects of tDCS may be limited to motor performance with no clear beneficial effects for motor learning.
Beyond Anthropometrics: Prehensile Control Analysis for Capability Assessment
Designing Around People, 2016
How can we design objects that are better suited to people with disabilities? Finite Element Anal... more How can we design objects that are better suited to people with disabilities? Finite Element Analysis is a useful technique for engineering physical objects, but optimal design must be informed by how the human interacts with objects. Our group is attempting to model the control of hand movements in order to create CAD packages that allow object design to be informed by an individual’s sensorimotor control strategies (Prehensile Control Analysis). Prehension, the ability to reach-grasp-and-manipulate objects, is one of the most important human capabilities. Numerous activities of daily living (dressing, feeding, cleaning etc.) rely on dexterity, so it is perhaps unsurprising that impairment of prehension (through illness, injury or ageing decline) is often associated with disability. The kinematics of reach-to-grasp movements show high levels of stereotypicality in neurologically intact adults whilst impairment produces predictable kinematic changes in behaviour. Moreover, kinematics change lawfully as a function of the task and the properties of the object. These facts open up the exciting possibility of modelling prehensile kinematics so that a designer can determine the optimal object properties for an individual with a given impairment. This chapter presents a simple model for characterising an individual’s quality of movement in a given reach-to-grasp movement. Our model is able to capture typical and atypical prehension and is the first step in the development of CAD for handheld objects: a tool that allows design around people.
PloS one, 2016
Attention underpins many activities integral to a child's development. However, methodologica... more Attention underpins many activities integral to a child's development. However, methodological limitations currently make large-scale assessment of children's attentional skill impractical, costly and lacking in ecological validity. Consequently we developed a measure of 'Visual Motor Attention' (VMA)-a construct defined as the ability to sustain and adapt visuomotor behaviour in response to task-relevant visual information. In a series of experiments, we evaluated the capability of our method to measure attentional processes and their contributions in guiding visuomotor behaviour. Experiment 1 established the method's core features (ability to track stimuli moving on a tablet-computer screen with a hand-held stylus) and demonstrated its sensitivity to principled manipulations in adults' attentional load. Experiment 2 standardised a format suitable for use with children and showed construct validity by capturing developmental changes in executive attention pr...
Journal of Surgical Simulation, 2016
Background: In minimally invasive surgery (MIS), the natural relationship between hand and eye is... more Background: In minimally invasive surgery (MIS), the natural relationship between hand and eye is disrupted, i.e. surgeons typically control tools inserted through the patient's abdomen while viewing the workspace on a remote monitor, which can be located in a variety of positions. This separates the location of visual feedback from the area in which a motor action is executed. Previous studies suggest that the visual display should be placed directly ahead of the surgeon (i.e. to preserve visual-motor mapping). However, the extent of the impact of this rotation on surgical performance is unknown. Methods: Eighteen participants completed an aiming task on a tablet PC within a surgical box trainer using a laparoscopic tool in a controlled simulated environment. Visual feedback was presented on a remote monitor located at 0 , AE 45 and AE 90 , with order randomised using the Latin Square method. Results: Movements were significantly slower when the monitor was 90 relative to midline, but spatial accuracy was unaffected by monitor position. Interestingly, the effect of reduced speed in the 90 condition was transient, decreasing over time, suggesting rapid adaptation to the rotation. Conclusions: We conclude that the angle of the visual display in the context of MIS may require a surgeon to adapt to a changed mapping between visual inputs and motor outputs. While this adaptation occurs relatively quickly, it may interfere with skilled actions (e.g. intracorporeal suturing) in complex surgical procedures.
i-Perception, 2012
Handedness, the preference towards using the right or left hand, is established in early childhoo... more Handedness, the preference towards using the right or left hand, is established in early childhood. Such specialisation allows a higher level of motor skill to be maintained in the preferred hand through continuous practice and performance. We might expect that hand asymmetries increase as we age because of the length of time practising with the preferred hand but recent research has suggested reduced asymmetries in older adults performing reaches (Przybla et al 2011, Neurosci Lett, 99-104). To examine whether older adults exhibit asymmetries in a fine visual-motor task, we measured tracing performance along paths of different thickness in a group of young and old participants. Participants completed the task with their preferred (right) and non-preferred (left) hand. We used Movement Time (MT) and Shape Accuracy (SA) as dependant variables. A composite measure of MT and SA, the Speed Accuracy Cost Function (SACF) provided an overall measure of performance efficiency. Younger participants were faster and more accurate than the old, especially when using the preferred hand and/or when task demands were high (ie, tracing thinner paths). Critically we compared performance between right and left hands and revealed reduced asymmetries in MT and SACF in the older group. The young were significantly faster when tracing with their dominant hand, but older participants were equally slow with either hand. Our findings compliment the growing literature which reports decreased hemispheric lateralisation of function in the aging brain (eg, Cabeza 2002, Psychol Aging, 85-100).
Acta neurochirurgica, Jan 2, 2015
Trigeminal neuralgia (TN) is a serious health problem, causing brief, recurrent episodes of stabb... more Trigeminal neuralgia (TN) is a serious health problem, causing brief, recurrent episodes of stabbing or burning facial pain, which patients describe as feeling like an electric shock. The consequences of living with the condition are severe. There is currently no cure for TN and management of the condition can be complex, often delayed by misdiagnosis. Patients' qualitative experiential accounts of TN have not been reported in the literature. Capturing subjective experiences can be used to inform the impact of the condition on quality of life and may contribute to a better understanding of current clinical practice with the aim of improving patient care. Participants with TN (n = 16; 11 female), including those who have and have not undergone surgical intervention(s), took part in one of four focus groups. We conducted a thematic analysis within an essentialist framework using transcripts. The impact of TN and treatment on the lives of participants emerged as four predominant th...
PloS one, 2015
Some studies have shown that manual asymmetries decrease in older age. These results have often b... more Some studies have shown that manual asymmetries decrease in older age. These results have often been explained with reference to models of reduced hemispheric specialisation. An alternative explanation, however, is that hand differences are subtle, and capturing them requires tasks that yield optimal performance with both hands. Whereas the hemispheric specialisation account implies that reduced manual asymmetries should be reliably observed in older adults, the 'measurement difficulty' account suggests that manual asymmetries will be hard to detect unless a task has just the right level of difficulty-i.e. within the 'Goldilocks Zone', where it is not too easy or too hard, but just right. Experiment One tested this hypothesis and found that manual asymmetries were only detected when participants performed in this zone; specifically, performance on a tracing task was only superior in the preferred hand when task constraints were high (i.e. fast speed tracing). Experim...
PLoS ONE, 2012
Reach-to-grasp movements change quantitatively in a lawful (i.e. predictable) manner with changes... more Reach-to-grasp movements change quantitatively in a lawful (i.e. predictable) manner with changes in object properties. We explored whether altering object texture would produce qualitative changes in the form of the precontact movement patterns. Twelve participants reached to lift objects from a tabletop. Nine objects were produced, each with one of three grip surface textures (high-friction, medium-friction and low-friction) and one of three widths (50 mm, 70 mm and 90 mm). Each object was placed at three distances (100 mm, 300 mm and 500 mm), representing a total of 27 trial conditions. We observed two distinct movement patterns across all trials-participants either: (i) brought their arm to a stop, secured the object and lifted it from the tabletop; or (ii) grasped the object 'on-the-fly', so it was secured in the hand while the arm was moving. A majority of grasps were on-the-fly when the texture was high-friction and none when the object was low-friction, with medium-friction producing an intermediate proportion. Previous research has shown that the probability of on-the-fly behaviour is a function of grasp surface accuracy constraints. A finger friction rig was used to calculate the coefficients of friction for the objects and these calculations showed that the area available for a stable grasp (the 'functional grasp surface size') increased with surface friction coefficient. Thus, knowledge of functional grasp surface size is required to predict the probability of observing a given qualitative form of grasping in human prehensile behaviour.
PLoS ONE, 2013
Old age is associated with reduced mobility of the hand. To investigate age related decline when ... more Old age is associated with reduced mobility of the hand. To investigate age related decline when reaching-to-lift an object we used sophisticated kinematic apparatus to record reaches carried out by healthy older and younger participants. Three objects of different widths were placed at three different distances, with objects having either a high or low friction surface (i.e. rough or slippery). Older participants showed quantitative differences to their younger counterparts-movements were slower and peak speed did not scale with object distance. There were also qualitative differences with older adults showing a greater propensity to stop the hand and adjust finger position before lifting objects. The older participants particularly struggled to lift wide slippery objects, apparently due to an inability to manipulate their grasp to provide the level of precision necessary to functionally enclose the object. These data shed light on the nature of age related changes in reaching-to-grasp movements and establish a powerful technique for exploring how different product designs will impact on prehensile behavior.
Neuropsychologia, 2007
Reach-to-grasp (prehension) movements are normally accurate, precise and stereotypical in movemen... more Reach-to-grasp (prehension) movements are normally accurate, precise and stereotypical in movement pattern. These features disappear when haptic feedback is removed in 'virtual reality' systems or when participants pantomime prehension. [Goodale, M. A., Jakobsen, L. S., Keillor, J. M. (1994). Differences in the visual control of pantomimed and natural grasping movements. Neuropsychologia, 32, 1159-1178] suggested that pantomimed reaches are unnatural in form because the ventral rather than the dorsal stream mediates them. We tested whether calibration can prevent 'unnatural' prehension. Calibration refers to the use of an error (visual and/or kinaesthetic) signal to refine performance. We asked participants to reach-and-grasp in four conditions: (A) baseline; (B) reaching-to-grasp with haptic feedback (visual open-loop prehension to a physical object); (C) no feedback (visual-open-loop prehension to an object that could be seen but not felt); (D) a random mixture of (B) and (C). A 45 • mirror was used to display objects without any reduction in visual quality. The normal decrements in performance were observed in condition (C) but not in the identical trials randomly embedded with feedback trials in condition (D). These findings show that participants can produce normal visual-open-loop prehension in the absence of haptic feedback when calibration is allowed. Thus, dorsal stream processing can support pantomimed reaching when calibration is allowed.
Intrinsic scaling of reaches-to-grasp predicted by affordance-based model: Testing men and women with large and small grip spans
Journal of Vision, 2011
Abstract Reaching-to-grasp has been extensively studied to discover the functional timing of the ... more Abstract Reaching-to-grasp has been extensively studied to discover the functional timing of the movements, but, not the spatial scaling relations. However, Mon-Williams and Bingham (2005; submitted) discovered the affordance properties of objects that determine the spatial structure of reach-to-grasp movements. Using these findings, they formulated a model that contained a single free parameter and other variables that were determined by object, maximum object extent (MOE), and actor, maximum grip span (MGS), properties. In this ...
Age differences negotiating paths of different widths at different speeds: does old age mean "middle of the road"?
Journal of Vision, 2011
Abstract Skilled movements deteriorate with increased age for well-documented physiological reaso... more Abstract Skilled movements deteriorate with increased age for well-documented physiological reasons. Reduced sensory sensitivity and biomechanical attenuation can interfere with motor function making older adults more variable in their responses. We examined the degree to which older adults manage to compensate for this increase in visual-motor variability when carrying out two skilled actions: tracing and steering. In both cases, participants generated trajectories within the boundaries of a delineated path. When ...
Does better performance mean better learning in visuomotor tasks?
Journal of Vision, 2013
Reaching with feeling
Journal of Vision, 2004
Abstract Skilled movement requires the coordination of perception variables and action variables ... more Abstract Skilled movement requires the coordination of perception variables and action variables in respect to their absolute scale and number. The issue of how these variables are transformed in order to close the loop between perception and action is fundamental to our understanding of skilled behaviour. We manipulated the physical properties (location and size) of a visually constant object in order to explore the role of somatosensory feedback information in the calibration of visual information for action. All participants (n= 60) were ...
Uploads
Papers by Mark Mon-Williams