5 research outputs found
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Post-stroke object affordances: An EEG investigation
Rehabilitating upper limb function after stroke is a key therapeutic goal. In healthy brains, objects, especially tools, are said to cause automatic motoric âaffordancesâ; affecting our preparation to handle objects. For example, the N2 event-related potential has been shown to correlate with the functional properties of objects in healthy adults during passive viewing. We posited that such an affordance effect might also be observed in chronicstage stroke survivors. With either dominant or non-dominant hand forward, we presented three kinds of stimuli in stereoscopic depth; grasp objects affording a power-grip, pinch objects affording a thumb and forefinger precision-grip and an empty desk, affording no action. EEG data from 10 stroke survivors and 15 neurologically healthy subjects were analysed for the N1 and N2 ERP components. Both components revealed differences between the two object stimuli categories and the empty desk for both groups, suggesting the presence of affordance-related motor priming from around 100 to 370 ms after stimulus onset. Hence, we speculate that stroke survivors with loss of upper limb function may benefit from object presentation regimes designed to maximise motor priming when attempting movements with manipulable objects. However, further investigation would be necessary with acute stage patients, especially those diagnosed with apraxia
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The temporal nature of affordance: an investigation using EEG and TMS
Affordances play a part in how we prepare to handle objects. Tools and other manipulable objects are said to automatically âaffordâ various actions depending upon the motor repertoire of the actor. Evidence obtained through behavioural experiments, fMRI, EEG and TMS has proven that this is the case but, as yet, the temporal evolution of affordances has not been fully investigated. Determining the critical time-scale may have significance to patients with brain damage or motor disorders when attempting object manipulation. There are many other factors involved in therapy but it is worth considering that there could be an optimum period of time to view an object before the benefit of an automatic affordance is no longer available. In a series of experiments using the novel approach of positioning the participantâs dominant hand closer to or further from the object being viewed, together with use of three dimensional stimuli, and through application of behavioural assays, TMS pulses and EEG recordings, this research examined temporal properties of affordances in young healthy control subjects. Verification of this motoric activity by EEG led to investigating chronic phase stroke survivors with remaining upper limb deficits and comparing their brain activity with age-matched control participants. As EEG and TMS both have good temporal properties, they are ideal converging methodologies for this kind of investigation. By mapping how affordances develop and dissipate, this work has yielded pure scientific advances in the field of motor decision making. Further, it has resulted in suggestions for future research relating to a possible method to improve rehabilitation interventions for patients who are neurologically impaired by stroke
How the brain grasps tools: fMRI & motion-capture investigations
Humansâ ability to learn about and use tools is considered a defining feature of our species, with most related neuroimaging investigations involving proxy 2D picture viewing tasks. Using a novel tool grasping paradigm across three experiments, participants grasped 3D-printed tools (e.g., a knife) in ways that were considered to be typical (i.e., by the handle) or atypical (i.e., by the blade) for subsequent use. As a control, participants also performed grasps in corresponding directions on a series of 3D-printed non-tool objects, matched for properties including elongation and object size. Project 1 paired a powerful fMRI block-design with visual localiser Region of Interest (ROI) and searchlight Multivoxel Pattern Analysis (MVPA) approaches. Most remarkably, ROI MVPA revealed that hand-selective, but not anatomically overlapping tool-selective, areas of the left Lateral Occipital Temporal Cortex and Intraparietal Sulcus represented the typicality of tool grasping. Searchlight MVPA found similar evidence within left anterior temporal cortex as well as right parietal and temporal areas. Project 2 measured hand kinematics using motion-capture during a highly similar procedure, finding hallmark grip scaling effects despite the unnatural task demands. Further, slower movements were observed when grasping tools, relative to non-tools, with grip scaling also being poorer for atypical tool, compared to non-tool, grasping. Project 3 used a slow-event related fMRI design to investigate whether representations of typicality were detectable during motor planning, but MVPA was largely unsuccessful, presumably due to a lack of statistical power. Taken together, the representations of typicality identified within areas of the ventral and dorsal, but not ventro-dorsal, pathways have implications for specific predictions made by leading theories about the neural regions supporting human tool-use, including dual visual stream theory and the two-action systems model