The control of object manipulation tasks involves the close interplay of predictive and reactive control mechanisms. For example, when lifting an object, people typically predict the weight based on object size and material as well as sensorimotor memory obtained from previous lifts of the object. When lifting objects with a precision grip, people increase vertical load force to a target level that slightly exceeds the predicted weight. When the object is heavier than expected, the mismatch between expected and actual tactile signals associated with lift-off triggers a corrective action within ~100 ms, that involves probing increases in load force that continue until the object is lifted. Here we investigated whether this correction action can be adaptively influenced by experience. Participants repeatedly lifted an object that was instrumented with force sensors to measure the forces applied by the fingertips, with weight that could be varied without the knowledge of the participant. In 80% of trials, the weight was set to 2 N and, in different blocks of 110 trials, the remaining 20 % of trials (2 trials randomly selected from each successive 10 trials) was set to either 4 or 6 N. We found that the rate of change of the reflexively triggered increase in load force that occurred in the 4 or 6 N trials, scaled with the additional weight. That is, following the initial increase in load force to ~2 N, the subsequent increase in load force was more rapid for the 6 N object than the 4 N object. In contrast, the onset time of the reactive increase in load force was independent of the additional weight. Finally, this adaptation of reactive load force control took place quickly and was evident after only a few lifts of the heavier weight. These results indicate that the reactive increases in load force that occur when a lifted object is heavier than expected can be adapted and tuned, to refine behavior. This further suggests that multiple predictions can be generated about object weight when lifting. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2013-02-02 13:34:20.533

Healthy aging influences peripheral and central levels of the neuromotor system. These age-related changes contribute to the decline in dexterous manual behavior. Difficulty in performing activities of daily living increases reliance on external assistance. Understanding specific mechanisms leading to the decline in fine manual performance is crucial for their rehabilitation. In this thesis, we have attempted to increase our awareness of the causes underlying manual disability in old age. The first study investigated how old adults apply forces and moments on a freely-movable object using a precision grip (thumb and index finger) during functionally-relevant tasks. During the grasp-lift task old adults misaligned their thumb and finger contacts and produced greater grip force, greater external moments on the object around its roll axis, and oriented force vectors differently compared with young adults. During a precision-orientation task of inserting a slot on the object over a bar (`key-slot' task), old adults were more variable in digit-tip force directions and performed the key-slot task more slowly. With practice old adults aligned their digits, reduced their grip force, and minimized external moments on the object. We conclude that with old age comes with a reduced ability to control the forces and moments applied to objects during precision grasp and manipulation. This may contribute to the ubiquitous slowing and deteriorating manual dexterity in healthy aging. Another study investigated the effects of transcranial direct current stimulation (tDCS) to the contralateral M1 combined with motor training (MP) on changes in the forces applied to the object during grasp and manipulation. We also measured performances on functional tasks in healthy elderly individuals. Our results indicate that anodal tDCS+MP facilitates retention of learning on a skillful manual task in healthy old adults. Furthermore, improved retention on the pegboard test was associated with reduced force variability on the key-slot task that demanded similar precise control over the forces applied to the object. These findings suggest that the improvement in force steadiness is one of the potential mechanisms through which short-term anodal tDCS during motor training improved performance on a functional task that outlasted the intervention period. Furthermore, anodal tDCS over M1 in combination with motor practice also influenced motor response to tasks that critically depend on sensory signals in healthy old adults. Finally, we found that, in healthy elderly individuals, the memory representations scaling the lift force for the grip and lift task generalized, while the training-based learning on the ballistic task showed an incomplete transfer to the contralateral hand. These differences may indicate task-dependent interhemispheric transfer of learning in old age. Collectively, the work presented in this thesis demonstrates that the performance on dexterous manual tasks in healthy old adults may depend on how they configure their grasp, and control their finger forces (both linear and rotational) applied to the grasped object, specifically how smooth is the applied force.

The primary purpose of this study was to observe the relationship between muscle activation of the right hand with the force produced at the fingertips in an isometric precision pinch tracking task. Thirty right-handed subjects, 15 males and 15 females, with a mean age 23.5 (SD 3.5) years, free from any neurological disorder or physical ailment, had a pair of electromyography (EMG) electrodes placed over the first dorsal interosseous (FDI) muscle, which acts on the index finger, while performing a pinch force tracking task scaled to 20% maximum voluntary contraction (MVC). The tracking task was chosen because it created a continuously increasing force application to 20% MVC and then decreasing force release from 20% MVC at a prescribed rate in both cases of 6.66% MVC force per second. In addition to showing increases in EMG activation of the FDI with increases in force, the results revealed that muscle activation for a given force level was generally greater for force application than for force release. This may be due dynamics of muscle contraction or to patterns of multiple muscle coordination. / text

The reactive control of fingertip forces maintaining grasp stability was examined in man during a prehensile task. Blindfolded subjects used the precision grip between the tips of index finger and thumb to restrain an object that was subjected to unpredictable load forces. These were delivered tangential to the parallel grip surfaces of the object. Load forces, grip forces (perpendicular to the grip surfaces) and position of the object were recorded.Subjects automatically adjusted the grip forces to loads of various amplitudes and rates. Thereby they maintained a reliable safety margin against frictional slips without using excessive grip forces. A rapid rise in grip force lasting about 0.2 s was triggered after a short delay following the onset of a sustained ramp load increase. This 'catch-up' response caused a quick restoration of an adequate grip:load force ratio that prevented frictional slips. If the ramp load continued to increase after the catchup response, the grip force also increased in parallel with the load change in a 'tracking' manner. Consequently, during the hold phases of 'ramp-and-hold' loads, the employed grip forces were approximately proportional to the load amplitude. Sensory information about the rate of change of the load force parametrically scaled the 'catchup' and 'tracking' responses.Following anesthetic block of sensory input from the digits, the grip responses were both delayed and attenuated or even abolished. To compensate for these impairments, subjects had to voluntarily maintain exceedingly high grip forces to prevent the object from slipping. The grip control improved slightly during hand and forearm support conditions that allowed marked wrist movements to occur in response to the loading. This indicates that signals from receptors in muscles, joints or skin areas proximal to the digits can to some extent be used to adjust grip forces during impaired digital sensibility. In contrast, these signals had only minor influence on the control during normal digital sensibility.Grip responses to loads delivered in various directions revealed that the load direction, in relation to gravity and to the hand's geometry, represents intrinsic task variables in the automatic processes that maintain a stable grasp. The load direction influenced both the response latencies and the magnitudes of the grip responses. The response latencies were shortest for loads in directions that were the most critical with regard to the consequences of frictional slippage, i.e., loads directed away from the palm or in the direction of gravity. Recordings of signals in cutaneous afferents innervating the finger tips demonstrated that these effects on the response latencies depended on differences in the time needed by the central nervous system to implement the motor responses. The short latencies in the most ‘criticar load directions may reflect the preparation of a default response, while additional central processing would be needed to execute the response to loads in other directions. Adjustments to local frictional anisotropies at the digit-object interface largely explained the magnitude effects.In conclusion, grip responses are automatically adjusted to the current loading condition during unpredictable loading of a hand held object. Subjects call up a previously acquired sensorimotor transform that supports grasp stability by preventing both object slippage and excessive grip forces. Cutaneous sensory information about tangential forces and frictional conditions at the digit-object interface is used to initiate and scale the grip responses to the current loading conditions, largely in a predictive manner. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1995, Härtill 5 uppsatser</p> / digitalisering@umu

Les mouvements sont le résultat de contractions musculaires dont l’organisation spatio-temporelle est régie par des structures cérébrales et médullaires. Etudier les circuits qui les sous-tendent est une étape indispensable pour renforcer nos connaissances des mécanismes à l’origine de la commande des mouvements volontaires et pour mieux comprendre la pathophysiologie des mouvements anormaux. Les muscles squelettiques sont innervés par les motoneurones alpha de la moelle épinière qui à leur out sont influencés par des neurones des aires corticales motrices. Cette voie descendante constitue la voie corticomotoneuronale (CM) et est responsable de l’exécution des mouvements volontaires. Le cortex moteur primaire est considéré comme une structure clé, au cœur du système, permettant l’intégration complexe de nombreuses influences multi-régions pour conduire aux comportements moteurs adéquats. Les interactions qui existent entre les différents groupes de neurones au sein de M1 influent en dernier lieu sur la sortie motrice. De la balance complexe entre ces influences inhibitrices et excitatrices, locales ou à distance va dépendre l’état d’excitabilité des cellules CM contrôlant les différents muscles. L'objectif de ce travail de thèse était d'étudier comment évoluent certains de ces mécanismes excitateurs ou inhibiteurs du cortex moteur primaire lorsque la commande motrice volontaire d’un muscle de l’index est modifiée. Nous avons étudié le rôle de ces mécanismes dans les changements d’excitabilité de la voie CM qui accompagnent la contraction tonique volontaire du muscle premier interosseus dorsalis (FDI) en comparant une tâche simple mais peu naturelle : l’abduction de l'index, une tâche naturelle plus complexe: la pince pouce-index et la condition de repos musculaire. Nous avons également étudié l’effet de la commande motrice sur l’interaction entre deux de ces mécanismes inhibiteurs l’un à longue latence, la LICI, l’autre à courte latence, la SICI. Enfin nous avons souhaité évaluer le décours temporel de ces mécanismes dans un cadre pathologique tâche-dépendant: la crampe de l’écrivain. Pour cela, nous avons utilisé la technique d’electromyographie de surface pour enregistrer les potentiels moteurs évoqués par la Stimulation Magnétique Transcrânienne. Nous avons mis en évidence une modulation tâche-dépendante de la LICI. Par rapport à la tâche d’abduction simple, la LICI s’estompait plus tôt lors de la tâche de pince pouce-index, traduisant une désinhibition plus précoce lors d’un mouvement plus complexe. Nous avons observé, et ce pour la première fois dans la littérature, une phase de facilitation nette qui suivait cette désinhibition, et qui était absente lorsque le muscle était au repos. Ces résultats sont également visibles dans un muscle voisin du FDI, non engagé dans la tâche; cela suggère que les mécanismes à l’origine de la facilitation sont impliqués dans l’activité volontaire sans spécificité topographique. L’interaction entre la LICI et la SICI n’a pas été modifiée par la tâche effectuée, laissant penser qu’elle n’est pas impliquée dans les changements d’excitabilité tâche-dépendants. Enfin, il apparaît que la désinhibition est retardée chez les sujets dystoniques quand le muscle est engagé dans un mouvement complexe de pince pouce-index mais pas dans une tâche simple d’abduction de l’index en comparaison à des sujets contrôles. Ces résultats illustrent le fait que lors d’un mouvement plus complexe, l’efficacité des circuits inhibiteurs du cortex moteur primaire est modifiée, ce qui permet de réguler l’activité des cellules CM, afin d’adapter la commande motrice au mouvement souhaité. Le fait que cette désinhibition soit retardée dans une tâche complexe (proche de la tâche affectée) mais pas dans une tâche simple chez les patients atteints d’une crampe de l’écrivain suggère que les mécanismes à l’origine de la désinhibition pourraient participer aux troubles moteurs qui caractérisent la maladie. / Movements are evoked by muscles contractions whose spatial organization is mediated by both spinal and cortical components. It is important to investigate the underlying circuitry of movements to extend our knowledge on how voluntary movement are controlled and to better understand the pathophysiology of movements disorders. The spinal alpha motoneurons innervating distal muscles are controlled at least in parts by corticomotoneuronal neurons located in the motor cortical areas. Among them, the primary motor cortex is considered as a key structure, performing a complex integration of multi-regional influences leading to appropriate motor behaviors. Axons from corticomotoneuronal (CM) cells of the primary motor cortex reach the spinal cord via descending motor pathway. CM neurons are influenced by local or distant, inhibitory and excitatory components which determine the balance of excitability. The aim of this thesis was to explore changes of some of the excitatory and inhibitory mechanisms of motor cortex as a function of the task being performed. We assessed the time course of Long-interval Intracortical Inhibition (LICI), Late Cortical Disinhibition (LCD) and Long interval Intracortical Facilitation (LICF), which are mechanisms that potentially act to modulate the output of CM controlling the first dorsal interosseus (FDI) muscle. We compared three conditions : index finger abduction (a simple but not natural task), precision grip between index and thumb ( amore natural and complex task), and rest. We also evaluated the effect of task on interaction between LICI and Short Interval Intracortical Inhibition (SICI). Finally, we assessed the time course of LICI in patients suffering from writer’s cramp. For this purpose, we used surface electromyography to record motor potentials evoked by Transcranial Magnetic Stimulation.We showed a task-dependent change in late inhibitory and disinhibitory components. Compared with abduction task, the LICI induced during precision grip was shorter, suggesting an early disinhibition in more complex task. The disinhibition was followed by a period of facilitation only during the active tasks, i.e. facilitation was not observed when all muscles were at restat rest. However, long interval intracortical facilitation can be observed in a muscle at rest not engaged in an active task if a neighboring muscle is activated. It is therefore likely that mechanisms underlying facilitation are associated with voluntary contraction albeit with lack of topographic specificity. Interaction between LICI and SICI was not modified between tasks, suggesting that it was not involved in task-dependent changes of cortical excitability. Lastly, disinhibition was shown to be delayed in dystonic patients when the FDI was actively engaged in a precision grip but not in index abduction, compared with control subjects. An explanation might be that mechanisms underlying disinhibition are impaired in thumb-index precision grip (a task similar to that inducing unwanted contractions in writer’s cramp). Task-specidic disruption of LICI and late cortical disinhibition may therefore be at least in part responsible for pathophysiology of dystonia. It is likely that during complex task, the efficacy of LICI, and more generally of motor cortex inhibitory mechanisms, is modified to allow adaptation of CM neurons activity to the functional requirements of the motor task being performed.

During dexterous manipulation with the fingertips, forces are applied to objects' surfaces. To achieve grasp stability, these forces must be appropriate given the properties of the objects and the skin of the fingertips, and the nature of the task. It has been demonstrated that tactile sensors in the fingertips provide crucial information about both object properties and mechanical events critical for the control of fingertip forces, while in certain tasks vision may also contribute to predictions of required fingertip actions. This thesis focuses on two specific aspects of the sensory control of manipulation: (i) how individual fingers are controlled for grasp stability when people restrain objects subjected to unpredictable forces tangential to the grasped surfaces, and (ii) how tactile sensors in the fingertips encode direction of fingertip forces and shape of surfaces contacted by the fingertips. When restraining objects with two fingers, subjects adjust the fingertip forces to the local friction at each digit-object interface for grasp stability. This is accomplished primarily by partitioning the tangential force between the digits in a way that reflects the local friction whereas the normal forces at the involved digits are scaled by the average friction and the total load. The neural control mechanisms in this task rely on tactile information pertaining to both the friction at each digit-object interface and the development of tangential load. Moreover, these mechanisms controlled the force application at individual digits while at the same time integrating sensory inputs from all digits involved in the task. Microneurographical recordings in awake humans shows that most SA-I, SA-II and FA-I sensors in the distal phalanx are excited when forces similar to those observed during actual manipulation are applied to the fingertip. Moreover, the direction of the fingertip force influences the impulse rates in most afferents and their responses are broadly tuned to a preferred direction. The preferred direction varies among the afferents and, accordingly, ensembles of afferents can encode the direction of fingertip forces. The local curvature of the object in contact with the fingertip also influenced the impulse rates in most afferents, providing a curvature contrast signals within the afferent populations. Marked interactions were observed in the afferents' responses to object curvature and force direction. Similar findings were obtained for the onset latency in individual afferents. Accordingly, for ensembles of afferents, the order by which individual afferents initially discharge to fingertip events effectively represents parameters of fingertip stimulation. This neural code probably represents the fastest possible code for transmission of parameters of fingertip stimuli to the CNS.

Le contrôle moteur fin et précis des doigts est une habileté importante dans la vie quotidienne pour écrire ou manger par exemple. Ce contrôle moteur est pris en charge par le cortex moteur primaire (M1) qui transmet le signal neuronal à la moelle épinière via la voie corticospinale. Le macaque rhésus est un excellent modèle pour étudier ce système moteur car, comme chez l’humain, il possède cette voie cortico-motoneuronale directe. Bien que les déficits du contrôle moteur de la main suite à des inactivations de M1 aient été étudiés sur des modèles de singes, peu d’études ont décrit les changements musculaires sous-tendant ces déficits. Le but de cette étude était d’évaluer les effets d’une inactivation partielle de M1 sur le comportement et l’activation du patron musculaire du membre supérieur chez le macaque rhésus. Pour ce faire, nous avons effectué des injections intra-corticales de Muscimol, un agoniste du GABA, pour inactiver temporairement l’aire de représentation de la main de M1. Des singes ont été entrainés à réaliser une tâche d’atteinte et de préhension qui requière l’utilisation du pouce et de l’index pour attraper une pastille de nourriture. En parallèle, les activités électromyographiques (EMG) des muscles proximaux et distaux du membre supérieur contralatéral aux sites d’injections ont été enregistrées. L’inactivation partielle de M1 entraine différents déficits moteurs comme une diminution du taux de succès, une perte des mouvements indépendants des doigts, une première flexion de l’index plus lente, et l’apparition de nouvelles stratégies de préhension pour attraper la pastille. Dans le cas de trouble sévère, les singes ont présentés tous ces déficits comportementaux. Ces troubles moteurs étaient sous-tendus par des activités musculaires anormales. En effet, les analyses EMG ont mis en évidence des changements dans les latences et les patrons d’activations musculaires des muscles proximaux et distaux au cours de la phase d’atteinte, d’ajustement et de préhension. Dans le cas de trouble modéré, les patrons d’activations musculaires étaient préservés malgré certain déficits visibles. Cependant, les patrons d’activations musculaires étaient altérés si la tâche demandait une rotation de l’avant-bras et de la main. Ces résultats montrent que les déficits comportementaux et les changements musculaires dépendent de la sévérité des troubles moteurs et/ou de la difficulté de la tâche (i.e. une rotation de l’avant-bras). / Fine digit movements contribute to many different aspects of our daily life and require appropriate muscle coordination. The main pathway through which M1 sends motor commands to spinal motor neurons is via the corticospinal tract. The rhesus macaque, like humans, have this direct corticomotoneuronal pathway of M1, making it a useful model to study this system. Although the effect of M1 inactivation on the control of the hand in term of behavioral changes has been studied in monkeys, little is known of how muscle activation patterns of the upper limb during reaching and grasping in monkeys becomes altered. The goal of this study was to evaluate the effect of a partial inactivation of the primary motor cortex (M1) in rhesus macaques on both behavioral performance and muscle activations. To do so we performed intra-cortical injections of Muscimol, a GABA agonist, to inactivate the hand area of M1. Monkeys performed a reach-to-grasp task that required a precision grip to retrieve a food pellet from a well. Electromyographic (EMG) activity of the proximal and distal muscles of the contralateral upper limb were recorded and quantified relative to the behavioral performance. We found that depending on the severity of the impairment, the Muscimol injection could induce several different movement abnormalities, such as decrease in the success rate, loss of independent finger movements, longer duration of the first flexion of the index finger, and use of alternate types of grasp to retrieve the food pellet. In cases of severe impairment, monkeys displayed all these movement abnormalities concurrently. In addition, we observed that behavioral deficits were associated with muscle discoordination. Indeed, EMG analysis revealed that the latencies and the muscle activation patterns were altered during the reach, hand preshaping and the grasp phases of the movement. These inappropriate EMG activities were visible on both proximal and distal muscles of the upper limb. In cases of mild impairment, monkeys had fewer behavioral deficits, but still showed some changes in the temporal muscle activation patterns. In contrast to the severe cases, the muscle activation patterns were more preserved. Interestingly, in the mild cases, the muscle activation patterns were altered if a rotation of the forearm was required by the task. Thus, we found that behavioral and muscular activation changes were dependent on the severity of the impairment and/or the difficulty of the task (i.e. required a rotation of the forearm).

La dextérité, notamment la pince de précision (i.e., opposition pouce-index) est une fonction très développée chez l’homme. Elle est basée sur l’habileté à contrôler précisément et indépendamment les forces et mouvements des doigts en relation avec les contraintes de la tâche. Les muscles de la main responsables du mouvement des doigts sont gouvernés par le système corticospinal (CS) latéral. La principale source de ce système CS est l’aire motrice primaire (M1), laquelle possède des projections CS directes sur les motoneurones des muscles de la main. Cependant, d’autres projections CS en provenance des aires motrices non primaires ont été trouvées, notamment en provenance de l’aire motrice supplémentaire (SMA). Chez l’homme, la fonctionnalité de cette voie dans le contrôle habile des doigts a peu été étudiée. L’objectif de cette thèse est d’étudier, chez l’homme, l’implication des projections CS de la SMA lors de contrôle manuel précis de force. Pour ce faire, nous avons utilisé la stimulation magnétique transcrânienne (TMS) et l’électroencéphalographie (EEG).A travers différentes études, nous avons pu mettre en évidence l’importante implication de la SMA dans la dextérité. Il semblerait que cette aire puisse agir en parallèle à M1 en régulant directement l’excitabilité des motoneurones de la moelle épinière. En conclusion, nos résultats suggèrent que M1 et SMAp ont une influence directe et efficace sur la production de force pendant des tâches motrices manuelles fines. / Human dexterity is a highly developed function based on the ability to independently and precisely control forces and movements of the fingers related to the constraints of the task. Hand muscles for finger movements are steered by the lateral corticospinal (CS) system. The main source of this CS system is the primary motor area (M1), which has direct CS projections on motoneurons innervating hand muscles. Recently, CS projections from non-primary motor area have also been found, especially from the supplementary motor area (SMA). However, the functionality of this CS tract in human manual force control is little studied. The aim of this thesis was to study the implication of the CS projections from SMA in precision manual force control, using electroencephalography (EEG) and transcranial magnetic stimulation (TMS).Altogether, the results obtained in our different studies show the important implication of SMA in dexterity. It appears that this area can act in parallel with M1, directly influencing excitability of spinal motoneurons. We conclude that M1 and SMA both have direct and efficient influence on force production during fine manual motor tasks.

Le pouce opposable de la main joue un rôle essentiel dans le comportement humain, permettant une prise bien plus précise que celle des singes avec les pouces opposables. Comment le cerveau contrôle t-il les mains aussi précisément? Dans le cadre de cette thèse, nous avons étudié comment différentes régions du cerveau dédiées au contrôle moteur, en particulier le cortex moteur (M1) et l’aire motrice supplémentaire (AMS), contribuent à une pince pouce-index précise. Les résultats de nos études révèlent que des neurones dans l’AMS, en complément de ceux dans M1, communiquent directement avec les motoneurones de la moelle épinière contrôlant les muscles de la main. De plus, SMA communique aussi efficacement que M1 avec les muscles de la main, alors que chez le singe, celle avec M1 est plus efficace. Cette différence fonctionnelle dans la voie AMS-muscles entre le singe et l’Homme pourrait expliquer la plus grande capacité de ce dernier à contrôler finement la force produite par les doigts. / The human hand's opposable thumb plays a large role in human behavior, allowing for a grip far more precise than that of monkeys with opposable thumbs. However, it isn't well understood how the brain controls the hands in such a precise way. In these studies, we investigate how different parts of the brain dedicated to motor tasks, in particular the motor cortex (M1) and the supplementary motor area (SMA), contribute to a precise thumb-index finger grip. Our experiments suggest that some neurons in the SMA, in addition to those well-described in M1, may connect directly to the motoneurons in the spinal cord controlling the hand muscles. Moreover, we found that SMA communicates with the hand muscles as efficiently as M1, while in monkeys, SMA communicates less efficiently than M1. This functional difference in the SMA-muscles pathway between monkey and human may account for the higher capacity of the latter to precisely control the force produced by digits.

A wide literature of predominantly behavioural experiments that use Stimulus Response Compatibility (SRC) have suggested that visual action information such as object affordance yields rapid and concurrent activation of visual and motor brain areas, but has rarely provided direct evidence for this proposition. This thesis examines some of the key claims from the affordance literature by applying electrophysiological measures to well established SRC procedures to determine the verities of the behavioural claims of rapid and automatic visuomotor activation evoked by viewing affording objects. The temporal sensitivity offered by the Lateralised Readiness Potential and by visual evoked potentials P1 and N1 made ideal candidates to assess the behavioural claims of rapid visuomotor activation by seen objects by examining the timecourse of neural activation elicited by viewing affording objects under various conditions. The experimental work in this thesis broadly confirms the claims of the behavioural literature however it also found a series of novel results that are not predicted by the behavioural literature due to limitations in reaction time measures. For example, while different classes of affordance have been shown to exert the same behavioural facilitation, electrophysiological measures reveal very different patterns of cortical activation for grip-type and lateralised affordances. These novel findings question the applicability of the label ‘visuomotor’ to grip-type affordance processing and suggest considerable revision to models of affordance. This thesis also offers a series of novel and surprising insights into the ability to dissociate afforded motor activity from behavioural output, into the relationship between affordance and early visual evoked potentials, and into affordance in the absence of the intention to act. Overall, this thesis provides detailed suggestions for considerable changes to current models of the neural activity underpinning object affordance.