Impairments in action and perception after right intraparietal damage.

We examined visually-guided reaching and perception in an individual who underwent resection of a small tumor in right intraparietal sulcus (pIPS). In the first experiment, she reached to targets presented on a touch screen. Vision was occluded from reach onset on half of the trials, whereas on the other half she had vision during the entire reach.

Movement Imitation via an Abstract Trajectory Representation in Dorsal Premotor Cortex.

Humans are particularly good at copying novel and meaningless gestures. The mechanistic and anatomical basis for this specialized imitation ability remains largely unknown. One idea is that imitation occurs by matching body configurations.

The mirror illusion's effects on body state estimation.

The mirror illusion uses a standard mirror to create a compelling illusion in which movements of one limb seem to be made by the other hidden limb. In this paper we adapt a motor control framework to examine which estimates of the body's configuration are affected by the illusion. We propose that the illusion primarily alters estimates related to upcoming states of the body (the desired state and the predicted state), with smaller effects on the estimate of the body state prior to movement initiation.

Corrigendum: The role of action representations in thematic object relations.

[This corrects the article on p. 140 in vol. 8, PMID: 24672461.

Enhancing the mirror illusion with transcranial direct current stimulation.

Visual feedback has a strong impact on upper-extremity movement production. One compelling example of this phenomena is the mirror illusion (MI), which has been used as a treatment for post-stroke movement deficits (mirror therapy). Previous research indicates that the MI increases primary motor cortex excitability, and this change in excitability is strongly correlated with the mirror's effects on behavioral performance of neurologically-intact controls.

Effects of vibrotactile feedback on human learning of arm motions.

Tactile cues generated from lightweight, wearable actuators can help users learn new motions by providing immediate feedback on when and how to correct their movements. We present a vibrotactile motion guidance system that measures arm motions and provides vibration feedback when the user deviates from a desired trajectory. A study was conducted to test the effects of vibrotactile guidance on a subject's ability to learn arm motions.

The role of action representations in thematic object relations.

A number of studies have explored the role of associative/event-based (thematic) and categorical (taxonomic) relations in the organization of object representations. Recent evidence suggests that thematic information may be particularly important in determining relationships between manipulable artifacts. However, although sensorimotor information is on many accounts an important component of manipulable artifact representations, little is known about the role that action may play during the processing of semantic relationships (particularly thematic relationships) between multiple objects.

Response interference between functional and structural object-related actions is increased in patients with ideomotor apraxia.

We report data from two left hemisphere stroke patients with moderate-to-severe ideomotor apraxia who exhibited deficits in positioning their hands to use 'conflict' objects (objects grasped and used with different hand postures) relative to controls and patients with mild apraxia. These novel data support the claim that actions to common objects are subject to interference between multiple responses, and suggest that errors in apraxia may be attributed to deficient resolution of competition between appropriate and inappropriate actions.

Visuo-motor gain adaptation and generalization following left hemisphere stroke.

During gain adaptation, participants must learn to adapt to novel visuo-motor mappings in which the movement amplitudes they produce do not match the visual feedback they receive. The aim of the present study was to investigate the neural substrates of gain adaptation by examining its possible disruption following left hemisphere stroke. Thirteen chronic left hemisphere stroke patients and five healthy right-handed control subjects completed three experimental phases involving reaching with the left hand, which was the less-affected hand in patients.

Extending Fitts' Law to three-dimensional obstacle-avoidance movements: support for the posture-based motion planning model.

According to Fitts' Law, the time (MT) to move to a target is a linear function of the logarithm of the ratio between the target's distance and width. Although Fitts' Law accurately predicts MTs for direct movements, it does not accurately predict MTs for indirect movements, as when an obstacle intrudes on the direct movement path. To address this limitation, Jax et al.

Contributions of efference copy to limb localization: evidence from deafferentation.

Previous research with deafferented subjects suggests that efference copy can be used to update limb position. However, the contributions of efference copy to limb localization are currently unclear. We examined the performance of JDY, a woman with severe, longstanding proprioceptive deficits from a sensory peripheral neuropathy, on a reaching task to explore the contribution of efference copy to trajectory control.

Response interference between functional and structural actions linked to the same familiar object.

Viewing objects with the intention to act upon them may activate task-irrelevant motor responses. Many manufactured objects are associated with two action classes: grasping in accordance with object structure and skillful use consistent with object function. We studied the potential for within-object competition during action selection by comparing initiation latencies for "conflict" objects (with competing structure and function responses) to "non-conflict" objects (with a single response).

The posture-based motion planning framework: new findings related to object manipulation, moving around obstacles, moving in three spatial dimensions, and haptic tracking.

We describe the results of recent studies inspired by the posture-based motion planning theory (Rosenbaum et al., 2001). The research concerns analyses of human object manipulation, obstacle avoidance, three-dimensional movement generation, and haptic tracking, the findings of which are discussed in relation to whether they support or fail to support the premises of the theory.

Disorders of the perceptual-motor system.

The study of patients with movement disorders provides insight into both the functional organization and the neural substrates of the perceptual-motor system. By and large, we feel this source of information has been underutilized within the basic science of motor control. To begin to address this shortcoming, this chapter reviews three disorders of the perceptual-motor system (disorders of the body schema, optic ataxia, and ideomotor apraxia) and illustrates how the study of these disorders can inform central issues within the field of motor control.

Two-component models of reaching: evidence from deafferentation in a Fitts' law task.

Both feedforward and feedback mechanisms are used to ensure accurate movements. Feedback information comes primarily from vision and proprioception; the relative contributions of these modalities to on-line control of action and internal model maintenance remain unclear. We report data from an experiment in which a chronically deafferented subject (JDY) and nine controls were asked to reach to targets of different sizes both with and without vision.

Toward an integrated account of object and action selection: a computational analysis and empirical findings from reaching-to-grasp and tool-use.

The act of reaching for and acting upon an object involves two forms of selection: selection of the object as a target, and selection of the action to be performed. While these two forms of selection are logically dissociable, and are evidently subserved by separable neural pathways, they must also be closely coordinated. We examine the nature of this coordination by developing and analyzing a computational model of object and action selection first proposed by Ward [Ward, R.

More than (where the target) meets the eyes: disrupted visuomotor transformations in optic ataxia.

Visually guided reaching entails multiple coordinate frame transformations between retina-centered target location and body-centered limb location. Reaching errors in optic ataxia (OA) may be caused by disruptions to these transformations. Consistent with this proposal, previous studies report that reaching errors in OA depend primarily on the location of a target relative to the patient's gaze regardless of its location relative to the head or body midline.

Hand path priming in manual obstacle avoidance: rapid decay of dorsal stream information.

The dorsal, action-related, visual stream has been thought to have little or no memory. This hypothesis has seemed credible because functions related to the dorsal stream have been generally unsusceptible to priming from previous experience. Tests of this claim have yielded inconsistent results, however.

Hand path priming in manual obstacle avoidance: evidence for abstract spatiotemporal forms in human motor control.

Previous research suggests that motor equivalence is achieved through reliance on effector-independent spatiotemporal forms. Here the authors report a series of experiments investigating the role of such forms in the production of movement sequences. Participants were asked to complete series of arm movements in time with a metronome and, on some trials, with an obstacle between 1 or more of the target pairs.

The problem of serial order in behavior: Lashley's legacy.

In a prescient paper Karl Lashley (1951) rejected reflex chaining accounts of the sequencing of behavior and argued instead for a more cognitive account in which behavioral sequences are typically controlled with central plans. An important feature of such plans, according to Lashley, is that they are hierarchical. Lashley offered several sources of evidence for the hierarchical organization for behavioral plans, and others afterward provided more evidence for this hypothesis.

Extending Fitts' Law to manual obstacle avoidance.

In this study we asked whether Fitts' Law, a well-established relationship that predicts movement times (MTs) for direct movements between two positions, could be extended to predict MTs for curved, obstacle avoiding, movements. We had participants make movements in the presence of an obstacle. Using these data, we tested an extensions of Fitts' Law that predicted MTs based on the movement's index of difficulty and the distance that the obstacle intruded into the direct movement path.

Hand path priming in manual obstacle avoidance: evidence that the dorsal stream does not only control visually guided actions in real time.

According to a prominent theory of human perception and performance (M. A. Goodale & A.

Deficits in movement planning and intrinsic coordinate control in ideomotor apraxia.

Two central issues in the field of motor control are the coordinate frame in which movements are controlled and the distinction between movement planning and online correction. In this study we used these issues to frame several hypotheses about the deficits underlying ideomotor apraxia (IMA). In particular, we examined whether ideomotor apraxics exhibited (1) deficits in movement control in intrinsic (body relative) coordinates with better control in extrinsic (workspace relative) coordinates, (2) deficits in movement planning that are compensated for by an overreliance on online correction, or (3) both deficits.

Computational motor control and human factors: modeling movements in real and possible environments.

An aim of human factors research is to have models that allow for the advance design of user-friendly environments. This is still a distant dream because existing models are not yet sufficiently sophisticated. Models in the domain of motor control are a case in point, but recent developments in computational motor control suggest that the gap between the current state of modeling in this area and the desired state is shrinking.