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The planning of visually guided reaches is accomplished by independent specification of extent and direction. We investigated whether this separation of extent and direction planning for well practiced movements could be explained by differences in the adaptation to extent and directional errors during motor learning. We compared the time course and(More)
Psychophysical studies of reaching movements suggest that hand kinematics are learned from errors in extent and direction in an extrinsic coordinate system, whereas dynamics are learned from proprioceptive errors in an intrinsic coordinate system. We examined consolidation and interference to determine if these two forms of learning were independent.(More)
The paradigm task A-->task B-->task A, which varies the time interval between task A and task B, has been used extensively to investigate the consolidation of motor memory. Consolidation is defined as resistance to retrograde interference (interference by task B on initial learning of task A). Consolidation has been demonstrated for simple skills, motor(More)
This study examined the variability in movement end points in a task in which human subjects reached to targets in different locations on a horizontal surface. The primary purpose was to determine whether patterns in the variable errors would reveal the nature and origin of the coordinate system in which the movements were planned. Six subjects moved a(More)
This study examines the source of direction-dependent errors in movement extent made by human subjects in a reaching task. As in the preceding study, subjects were to move a cursor on a digitizing tablet to targets displayed on a computer monitor. Movements were made without concurrent visual feedback of cursor position, but movement paths were displayed on(More)
The purpose of this study is to examine the mechanisms underlying control of intersegmental dynamics during reaching movements. Two experiments were conducted to determine the relative contributions of anticipatory and somatosensory feedback mechanisms in controlling intersegmental dynamics and whether adaptation to novel intersegmental dynamics generalizes(More)
 We have previously demonstrated that, in preparing themselves to aim voluntary impulses of isometric elbow force to unpredictable targets, subjects selected default values for amplitude and direction according the range of targets that they expected. Once a specific target appeared, subjects specified amplitude and direction through parallel processes.(More)
1. We recently showed that patients lacking proprioceptive input from their limbs have particular difficulty performing multijoint movements. In a pantomimed slicing gesture requiring sharp reversals in hand path direction, patients showed large hand path distortions at movement reversals because of failure to coordinate the timing of the separate reversals(More)
In this review, we describe how pharmacological inactivation can be used to elucidate the central control of skilled limb movement. Local anesthetics and tetrodotoxin block neuronal cell bodies and passing fibers while gamma-aminobutyric acid (GABA) and muscimol only block cell bodies. Blockade induction time is short (several minutes) for all the agents.(More)
1. The dependence of directional biases in reaching movements on the initial position of the hand was studied in normal human subjects moving their unseen hand on a horizontal digitizing tablet to visual targets displayed on a vertical computer screen. 2. When initial hand positions were to the right of midline, movements were systematically biased(More)