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Previous studies have attempted to map somatosensory space via haptic matching tasks and have shown that individuals make large and systematic matching errors, the magnitude and angular direction of which vary systematically through the workspace. Based upon such demonstrations, it has been suggested that haptic space is non-Euclidian. This conclusion(More)
Within the medial frontal cortex, the supplementary eye field (SEF), supplementary motor area (SMA), and pre-SMA have been implicated in the control of voluntary action, especially during motor sequences or tasks involving rapid choices between competing response plans. However, the precise roles of these areas remain controversial. Here, we study two(More)
The role of visual information and the precise nature of the representations used in the control of prehension movements has frequently been studied by having subjects reach for target objects in the absence of visual information. Such manipulations have often been described as preventing visual feedback; however, they also impose a working memory load not(More)
Theories of attention have frequently pointed to the finding that there is a significant performance decrement ('cost') to responding to two different objects concurrently. However, much of the research aimed at investigating how attention is 'divided' in such circumstances has adopted response time (RT) as the measure of interest. In this paper we(More)
Several common neuropsychiatric disorders (e.g., obsessive-compulsive disorder, Tourette syndrome (TS), autistic spectrum disorder) are associated with unpleasant bodily sensations that are perceived as an urge for action. Similarly, many of our everyday behaviors are also characterized by bodily sensations that we experience as urges for action. Where do(More)
This paper presents evidence in support of a serial reaction time (SRT) deficit associated with Parkinson's disease, and related to the acquisition or execution of serial-order information. Eleven patients with idiopathic Parkinson's disease, and 10 age-matched but otherwise healthy control subjects, were compared on a variant of the SRT task introduced by(More)
Contextual cues such as linear perspective and relative size can exert a powerful effect on the perception of objects. This fact is demonstrated by the illusory effects that can be induced by such cues (e.g., the Ponzo railway track and Titchener circles illusions). Several recent studies have reported, however, that visual illusions based on such cues have(More)
Ensuring that behavior remains appropriate over time requires dynamic, flexible control. We used the task-switching procedure to investigate the mechanisms whereby advance information is used to control behavior under conditions of frequently changing task-rules. The color of target stimuli signaled which task-set (or behavioral 'rule') was required on each(More)
The posterior parietal cortex (PPC) is thought to play an important role in the sensorimotor transformations associated with reaching movements. In humans, damage to the PPC, particularly bilateral lesions, leads to impairments of visually guided reaching movements (optic ataxia). Recent accounts of optic ataxia based upon electrophysiological recordings in(More)
It has been proposed that patients with spatial neglect fail to respond appropriately toward stimuli opposite their brain lesion because they have an impairment of directing attention. However, a disorder of 'intention' - or movement initiation - has also been demonstrated in this condition. Recently, the paths of neglect patients' reaches have been shown(More)