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BACKGROUND When we reach out to pick up an object, not only do we direct our moving limb towards the location of the object, but the opening between our fingers and thumb is scaled in flight to the object's size. Evidence obtained from patients with neurological disorders has shown that the visual processing underlying the calibration of grip aperture and(More)
Although both reaching and grasping require transporting the hand to the object location, only grasping also requires processing of object shape, size and orientation to preshape the hand. Behavioural and neuropsychological evidence suggests that the object processing required for grasping relies on different neural substrates from those mediating object(More)
In humans, functional imaging studies have demonstrated a homologue of the macaque motion complex, MT+ [suggested to contain both middle temporal (MT) and medial superior temporal (MST)], in the ascending limb of the inferior temporal sulcus. In the macaque monkey, motion-sensitive areas MT and MST are adjacent in the superior temporal sulcus.(More)
Previous studies have shown that the BOLD functional MRI (fMRI) signal is increased in several cortical areas when subjects perform anti-saccades compared with pro-saccades. It remains unknown, however, whether this increase is due to an increased cortical motor signal for anti-saccades or due to differences in preparatory set between pro- and anti-saccade(More)
Previous functional imaging studies have shown an increased hemodynamic signal in several cortical areas when subjects perform memory-guided saccades than that when they perform visually guided saccades using blocked trial designs. It is unknown, however, whether this difference results from sensory processes associated with stimulus presentation, from(More)
Posterior parietal cortex (PPC) participates in the planning of visuospatial behaviors, including reach movements, in gaze-centered coordinates. It is not known if these representations encode the visual goal in retinal coordinates, or the movement direction relative to gaze. Here, by dissociating the intrinsic retinal stimulus from the extrinsic direction(More)
Using functional magnetic resonance imaging, we examined the signal in parietal regions that were selectively activated during delayed pointing to flashed visual targets and determined whether this signal was dependent on the fixation position of the eyes. Delayed pointing activated a bilateral parietal area in the intraparietal sulcus (rIPS),(More)
An anti-saccade, which is a saccade directed toward a mirror-symmetrical position in the opposite visual field relative to the visual stimulus, involves at least three separate operations: covert orienting, response suppression, and coordinate transformation. The distinction between pro- and anti-saccades can also be applied to pointing. We used fMRI to(More)
A simple visual test was used to measure how much Listing's plane rotates as a function of the vergence angle. This test measured the elevation-dependent torsional disparity of horizontal and vertical lines during three tasks: vergence on a near target, vergence through prisms that remained fixed, and through prisms that rotated with eye elevation.(More)
We examined the 2D surface formed by 3D eye positions of normal subjects to determine whether the shape and thickness changed in tasks that differed in saccadic directions: random, horizontal, vertical, radial, clockwise and counter-clockwise. Eye positions during the random task did not lie precisely on Listing's plane but on a surface with a small twist.(More)