Biomedical subjects

Stephen R Jackson

Publications and source records attributed to Stephen R Jackson.

3 recordsLinked to original sources

PubMed2002

Noninformative vision improves haptic spatial perception.

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 assumes that spatial perception is modality specific, and it largely ignores the fact that tactile matching tasks involve active, exploratory arm movements. Here we demonstrate that, when individuals match two bar stimuli (i.e., make them parallel) in circumstances favoring extrinsic (visual) coordinates, providing noninformative visual information significantly increases the accuracy of haptic perception. In contrast, when individuals match the same bar stimuli in circumstances favoring the coding of movements in intrinsic (limb-based) coordinates, providing identical noninformative visual information either has no effect or leads to the decreased accuracy of haptic perception. These results are consistent with optimal integration models of sensory integration in which the weighting given to visual and somatosensory signals depends upon the precision of the visual and somatosensory information and provide important evidence for the task-dependent integration of visual and somatosensory signals during the construction of a representation of peripersonal space.

Functional Laterality↗

PubMed2002

Visual attention in blindsight: sensitivity in the blind field increased by targets in the sighted field.

Damage to primary visual cortex results in a scotoma, or region of blindness, which can nevertheless be accompanied by residual visual abilities in the affected field. This dissociation of visual processing and visual experience is often described as blindsight. We investigated the role of visual attention in blindsight and the application of limited visual resources between the blind and sighted fields in a well-studied case. Contrary to expectations based on normal capacity limits, processing a target in the sighted field improved rather than interfered with processing of targets in the blind field. The benefit from the sighted field was greater when blind and sighted targets were in symmetric locations about the vertical meridian.

Adult↗

PubMed2002

Monocular vision leads to a dissociation between grip force and grip aperture scaling during reach-to-grasp movements.

It has been argued that visual perception and the visual control of action depend upon functionally distinct and anatomically separable brain systems. Electrophysiological evidence indicates that binocular vision may be particularly important for the visuomotor processing within the posterior parietal cortex, and neuropsychological and psychophysical studies confirm that binocular vision is crucial for the accurate planning and control of prehension movements. An unresolved issue concerns the consequences for visuomotor processing of removing binocular vision. By one account, monocular viewing leads to reliance upon pictorial visual cues to calibrate grasping and results in disruption to normal size-constancy mechanisms. This proposal is based on the finding that maximum grip apertures are reduced with monocular vision. By a second account, monocular viewing results in the loss of binocular visual cues and leads to strategic changes in visuomotor processing by way of altered safety margins. This proposal is based on the finding that maximum grip apertures are increased with monocular vision. We measured both grip aperture and grip force during prehension movements executed with binocular and monocular viewing. We demonstrate that each of the above accounts may be correct and can be observed within the same task. Specifically, we show that, while grip apertures increase with monocular vision, consistent with altered visuomotor safety margins, maximum grip force is nevertheless reduced, consistent with a misperception of object size. These results are related to differences in visual processing required for calibrating grip aperture and grip force during reaching.

Adaptation, Physiological↗