Pointing to remembered visual targets after active one-step self-displacements within reaching space. 1999

W P Medendorp, and S Van Asselt, and C C Gielen
Department of Medical Physics and Biophysics, University of Nijmegen, The Netherlands. pieter@mbfys.kun.nl

We studied pointing movements to remembered visual targets in a completely darkened room with and without self-made step movements in order to investigate in which coordinate system and to what extent target representations relative to the body are updated for self-induced egomotion. A small red-light-emitting diode on the fingertip provided visual feedback about fingertip position at all times. We asked subjects to make pointing movements that started 2 s after disappearance of a visual target. In this interval of 2 s the subject did or did not make a step. The pointing errors without a step showed that subjects undershot faraway targets in a systematic way, whereas they sometimes overshot nearby targets. We found that the step causes larger pointing errors both in amplitude and direction with a bias in the direction of the step. We explored three different versions of a descriptive model in which polar coordinates were used to describe the pointing movement, and in which either Cartesian or polar coordinates were used to update target position relative to the shoulder for the step. The results suggest that incorporation of the step displacement in the new target position relative to the subject is done in a Cartesian frame of reference. Moreover, the amplitude of the step displacement tends to be underestimated by subjects.

UI MeSH Term Description Entries
D008297 Male Males
D008568 Memory Complex mental function having four distinct phases: (1) memorizing or learning, (2) retention, (3) recall, and (4) recognition. Clinically, it is usually subdivided into immediate, recent, and remote memory.
D008875 Middle Aged An adult aged 45 - 64 years. Middle Age
D009068 Movement The act, process, or result of passing from one place or position to another. It differs from LOCOMOTION in that locomotion is restricted to the passing of the whole body from one place to another, while movement encompasses both locomotion but also a change of the position of the whole body or any of its parts. Movement may be used with reference to humans, vertebrate and invertebrate animals, and microorganisms. Differentiate also from MOTOR ACTIVITY, movement associated with behavior. Movements
D010775 Photic Stimulation Investigative technique commonly used during ELECTROENCEPHALOGRAPHY in which a series of bright light flashes or visual patterns are used to elicit brain activity. Stimulation, Photic,Visual Stimulation,Photic Stimulations,Stimulation, Visual,Stimulations, Photic,Stimulations, Visual,Visual Stimulations
D011597 Psychomotor Performance The coordination of a sensory or ideational (cognitive) process and a motor activity. Perceptual Motor Performance,Sensory Motor Performance,Visual Motor Coordination,Coordination, Visual Motor,Coordinations, Visual Motor,Motor Coordination, Visual,Motor Coordinations, Visual,Motor Performance, Perceptual,Motor Performance, Sensory,Motor Performances, Perceptual,Motor Performances, Sensory,Perceptual Motor Performances,Performance, Perceptual Motor,Performance, Psychomotor,Performance, Sensory Motor,Performances, Perceptual Motor,Performances, Psychomotor,Performances, Sensory Motor,Psychomotor Performances,Sensory Motor Performances,Visual Motor Coordinations
D005260 Female Females
D005385 Fingers Four or five slender jointed digits in humans and primates, attached to each HAND. Finger
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000328 Adult A person having attained full growth or maturity. Adults are of 19 through 44 years of age. For a person between 19 and 24 years of age, YOUNG ADULT is available. Adults

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