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Reference systems for coding spatial information in normal subjects and a deafferented patient

โœ Scribed by J. Blouin; C. Bard; N. Teasdale; J. Paillard; M. Fleury; R. Forget; Y. Lamarre


Book ID
104673051
Publisher
Springer-Verlag
Year
1993
Tongue
English
Weight
857 KB
Volume
93
Category
Article
ISSN
0014-4819

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โœฆ Synopsis


To produce accurate goal-directed arm movements, subjects must determine the precise location of target object. Position of extracorporeal objects can be determined using: (a) an egocentric frame of reference, in which the target is localized in relation to the position of the body; and/or (b) an allocentric system, in which target position is determined in relation to stable visual landmarks surrounding the target (Bridgeman 1989; Paillard 1991). The present experiment was based on the premise that (a) the presence of a structured visual environment enables the use of an allocentric frame of reference, and (b) the sole presence of a visual target within a homogeneous background forces the registration of the target location by an egocentric system. Normal subjects and a deafferented patient (i.e., with an impaired egocentric system) pointed to visual targets presented in both visual environments to evaluate the efficiency of the two reference systems. For normals, the visual environment conditions did not affect pointing accuracy. However, kinematic parameters were affected by the presence or absence of a structured visual surrounding. For the deafferented patient, the presence of a structured visual environment permitted a decrease in spatial errors when compared with the unstructured surrounding condition (for movements with or without visual feedback of the trajectory). Overall, results support the existence of an egocentric and an allocentric reference system capable of organizing extracorporeal space during arm movements directed toward visual targets.


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The relative contribution of retinal and
โœ Jean Blouin; Gabriel M. Gauthier; Jean-Louis Vercher; Jonathan Cole ๐Ÿ“‚ Article ๐Ÿ“… 1996 ๐Ÿ› Springer-Verlag ๐ŸŒ English โš– 568 KB

This experiment investigated the relative extent to which different signals from the visuo-oculomotor system are used to improve accuracy of arm movements. Different visuo-oculomotor conditions were used to produce various retinal and extraretinal signals leading to a similar target amplitude: (a) f