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“Here” and “there” as determinants of visually guided gestures. Some evidence in normal and brain damaged subjects
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"HERE" AND "THERE" AS DETERMINANTSOF VISUALLY GUIDED GESTURES. SOMEEVIDENCE IN NORMAL AND BRAIN DAMAGEDSUBJECTS BROUCHON, M., JOANETTE, Y. AND PONCET, M. Laboratoire de Neuropsychologie Humaine, E.H.E.S.S., La Vieille-Charit~, 13002 Marseille et D~partement de Neuropsychologie, CHU-La Timone 13005 Marseille, France During the last decade a better understanding of the mechanisms underlying v i s u a l l y guided movements has occured. I t gave rise to a descriptive model which assumes a clearly defined sequential organization: a f i r s t phase corresponding to the limb's transport to the object, completed by a second phase corresponding to the object manipulation. The f i r s t phase can i t s e l f be viewed as comprising two sequential components: f i r s t ,
(a) a pre-programmed projection of the arm to-
wards the object which is achieved through a feedforward system activating peripheralvision, followed by (b) a f i n a l adjustment permitting the hand to make contact with the object, which is achieved through a feedbackward mechanism guided by central vision. In this work, i t is assumed that, given i n t e g r i t y of the previously referred to mechanisms involved in v i s u a l l y guided movements, there s t i l l can be d i f f e r ences in visuo-motor behavior according to the sector of space - or " f i e l d " in which the stimulus is located. For instance, in "normal" subjects, the preprogrammed component of the f i r s t phase - corresponding to the arm projection towards the target - provides different systematic errors i f the target is located in the "prehension" rather than the "locomotory" f i e l d , even i f i t is realized through similar movements. Such a distinction between "prehension" and "Iocomotory" f i e l d s becomes even more drastic in brain-damaged subjects with parietal lesions. When submitted to a task of manual pointing at targets located in the "prehension" f i e l d , they show major impairments of the movements' temporo-spatial
coordinates. On the contrary, the pointing performances of the
same brain-damaged subjects, in a similar task, remain unaffected i f targets are located in the locomotory f i e l d . These facts suggest that two similar movements can be executed in reference to different central representations of space Thus, the ultimate goal of a v i s u a l l y guided movement - reaching in prehension f i e l d versus indicating in locomotory f i e l d - could determine the gesture by itself.
"HERE" AND "THERE" AS DETERMINANTSOF VISUALLY GUIDED GESTURES. SOMEEVIDENCE IN NORMAL AND BRAIN DAMAGEDSUBJECTS BROUCHON, M., JOANETTE, Y. AND PONCET, M. Laboratoire de Neuropsychologie Humaine, E.H.E.S.S., La Vieille-Charit~, 13002 Marseille et D~partement de Neuropsychologie, CHU-La Timone 13005 Marseille, France During the last decade a better understanding of the mechanisms underlying v i s u a l l y guided movements has occured. I t gave rise to a descriptive model which assumes a clearly defined sequential organization: a f i r s t phase corresponding to the limb's transport to the object, completed by a second phase corresponding to the object manipulation. The f i r s t phase can i t s e l f be viewed as comprising two sequential components: f i r s t ,
(a) a pre-programmed projection of the arm to-
wards the object which is achieved through a feedforward system activating peripheralvision, followed by (b) a f i n a l adjustment permitting the hand to make contact with the object, which is achieved through a feedbackward mechanism guided by central vision. In this work, i t is assumed that, given i n t e g r i t y of the previously referred to mechanisms involved in v i s u a l l y guided movements, there s t i l l can be d i f f e r ences in visuo-motor behavior according to the sector of space - or " f i e l d " in which the stimulus is located. For instance, in "normal" subjects, the preprogrammed component of the f i r s t phase - corresponding to the arm projection towards the target - provides different systematic errors i f the target is located in the "prehension" rather than the "locomotory" f i e l d , even i f i t is realized through similar movements. Such a distinction between "prehension" and "Iocomotory" f i e l d s becomes even more drastic in brain-damaged subjects with parietal lesions. When submitted to a task of manual pointing at targets located in the "prehension" f i e l d , they show major impairments of the movements' temporo-spatial
coordinates. On the contrary, the pointing performances of the
same brain-damaged subjects, in a similar task, remain unaffected i f targets are located in the locomotory f i e l d . These facts suggest that two similar movements can be executed in reference to different central representations of space Thus, the ultimate goal of a v i s u a l l y guided movement - reaching in prehension f i e l d versus indicating in locomotory f i e l d - could determine the gesture by itself.