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The development of visual acuity in preterm infants
209
pathway and the limbo-diencephalic system
may allow the l a t e r recoqnition of
spatial locations through the storage of t h e i r representations in parietal cortex. According to t h i s a n a l y s i s , memory of the p a r t i c u l a r locations occupied by p a r t i c u l a r objects would require the association of t h e i r separately stored representations in parietal and temporal c o r t i c e s , respectively. Evidence w i l l be presented i n d i c a t i n g that one structure which may mediate such associations is the hippocampal formation.
THE DEVELOPMENTOF VISUAL ACUITY IN PRETERM INFANTS MOHN, G.*, VAN HOF-VAN DUIN, J . * , FETTER, W.P.F.**, METTAU, J.W.** AND BAERTS, W.** * Dept. of Physiology I , Erasmus U n i v e r s i t e i t Rotterdam, P.O.Box 1738, Rotterdam, The Netherlands **Sophiakinderziekenhuis, Gordelweg, Rotterdam, The Netherlands The development of visual a c u i t y in normal, f u l l - t e r m i n f a n t s has been studied e x t e n s i v e l y over the l a s t years. The present study addressed the question of whether the extra visual experience or prematurely born infants a f f e c t s a c u i t y development. Previous studies suggest that t h i s is not the case, but precise a c u i t y measurements of preterm infants have not been made. Visual a c u i t y was assessed by means of the p r e f e r e n t i a l - l o o k i n g technique. Gratings of d i f f e r e n t s t r i p e widths, each paired with a blank f i e l d of equal luminance, were presented to the i n f a n t , while an observer who was unaware of the l e f t / r i g h t
position of the grating stimulus was required to judge the s t i -
mulus position on the basis of the i n f a n t ' s reaction. Acuity was then taken as the f i n e s t s t r i p e width f o r which the observer performed with s i g n i f i c a n t accuracy. Up t i l l
now, 35 a c u i t y estimates have been obtained in 28 i n f a n t s born 4-14
weeks prematurely, and ranging in age from 11 to 59 weeks from b i r t h .
In these
i n f a n t s , a c u i t y was c o n s i s t e n t l y lower than that of normal f u l l - t e r m i n f a n t s of comparable postnatal age. However, when ages were corrected f o r prematurity, i . e . calculated from the date at which t h e i n f a n t s
should normally have been
born a f t e r 40 weeks g e s t a t i o n , a c u i t y values of f u l l - t e r m and preterm i n f a n t s overlapped, i n d i c a t i n g that visual experience p r i o r to the normal gestational age at b i r t h does indeed not influence a c u i t y development.
210
Acuity in the preterm i n f a n t s did not show any evident r e l a t i o n s h i p to subependymal haemorrhage or minor v e n t r i c u l a r d i l a t a t i o n s as indicated by u l t r a sound scans. Two infants with i n t r a v e n t r i c u l a r as well as subependymal haemorrhage had low visual a c u i t i e s ; one of these also shows clear neurological abn o r m a l i t i e s . A greater number of infants w i l l be tested to f u r t h e r examine the r e l a t i o n between ultrasound f i n d i n g s and visual a c u i t y .
THREE DIMENSIONAL TRAJECTORIES OF THE ARM MORASSO, P. I s t i t u t o di E l e t t r o t e c n i c a , Universit~ di Genova, Nucleo di Bioingegneria e Robotica Antromorfa, C.N.R., Genova, I t a l y Arm t r a j e c t o r i e s have been studied p r e v a l e n t l y for planar movements and one of the most robust results which has been observed is the c h a r a c t e r i s t i c segmentation of the hand v e l o c i t y p r o f i l e and the coupling between shape and speed of the t r a j e c t o r i e s .
For planar t r a j e c t o r i e s ,
the notion of shape is captured
by the behaviour of curvature along a t r a j e c t o r y : a marked bend involves a peak in the curvature p r o f i l e , a s t r a i g h t course causes the curvature to go to zero, and i n f l e c t i o n points are characterized by a zero-crossing of the curvature profile. For spatial t r a j e c t o r i e s ,
in addition to express the way in which the t r a -
j e c t o r y is "bent", we need an additional information which expresses the " t w i s t ing" of the t r a j e c t o r y ,
i . e . the way in which the local ( " o s c u l a t i n g " ) plane of
the t r a j e c t o r y changes i t s o r i e n t a t i o n . This information is conveyed by the profile
of t o r s i o n . Therefore, in 3-D space the notion of t r a j e c t o r y shape can be
conveniently expressed by the curvature and the torsion p r o f i l e s . A question which can be addressed is whether the coupling between shape and speed observed in 2-D s t i l l
holds in 3-D. This question was investigated experi-
mentally by recording 3-D movements, p a r t i c u l a r l y 3-D s c r i b b l e s , and the answer suggested by the experimental data is that the "bending" of the t r a j e c t o r y is coupled with speed, whereas the " t w i s t i n g " is independent of speed. The implications of these f i n d i n g s are interpreted in the framework of a computational model of t r a j e c t o r y formation I previously investigated f o r planar movements. The basic features of the planar model are preserved and the model is extended to the 3-D case in a straigh~forwarded way. The behaviour of the model, tested by means of s i m u l a t i o n , is congruent with the experimental r e s u l t s , with p a r t i c u l a r regard to the d i s s o c i a t i o n between "bending" and " t w i s t i n g " .
pathway and the limbo-diencephalic system
may allow the l a t e r recoqnition of
spatial locations through the storage of t h e i r representations in parietal cortex. According to t h i s a n a l y s i s , memory of the p a r t i c u l a r locations occupied by p a r t i c u l a r objects would require the association of t h e i r separately stored representations in parietal and temporal c o r t i c e s , respectively. Evidence w i l l be presented i n d i c a t i n g that one structure which may mediate such associations is the hippocampal formation.
THE DEVELOPMENTOF VISUAL ACUITY IN PRETERM INFANTS MOHN, G.*, VAN HOF-VAN DUIN, J . * , FETTER, W.P.F.**, METTAU, J.W.** AND BAERTS, W.** * Dept. of Physiology I , Erasmus U n i v e r s i t e i t Rotterdam, P.O.Box 1738, Rotterdam, The Netherlands **Sophiakinderziekenhuis, Gordelweg, Rotterdam, The Netherlands The development of visual a c u i t y in normal, f u l l - t e r m i n f a n t s has been studied e x t e n s i v e l y over the l a s t years. The present study addressed the question of whether the extra visual experience or prematurely born infants a f f e c t s a c u i t y development. Previous studies suggest that t h i s is not the case, but precise a c u i t y measurements of preterm infants have not been made. Visual a c u i t y was assessed by means of the p r e f e r e n t i a l - l o o k i n g technique. Gratings of d i f f e r e n t s t r i p e widths, each paired with a blank f i e l d of equal luminance, were presented to the i n f a n t , while an observer who was unaware of the l e f t / r i g h t
position of the grating stimulus was required to judge the s t i -
mulus position on the basis of the i n f a n t ' s reaction. Acuity was then taken as the f i n e s t s t r i p e width f o r which the observer performed with s i g n i f i c a n t accuracy. Up t i l l
now, 35 a c u i t y estimates have been obtained in 28 i n f a n t s born 4-14
weeks prematurely, and ranging in age from 11 to 59 weeks from b i r t h .
In these
i n f a n t s , a c u i t y was c o n s i s t e n t l y lower than that of normal f u l l - t e r m i n f a n t s of comparable postnatal age. However, when ages were corrected f o r prematurity, i . e . calculated from the date at which t h e i n f a n t s
should normally have been
born a f t e r 40 weeks g e s t a t i o n , a c u i t y values of f u l l - t e r m and preterm i n f a n t s overlapped, i n d i c a t i n g that visual experience p r i o r to the normal gestational age at b i r t h does indeed not influence a c u i t y development.
210
Acuity in the preterm i n f a n t s did not show any evident r e l a t i o n s h i p to subependymal haemorrhage or minor v e n t r i c u l a r d i l a t a t i o n s as indicated by u l t r a sound scans. Two infants with i n t r a v e n t r i c u l a r as well as subependymal haemorrhage had low visual a c u i t i e s ; one of these also shows clear neurological abn o r m a l i t i e s . A greater number of infants w i l l be tested to f u r t h e r examine the r e l a t i o n between ultrasound f i n d i n g s and visual a c u i t y .
THREE DIMENSIONAL TRAJECTORIES OF THE ARM MORASSO, P. I s t i t u t o di E l e t t r o t e c n i c a , Universit~ di Genova, Nucleo di Bioingegneria e Robotica Antromorfa, C.N.R., Genova, I t a l y Arm t r a j e c t o r i e s have been studied p r e v a l e n t l y for planar movements and one of the most robust results which has been observed is the c h a r a c t e r i s t i c segmentation of the hand v e l o c i t y p r o f i l e and the coupling between shape and speed of the t r a j e c t o r i e s .
For planar t r a j e c t o r i e s ,
the notion of shape is captured
by the behaviour of curvature along a t r a j e c t o r y : a marked bend involves a peak in the curvature p r o f i l e , a s t r a i g h t course causes the curvature to go to zero, and i n f l e c t i o n points are characterized by a zero-crossing of the curvature profile. For spatial t r a j e c t o r i e s ,
in addition to express the way in which the t r a -
j e c t o r y is "bent", we need an additional information which expresses the " t w i s t ing" of the t r a j e c t o r y ,
i . e . the way in which the local ( " o s c u l a t i n g " ) plane of
the t r a j e c t o r y changes i t s o r i e n t a t i o n . This information is conveyed by the profile
of t o r s i o n . Therefore, in 3-D space the notion of t r a j e c t o r y shape can be
conveniently expressed by the curvature and the torsion p r o f i l e s . A question which can be addressed is whether the coupling between shape and speed observed in 2-D s t i l l
holds in 3-D. This question was investigated experi-
mentally by recording 3-D movements, p a r t i c u l a r l y 3-D s c r i b b l e s , and the answer suggested by the experimental data is that the "bending" of the t r a j e c t o r y is coupled with speed, whereas the " t w i s t i n g " is independent of speed. The implications of these f i n d i n g s are interpreted in the framework of a computational model of t r a j e c t o r y formation I previously investigated f o r planar movements. The basic features of the planar model are preserved and the model is extended to the 3-D case in a straigh~forwarded way. The behaviour of the model, tested by means of s i m u l a t i o n , is congruent with the experimental r e s u l t s , with p a r t i c u l a r regard to the d i s s o c i a t i o n between "bending" and " t w i s t i n g " .