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Spectral response curve of visual neurons in the monkey frontal eye field
S184 SPECTRAL
RESPONSE
MASAO AZUMA*, Sch. of Med.,
CURVE
YOSIHIRO Hirosaki
OF V I S U A L
NEURONS
S A S A K I * and 036, J a p a n
HISAO
IN THE M O N K E Y
SUZUKI,
Dept.
FRONTAL
EYE FIELD.
Physiol.,
Hirosaki
Univ.
The v i s u a l n e u r o n s in the m o n k e y f r o n t a l eye f i e l d r e s p o n d e d to a s t i m u l u s a p p e a r i n g in a r e s t r i c t e d p a r t (the r e c e p t i v e field) of the c o n t r a l a t e r a l h e m i field. F u r t h e r m o r e , t h e y w e r e o r g a n i z e d so as to r e p r e s e n t the a r e a f r o m the c e n t r a l to the p e r i p h e r a l v i s u a l f i e l d a c c o r d i n g to t h e i r l o c a t i o n in the c o r t i c a l area. The p u r p o s e of the p r e s e n t e x p e r i m e n t s is to i n v e s t i g a t e the s c o t o p i c a n d / o r p h o t o p i c p r o c e s s r e s p o n s i b l e for g e n e r a t i n g the v i s u a l r e s p o n s e of the neurons. We e x a m i n e d s p e c t r a l r e s p o n s e c h a r a c t e r i s t i c s of the n e u r o n s in the a w a k e m o n k e y u n d e r b o t h d a r k - and l i g h t - a d a p t e d s t a t e s . W h i l e the a n i m a l g a z e d at a small and d i m c e n t e r l i g h t spot, we p r e s e n t e d the s e c o n d l i g h t spot, 0.6 ° in d i a m e t e r for 1 s at the m o s t r e s p o n s i v e site in the v i s u a l f i e l d for e a c h n e u r o n , and e x a m i n e d its r e s p o n s e s . The s p o t w a s a m o n o c h r o m a t i c one r a n g i n g f r o m 400 to 700 nm in w a v e - l e n g t h in 2 0 - n m s t e p s of e q u a l e n e r g y . The i n t e n s i t y of the l i g h t w a s d e c r e a s e d by 0.2 l o g - u n i t s t e p s by n e u t r a l d e n s i t y f i l t e r u n t i l the t h r e s h o l d of the n e u r o n a l r e s p o n s e for e a c h w a v e - l e n g t h w a s d e t e r m i n e d , thus o b t a i n i n g the spectral threshold curve. In the l i g h t - a d a p t e d state, the v i s u a l n e u r o n r e s p o n d e d to e v e r y w a v e - l e n g t h m o n o c h r o m a t i c l i g h t of s t r o n g i n t e n s i t y . W h e n the i n t e n s i t y w a s d e c r e a s e d , the r a n g e of w a v e - l e n g t h for r e s p o n d i n g b e c a m e n a r r o w u n t i l no r e s p o n s e w a s o b t a i n e d at a b o u t a 1 log u n i t d e c r e a s e . W i t h this p r o c e d u r e , we o b t a i n e d s p e c t r a l t h r e s h o l d c u r v e s of a V s h a p e w i t h the l o w e s t t h r e s h o l d at a b o u t 560 nm. In the d a r k - a d a p t e d state, the t h r e s h o l d s w e r e at m o r e 3 log u n i t s and the c u r v e s w e r e s h i f t e d t o w a r d the d i r e c t i o n of s h o r t e r w a v e - l e n g t h (the Purkinje shift). The l o w e s t t h r e s h o l d w a s at 5 0 0 - 5 2 0 nm. It was c o n c l u d e d t h a t in s u c h h i g h e r v i s u a l c e n t e r s , b o t h p h o t o p i c a n d s c o t o p i c p r o c e s s e s c o n v e r g e to e a c h n e u r o n , m a k i n g a s p e c t r a l t h r e s h o l d c u r v e s i m i l a r to t h o s e of h u m a n v i s i o n .
RESPONSE MONKEY
TO
THE
AKICHIKA MIKAMI, Kyoto University,
ALTERNATING
RANDOM
DOT
STIMULI
Department of N e u r o p h y s i o l o g y , I n u y a m a , A i c h i 484, J a p a n
IN
THE
MT
Primate
NEURONS
Research
OF
MACAQUE
Institute,
The m i d d l e t e m p o r a l v i s u a l a r e a (MT) is an e x t r a s t r i a t e v i s u a l a r e a s that is selectively i n v o l v e d in the c o r t i c a l a n a l y s i s of v i s u a l m o t i o n . R e c e n t behavioral evidence s u p p o r t s this v i e w (Newsome, Wurtz, Dursteler, Mikami, J. Neurosci. 1985). On the o t h e r hand, B r a d d i c k (1974) s u g g e s t e d that t h e r e w e r e two d i f f e r e n t p r o c e s s e s in the p e r c e p t i o n of the a p p a r e n t m o t i o n ; One c h a r a c t e r i z e d by short times and small d i s p l a c e m e n t s (short r a n g e p r o c e s s ) , and the other characterized by l o n g e r times and larger displacements (long range p r o c e s s ) . In this e x p e r i m e n t , a l t e r n a t i n g r a n d o m d o t s s t i m u l i to test the s h o r t r a n g e p r o c e s s and a l t e r n a t i n g slit s t i m u l i to test the long r a n g e p r o c e s s w e r e presented to m e a s u r e the s p a t i a l limits to the p r o d u c t i o n of d i r e c t i o n a l response. Experiments were performed in a w a k e m a c a q u e monkeys trained to f i x a t e a p a i r of small s t a t i o n a l lines (0.225 X 0.075 deg). V i s u a l s t i m u l i w e r e p r e s e n t e d o n t o the CRT d i s p l a y s c r e e n (NEC K D - 5 5 1 ) of the p e r s o n a l c o m p u t e r (NEC PC-9801F). R a n d o m d o t s are c o m p o s e d of 0.075 deg d o t s and s h i f t b a c k and f o r t h in the p r e f e r r e d and null d i r e c t i o n s w i t h i n the r e c e p t i v e f i e l d of the n e u r o n . In a s i n g l e s e s s i o n , the t e m p o r a l i n t e r v a l (71, 141 or 283 msec) was f i x e d and the s p a t i a l i n t e r v a l was c h a n g e d r a n d o m l y 9 steps f r o m 0.0 to 4.8 deg. A f t e r s e v e r a l r e p e t i t i o n s in e a c h s p a t i a l i n t e r v a l was a c h i e v e d , a n e w s e s s i o n w i t h a new t e m p o r a l i n t e r v a l was s t a r t e d . A b o u t 60% (35/59) of d i r e c t i o n s e l e c t i v e MT neurons showed directional responses to a l t e r n a t i n g r a n d o m dots. The m a x i m u m spatial interval to p r o d u c e d i r e c t i o n a l response (dmax) was c a l c u l a t e d by a s i m i l a r m e t h o d to t h a t u s e d b e f o r e (Mikami, Newsome, Wurtz, J. N e u r o p h y s i o l . 1986). In m o s t c a s e s (20/24), d m a x for the a l t e r n a t i n g r a n d o m d o t s was l a r g e r than d m a x for the a l t e r n a t i n g slits. D m a x for b o t h r a n d o m d o t s and slits inc r e a s e s w h e n e c c e n t r i c i t y i n c - r e a s e s . It was s u g g e s t e d that MT n e u r o n s m i g h t be i n v o l v e d b o t h in the short r a n g e and long r a n g e p r o c e s s e s of the a p p a r e n t motion.
RESPONSE
MASAO AZUMA*, Sch. of Med.,
CURVE
YOSIHIRO Hirosaki
OF V I S U A L
NEURONS
S A S A K I * and 036, J a p a n
HISAO
IN THE M O N K E Y
SUZUKI,
Dept.
FRONTAL
EYE FIELD.
Physiol.,
Hirosaki
Univ.
The v i s u a l n e u r o n s in the m o n k e y f r o n t a l eye f i e l d r e s p o n d e d to a s t i m u l u s a p p e a r i n g in a r e s t r i c t e d p a r t (the r e c e p t i v e field) of the c o n t r a l a t e r a l h e m i field. F u r t h e r m o r e , t h e y w e r e o r g a n i z e d so as to r e p r e s e n t the a r e a f r o m the c e n t r a l to the p e r i p h e r a l v i s u a l f i e l d a c c o r d i n g to t h e i r l o c a t i o n in the c o r t i c a l area. The p u r p o s e of the p r e s e n t e x p e r i m e n t s is to i n v e s t i g a t e the s c o t o p i c a n d / o r p h o t o p i c p r o c e s s r e s p o n s i b l e for g e n e r a t i n g the v i s u a l r e s p o n s e of the neurons. We e x a m i n e d s p e c t r a l r e s p o n s e c h a r a c t e r i s t i c s of the n e u r o n s in the a w a k e m o n k e y u n d e r b o t h d a r k - and l i g h t - a d a p t e d s t a t e s . W h i l e the a n i m a l g a z e d at a small and d i m c e n t e r l i g h t spot, we p r e s e n t e d the s e c o n d l i g h t spot, 0.6 ° in d i a m e t e r for 1 s at the m o s t r e s p o n s i v e site in the v i s u a l f i e l d for e a c h n e u r o n , and e x a m i n e d its r e s p o n s e s . The s p o t w a s a m o n o c h r o m a t i c one r a n g i n g f r o m 400 to 700 nm in w a v e - l e n g t h in 2 0 - n m s t e p s of e q u a l e n e r g y . The i n t e n s i t y of the l i g h t w a s d e c r e a s e d by 0.2 l o g - u n i t s t e p s by n e u t r a l d e n s i t y f i l t e r u n t i l the t h r e s h o l d of the n e u r o n a l r e s p o n s e for e a c h w a v e - l e n g t h w a s d e t e r m i n e d , thus o b t a i n i n g the spectral threshold curve. In the l i g h t - a d a p t e d state, the v i s u a l n e u r o n r e s p o n d e d to e v e r y w a v e - l e n g t h m o n o c h r o m a t i c l i g h t of s t r o n g i n t e n s i t y . W h e n the i n t e n s i t y w a s d e c r e a s e d , the r a n g e of w a v e - l e n g t h for r e s p o n d i n g b e c a m e n a r r o w u n t i l no r e s p o n s e w a s o b t a i n e d at a b o u t a 1 log u n i t d e c r e a s e . W i t h this p r o c e d u r e , we o b t a i n e d s p e c t r a l t h r e s h o l d c u r v e s of a V s h a p e w i t h the l o w e s t t h r e s h o l d at a b o u t 560 nm. In the d a r k - a d a p t e d state, the t h r e s h o l d s w e r e at m o r e 3 log u n i t s and the c u r v e s w e r e s h i f t e d t o w a r d the d i r e c t i o n of s h o r t e r w a v e - l e n g t h (the Purkinje shift). The l o w e s t t h r e s h o l d w a s at 5 0 0 - 5 2 0 nm. It was c o n c l u d e d t h a t in s u c h h i g h e r v i s u a l c e n t e r s , b o t h p h o t o p i c a n d s c o t o p i c p r o c e s s e s c o n v e r g e to e a c h n e u r o n , m a k i n g a s p e c t r a l t h r e s h o l d c u r v e s i m i l a r to t h o s e of h u m a n v i s i o n .
RESPONSE MONKEY
TO
THE
AKICHIKA MIKAMI, Kyoto University,
ALTERNATING
RANDOM
DOT
STIMULI
Department of N e u r o p h y s i o l o g y , I n u y a m a , A i c h i 484, J a p a n
IN
THE
MT
Primate
NEURONS
Research
OF
MACAQUE
Institute,
The m i d d l e t e m p o r a l v i s u a l a r e a (MT) is an e x t r a s t r i a t e v i s u a l a r e a s that is selectively i n v o l v e d in the c o r t i c a l a n a l y s i s of v i s u a l m o t i o n . R e c e n t behavioral evidence s u p p o r t s this v i e w (Newsome, Wurtz, Dursteler, Mikami, J. Neurosci. 1985). On the o t h e r hand, B r a d d i c k (1974) s u g g e s t e d that t h e r e w e r e two d i f f e r e n t p r o c e s s e s in the p e r c e p t i o n of the a p p a r e n t m o t i o n ; One c h a r a c t e r i z e d by short times and small d i s p l a c e m e n t s (short r a n g e p r o c e s s ) , and the other characterized by l o n g e r times and larger displacements (long range p r o c e s s ) . In this e x p e r i m e n t , a l t e r n a t i n g r a n d o m d o t s s t i m u l i to test the s h o r t r a n g e p r o c e s s and a l t e r n a t i n g slit s t i m u l i to test the long r a n g e p r o c e s s w e r e presented to m e a s u r e the s p a t i a l limits to the p r o d u c t i o n of d i r e c t i o n a l response. Experiments were performed in a w a k e m a c a q u e monkeys trained to f i x a t e a p a i r of small s t a t i o n a l lines (0.225 X 0.075 deg). V i s u a l s t i m u l i w e r e p r e s e n t e d o n t o the CRT d i s p l a y s c r e e n (NEC K D - 5 5 1 ) of the p e r s o n a l c o m p u t e r (NEC PC-9801F). R a n d o m d o t s are c o m p o s e d of 0.075 deg d o t s and s h i f t b a c k and f o r t h in the p r e f e r r e d and null d i r e c t i o n s w i t h i n the r e c e p t i v e f i e l d of the n e u r o n . In a s i n g l e s e s s i o n , the t e m p o r a l i n t e r v a l (71, 141 or 283 msec) was f i x e d and the s p a t i a l i n t e r v a l was c h a n g e d r a n d o m l y 9 steps f r o m 0.0 to 4.8 deg. A f t e r s e v e r a l r e p e t i t i o n s in e a c h s p a t i a l i n t e r v a l was a c h i e v e d , a n e w s e s s i o n w i t h a new t e m p o r a l i n t e r v a l was s t a r t e d . A b o u t 60% (35/59) of d i r e c t i o n s e l e c t i v e MT neurons showed directional responses to a l t e r n a t i n g r a n d o m dots. The m a x i m u m spatial interval to p r o d u c e d i r e c t i o n a l response (dmax) was c a l c u l a t e d by a s i m i l a r m e t h o d to t h a t u s e d b e f o r e (Mikami, Newsome, Wurtz, J. N e u r o p h y s i o l . 1986). In m o s t c a s e s (20/24), d m a x for the a l t e r n a t i n g r a n d o m d o t s was l a r g e r than d m a x for the a l t e r n a t i n g slits. D m a x for b o t h r a n d o m d o t s and slits inc r e a s e s w h e n e c c e n t r i c i t y i n c - r e a s e s . It was s u g g e s t e d that MT n e u r o n s m i g h t be i n v o l v e d b o t h in the short r a n g e and long r a n g e p r o c e s s e s of the a p p a r e n t motion.