Brain Research, 159 (1978) 391-395 © Elsevier/North-Holland Biomedical Press
391
Influence of eccentricity on velocity characteristics of area 18 neurones in the cat
GUY A. ORBAN*, HENRY KENNEDY** and HUGO MAES Laboratorium voor Neuro- en Psychofysiologie, Campus Gasthuisberg, Herestraat, B-3000 Leuven (Belgium)
(Accepted August 31st, 1978)
Studies of the properties of area 18 neurones have suggested that this area in the cat is specifically concerned with the analysis of visual movementZ,9,12. All these studies were limited to small parts of area 18. One of the problems of determining the functional characteristics of area 18 is the large variability of its location on the cortex. Area 18 appears as an approximately 4 m m belt adjoining area 17, the 17-18 border constituting the vertical meridian (VM). Sulcal variation in the cat can be quite considerable s and it has been suggested that the lateral extent of area 17 and the location of the 17-18 border on the lateral gyrus is governed by the depth of the suprasplenial sulcus 3. Although 17 and 18 have been defined cytoarchitectually xx, the laminae in cat cortex are not always very clear and it is sometimes not easy to define a precise limit to area 185,6. The most useful criteria of whether one is recording in area 18 is the drift of receptive fields (RFs) away from the VM as the electrode goes away from the 17-18 border. Several authors have mapped areas 17 and 18 in this way1, 6,13. In order to examine the velocity characteristics of area 18 and the influence of eccentricity, we decided to combine both retinotopical mapping techniques and histological verification. Long penetrations were made starting in area 17 and passing into area 18. We attempted to correlate both the position of the R F in the retinotopical map and the functional characteristics with the cytoarchitecture. Qualitative (RF plotting and cell classification) and quantitative testing (construction of velocity response curves) of each neurone t o o k from 2 of 4 h. So that oblique penetrations from area 17 to 18 were to cover an adequate distance of the cortex to show movement of the R F with electrode displacement, it was essential for the preparation to be maintained for 4-6 days. Cats were initially anaesthetized with ketamine (Imalgene) and after the surgical procedure the animal was held by a painless head-holding device cemented to the skull and anaesthetized with a mixture of N20 and 02 (70:30). The animals were paralyzed by continuous infusion of a mixture of * Fellow of the National Research Council of Belgium. * ~ Present address: Laboratoire de Neuropsychologie Exp6rimentale, INSERM, Unit6 94, 16 av. Doyen L6pine, F-69500 Bron, France.
392 gallamine triethiodide (Flaxedil) at 7 - 9 mg/kg/h and D-tubocurarine at 0.4 mg/kg/h in 0.9 ~ saline. We found that the preparation could be maintained to a high standard by control of CO2 and rectal temperature and prevention of infection. Infection of the mucous membranes particularly of the conjunctivae of the eyes was prevented by intramuscular injection and local application to the eyes of a wide screen antibiotic (Terramycine). The optic discs were plotted 4 at the beginning and the end of each recording session. Qualitative testing of the neurones was done on a plotting table with hand-held stimuli. Once the RF was located and the cell classified according to the criteria of Kato et al. v, a computer-controlled visual stimulator was used for quantitative study. Our results confirm and extend those of Orban and Callens 10. We found both velocity-sensitive and velocity-specific neurones in area 18. The velocity-sensitive neurones respond to high velocities, giving a decreased response with velocities less than around 80-100 deg./sec. The velocity-specific neurones are tuned to a given velocity and show a decreased response at velocities above and below the optimum. The velocity-sensitive neurone can be considered as a high pass filter for velocity (e.g. cell K0618 in Fig. 2) and the velocity-tuned neurone as a narrow band filter (e.g. cell K0620 in Fig. 2). In a number of penetrations a hitherto undescribed velocity curve in cat visual cortex was found for neurones in area 18 situated close to the 17-18 border. These neurones responded to a wide range of velocities and can be considered as broad band filters for velocity. Cell K0605 (Fig. 2) is an example of the velocity curve of a broad band filter. This cell has a high discharge level and although the neurone responds to a wide range of velocities (0.7-700 deg./sec.) the change of the response with velocity is small. The neuronal response is measured as maximum firing rate calculated from the bin in the post-stimulus-time histogram(PSTH)with maximum spike count. Velocity response curves obtained with this measure very much depend on the bin width used for the construction of PSTHs. Cell K0605 was a simple cell with a small field (0.6 °) and the response duration at fast velocities was very short (20 msec). Applying Shannons' theorem, the bin width should be less than half the minimum duration of the response. Longer bin widths distort the velocity response curve by underevaluation of the response to fast velocities. For cell K0605 the ratio of the responses to the 3 fastest velocities tested (300, 500 and 700 deg./sec) to the response to the 3 slowest velocities tested (0.75, 1.2 and 2.2 deg./sec) calculated with a 4 msec bin width was 1.4, whilst a 32 msec bin width gave a ratio of only 0.47. This results from a selective decrement of the response to fast velocities with the larger bin width. A representative penetration is shown in Fig. I. The histological reconstruction of the tract was obtained from 60/zm thick cresyl violet-stained sections. The track is seen to enter into the cortex in area 17 and to pass into area 18. The border of 17 and 18 was defined after the criteria of Otsuka and Hassled I. However, the change in cytoarchitecture did not allow us to define the border with a precision greater than 300/~m. The tract remained parallel to the surface of the cortex and did not go deeper than layer III. The tract was situated in the frontal plane A1 and the fields were located 8 ° below the fixation point. Most (15/22) of the cells had a simple receptive field
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Fig. l. Upper part: histological reconstruction of an oblique penetration from area 17 into area 18, on a coronal section AI. The end of the electrode track is marked by two electrolytic lesions. The limits of layer 4 are drawn in dotted lines. The hatched zone indicates the transition zone between areas 17 and 18. Lower part: the RF drift along the electrode track. Full symbols indicate RF centre ofthe dominant eye (right eye) and open symbols indicate the binocular RF centre (mean of the position in the two eyes); circles indicate single cells and triangles multiunit recordings. The full line corresponds to that part of the track between entry into the cortex and the first lesion, the dotted line indicates the shift of the RFs between the two lesions. The numbers refer to the cells of which the velocity response curves are shown in Fig. 2. The arrow indicates the functional limit between 17 and 18 and the hatched zone indicates the histological transition zone. o r g a n i z a t i o n 7. A t 750 # m after the p o i n t o f e n t r y the velocity r e s p o n s e curves were seen to a b r u p t l y c h a n g e . F r o m cell K 0 6 0 5 o n w a r d s the n e u r o n e s b e c a m e r e s p o n s i v e t o fast velocities. T h i s c h a n g e i n velocity c h a r a c t e r i s t i c s was i n d e p e n d e n t o f a n y c h a n g e in R F size, t h e fields b e i n g very n a r r o w b e f o r e a n d after the c h a n g e o f velocity curves. A s
394 the electrode moved further laterally and the fields drifted away from the VM, the response velocity function progressively changed from a broad band filter type to a high pass filter type, by a decrease o f the response to slow velocities and an increase o f the response to fast velocities. Together with this change in velocity response curves there was a modification of the influence o f velocity on the response latency. The latencies o f neurones K0605, K0611 and K0618 were seen to be a negative power function o f velocity, but the slope of the function increased progressively as the response to fast movements improved. In this penetration the drift o f fields and the change in functional characteristics very nearly coincided. Fig. 1 further illustrates two factors which can make the inflexion o f R F drift at the 17-18 border difficult to objectivate in short penetrations. First there is the high magnification near the V M (see also Fig. 2 o f ref. 6) which gives rise to a very small m o v e m e n t o f the fields as the electrode proceeds across the cortex. Second the degree o f scatter of the R F can be quite considerable. In this penetration, as in others, the functional definition of area 18 (i.e. determination o f the medial limit of area 18 based on R F drift and cell response to
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Fig. 2. Velocity response curves of 6 neurones (out of a total of 15) recorded in the penetration of Fig. l. All curves are plotted on a bilogarithrnic scale except in the case of K0620. Maximum firing rate is plotted as a function of velocity. The dotted lines indicate the highest spontaneous firing rate of each cell. The position of the neurones along the electrode track is indicated in Fig. 1. All cells had simple RFs except K0604 which was a hypercomplex I cell.
395 velocity) was seen to fall at the very beginning o f the zone where the c y t o a r c h i t e c t u r e i n d i c a t e d the 17-18 b o r d e r . Oblique p e n e t r a t i o n s f r o m area 17 to 18 show t h a t velocity characteristics o f the n e u r o n e s can give a s h a r p d e l i m i t a t i o n o f b o t h areas, at least in the frontal planes e x p l o r e d (A2 to P2.5) a n d for R F s below the fixation p o i n t (3 ° to 10°). This limit a p p r o x i m a t i v e l y c o r r e s p o n d s to the inflexion o f the R F drift. There is a close c o r r e l a t i o n between position in visual space and f u n c t i o n a l characteristics. The R F drift a n d the f u n c t i o n a l characteristics were f o u n d to change at the c o m m e n c e m e n t o f the histological t r a n s i t i o n zone. These results underline the difficulties o f interpreting the d a t a o b t a i n e d in vertical p e n e t r a t i o n s into the lateral gyrus close to the p r o j e c t i o n o f the fixation p o i n t or the vertical meridian. T h e oblique p e n e t r a t i o n s also show t h a t at c o m p a r a b l e eccentricities a r e a 18 neurones r e s p o n d to a m u c h faster range o f velocities t h a n a r e a 17 neurones. This fact indicates t h a t areas 17 a n d 18 n o t only c o n s t i t u t e different m a p s o f visual space b u t also are involved in a different t r e a t m e n t o f visual i n f o r m a t i o n . F u r t h e r m o r e , the systematic change in the velocity characteristics e n c o u n t e r e d as the electrode moves a w a y f r o m the V M underlines the i m p o r t a n c e o f velocity as a stimulus p a r a m e t e r for a r e a 18 neurones. F u r t h e r e x p e r i m e n t a t i o n is u n d e r w a y to elucidate h o w eccentricity governs the velocity t u n i n g at o t h e r a n t e r i o r p o s t e r i o r levels. This research was p a r t l y s u p p o r t e d b y G r a n t s A D G D4991 a n d A D G F163 o f the N a t i o n a l R e s e a r c h Council o f Belgium (to G.O.). 1 Bilge, M., Bingle, A., Seneviratne, K. N. and Whitteridge, D., A map of the visual cortex in the cat, J. PhysioL (Lond.), 191 (1967) l16P-I19P. 2 Cynader, M. and Regan, D., Neurones in cat parastriate cortex sensitive to the direction of motion in three-dimensional space, J. PhysioL (Lond.), 274 (1978) 549-569. 3 Donaldson, I. M. L. and Whitteridge, D., The nature of the boundary between cortical visual areas II and III in the cat, Proc. roy Soc. B, 199 (1977) 445-462. 4 Fernald, R. and Chase, R., An improved method for plotting retinal landmarks and focusing the eyes, Vision Res., 11 (1971)95-96. 5 Fisken, R. A., Garey, L. J. and Powell, T. P. S., The intrinsic, association and commissural connections of area 17 of the visual cortex, Phil. Trans. B, 272 (1975) 487-536. 6 Hubel, D. H. and Wiesel, T. N., Receptive fields and functional architecture in two nonstriate visual areas (18 and 19) of the cat, J. Neurophysiol., 28 (1965) 229-289. 7 Kato, H., Bishop, P. O. and Orban, G. A., Hypercomplex and the simple/complexcell classifications in the cat striate cortex, J. NeurophysioL, 41 (1978) 1071-1095. 8 Kawarnura, K., Variations of the cerebral sulci in the cat. Acta anat. (Basel), 80 (1971) 204-221. 9 0 r b a n , G. A., Area 18 of the cat: the first step in processing visual movement information, Perception, 6 (1977) 501-511. 10 Orban, G. A. and Callens, M., Influence of movement parameters on area 18 neurones in the cat, Exp. Brain Res., 30 (1977) 125-140. 11 Otsuka, R. und Hassler, R., Uber Autbau und Gliederung der corticalen Sehsph~ire bei der Katze, Arch. Psychiat. Nervenkr., 203 (1962) 212-234. 12 Tretter, F., Cynader, M. and Singer, W., Cat parastriate cortex: a primary or secondary visual area? J. NeurophysioL, 38 (1975) 1099-1113. 13 Tusa, R. J., Palmer, L. A. and Rosenquist, A. C., The retinotopic organization of area 17 (striate cortex) in the cat, J. comp. NeuroL, 177 (1978) 213-236.
391
Influence of eccentricity on velocity characteristics of area 18 neurones in the cat
GUY A. ORBAN*, HENRY KENNEDY** and HUGO MAES Laboratorium voor Neuro- en Psychofysiologie, Campus Gasthuisberg, Herestraat, B-3000 Leuven (Belgium)
(Accepted August 31st, 1978)
Studies of the properties of area 18 neurones have suggested that this area in the cat is specifically concerned with the analysis of visual movementZ,9,12. All these studies were limited to small parts of area 18. One of the problems of determining the functional characteristics of area 18 is the large variability of its location on the cortex. Area 18 appears as an approximately 4 m m belt adjoining area 17, the 17-18 border constituting the vertical meridian (VM). Sulcal variation in the cat can be quite considerable s and it has been suggested that the lateral extent of area 17 and the location of the 17-18 border on the lateral gyrus is governed by the depth of the suprasplenial sulcus 3. Although 17 and 18 have been defined cytoarchitectually xx, the laminae in cat cortex are not always very clear and it is sometimes not easy to define a precise limit to area 185,6. The most useful criteria of whether one is recording in area 18 is the drift of receptive fields (RFs) away from the VM as the electrode goes away from the 17-18 border. Several authors have mapped areas 17 and 18 in this way1, 6,13. In order to examine the velocity characteristics of area 18 and the influence of eccentricity, we decided to combine both retinotopical mapping techniques and histological verification. Long penetrations were made starting in area 17 and passing into area 18. We attempted to correlate both the position of the R F in the retinotopical map and the functional characteristics with the cytoarchitecture. Qualitative (RF plotting and cell classification) and quantitative testing (construction of velocity response curves) of each neurone t o o k from 2 of 4 h. So that oblique penetrations from area 17 to 18 were to cover an adequate distance of the cortex to show movement of the R F with electrode displacement, it was essential for the preparation to be maintained for 4-6 days. Cats were initially anaesthetized with ketamine (Imalgene) and after the surgical procedure the animal was held by a painless head-holding device cemented to the skull and anaesthetized with a mixture of N20 and 02 (70:30). The animals were paralyzed by continuous infusion of a mixture of * Fellow of the National Research Council of Belgium. * ~ Present address: Laboratoire de Neuropsychologie Exp6rimentale, INSERM, Unit6 94, 16 av. Doyen L6pine, F-69500 Bron, France.
392 gallamine triethiodide (Flaxedil) at 7 - 9 mg/kg/h and D-tubocurarine at 0.4 mg/kg/h in 0.9 ~ saline. We found that the preparation could be maintained to a high standard by control of CO2 and rectal temperature and prevention of infection. Infection of the mucous membranes particularly of the conjunctivae of the eyes was prevented by intramuscular injection and local application to the eyes of a wide screen antibiotic (Terramycine). The optic discs were plotted 4 at the beginning and the end of each recording session. Qualitative testing of the neurones was done on a plotting table with hand-held stimuli. Once the RF was located and the cell classified according to the criteria of Kato et al. v, a computer-controlled visual stimulator was used for quantitative study. Our results confirm and extend those of Orban and Callens 10. We found both velocity-sensitive and velocity-specific neurones in area 18. The velocity-sensitive neurones respond to high velocities, giving a decreased response with velocities less than around 80-100 deg./sec. The velocity-specific neurones are tuned to a given velocity and show a decreased response at velocities above and below the optimum. The velocity-sensitive neurone can be considered as a high pass filter for velocity (e.g. cell K0618 in Fig. 2) and the velocity-tuned neurone as a narrow band filter (e.g. cell K0620 in Fig. 2). In a number of penetrations a hitherto undescribed velocity curve in cat visual cortex was found for neurones in area 18 situated close to the 17-18 border. These neurones responded to a wide range of velocities and can be considered as broad band filters for velocity. Cell K0605 (Fig. 2) is an example of the velocity curve of a broad band filter. This cell has a high discharge level and although the neurone responds to a wide range of velocities (0.7-700 deg./sec.) the change of the response with velocity is small. The neuronal response is measured as maximum firing rate calculated from the bin in the post-stimulus-time histogram(PSTH)with maximum spike count. Velocity response curves obtained with this measure very much depend on the bin width used for the construction of PSTHs. Cell K0605 was a simple cell with a small field (0.6 °) and the response duration at fast velocities was very short (20 msec). Applying Shannons' theorem, the bin width should be less than half the minimum duration of the response. Longer bin widths distort the velocity response curve by underevaluation of the response to fast velocities. For cell K0605 the ratio of the responses to the 3 fastest velocities tested (300, 500 and 700 deg./sec) to the response to the 3 slowest velocities tested (0.75, 1.2 and 2.2 deg./sec) calculated with a 4 msec bin width was 1.4, whilst a 32 msec bin width gave a ratio of only 0.47. This results from a selective decrement of the response to fast velocities with the larger bin width. A representative penetration is shown in Fig. I. The histological reconstruction of the tract was obtained from 60/zm thick cresyl violet-stained sections. The track is seen to enter into the cortex in area 17 and to pass into area 18. The border of 17 and 18 was defined after the criteria of Otsuka and Hassled I. However, the change in cytoarchitecture did not allow us to define the border with a precision greater than 300/~m. The tract remained parallel to the surface of the cortex and did not go deeper than layer III. The tract was situated in the frontal plane A1 and the fields were located 8 ° below the fixation point. Most (15/22) of the cells had a simple receptive field
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Fig. l. Upper part: histological reconstruction of an oblique penetration from area 17 into area 18, on a coronal section AI. The end of the electrode track is marked by two electrolytic lesions. The limits of layer 4 are drawn in dotted lines. The hatched zone indicates the transition zone between areas 17 and 18. Lower part: the RF drift along the electrode track. Full symbols indicate RF centre ofthe dominant eye (right eye) and open symbols indicate the binocular RF centre (mean of the position in the two eyes); circles indicate single cells and triangles multiunit recordings. The full line corresponds to that part of the track between entry into the cortex and the first lesion, the dotted line indicates the shift of the RFs between the two lesions. The numbers refer to the cells of which the velocity response curves are shown in Fig. 2. The arrow indicates the functional limit between 17 and 18 and the hatched zone indicates the histological transition zone. o r g a n i z a t i o n 7. A t 750 # m after the p o i n t o f e n t r y the velocity r e s p o n s e curves were seen to a b r u p t l y c h a n g e . F r o m cell K 0 6 0 5 o n w a r d s the n e u r o n e s b e c a m e r e s p o n s i v e t o fast velocities. T h i s c h a n g e i n velocity c h a r a c t e r i s t i c s was i n d e p e n d e n t o f a n y c h a n g e in R F size, t h e fields b e i n g very n a r r o w b e f o r e a n d after the c h a n g e o f velocity curves. A s
394 the electrode moved further laterally and the fields drifted away from the VM, the response velocity function progressively changed from a broad band filter type to a high pass filter type, by a decrease o f the response to slow velocities and an increase o f the response to fast velocities. Together with this change in velocity response curves there was a modification of the influence o f velocity on the response latency. The latencies o f neurones K0605, K0611 and K0618 were seen to be a negative power function o f velocity, but the slope of the function increased progressively as the response to fast movements improved. In this penetration the drift o f fields and the change in functional characteristics very nearly coincided. Fig. 1 further illustrates two factors which can make the inflexion o f R F drift at the 17-18 border difficult to objectivate in short penetrations. First there is the high magnification near the V M (see also Fig. 2 o f ref. 6) which gives rise to a very small m o v e m e n t o f the fields as the electrode proceeds across the cortex. Second the degree o f scatter of the R F can be quite considerable. In this penetration, as in others, the functional definition of area 18 (i.e. determination o f the medial limit of area 18 based on R F drift and cell response to
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Fig. 2. Velocity response curves of 6 neurones (out of a total of 15) recorded in the penetration of Fig. l. All curves are plotted on a bilogarithrnic scale except in the case of K0620. Maximum firing rate is plotted as a function of velocity. The dotted lines indicate the highest spontaneous firing rate of each cell. The position of the neurones along the electrode track is indicated in Fig. 1. All cells had simple RFs except K0604 which was a hypercomplex I cell.
395 velocity) was seen to fall at the very beginning o f the zone where the c y t o a r c h i t e c t u r e i n d i c a t e d the 17-18 b o r d e r . Oblique p e n e t r a t i o n s f r o m area 17 to 18 show t h a t velocity characteristics o f the n e u r o n e s can give a s h a r p d e l i m i t a t i o n o f b o t h areas, at least in the frontal planes e x p l o r e d (A2 to P2.5) a n d for R F s below the fixation p o i n t (3 ° to 10°). This limit a p p r o x i m a t i v e l y c o r r e s p o n d s to the inflexion o f the R F drift. There is a close c o r r e l a t i o n between position in visual space and f u n c t i o n a l characteristics. The R F drift a n d the f u n c t i o n a l characteristics were f o u n d to change at the c o m m e n c e m e n t o f the histological t r a n s i t i o n zone. These results underline the difficulties o f interpreting the d a t a o b t a i n e d in vertical p e n e t r a t i o n s into the lateral gyrus close to the p r o j e c t i o n o f the fixation p o i n t or the vertical meridian. T h e oblique p e n e t r a t i o n s also show t h a t at c o m p a r a b l e eccentricities a r e a 18 neurones r e s p o n d to a m u c h faster range o f velocities t h a n a r e a 17 neurones. This fact indicates t h a t areas 17 a n d 18 n o t only c o n s t i t u t e different m a p s o f visual space b u t also are involved in a different t r e a t m e n t o f visual i n f o r m a t i o n . F u r t h e r m o r e , the systematic change in the velocity characteristics e n c o u n t e r e d as the electrode moves a w a y f r o m the V M underlines the i m p o r t a n c e o f velocity as a stimulus p a r a m e t e r for a r e a 18 neurones. F u r t h e r e x p e r i m e n t a t i o n is u n d e r w a y to elucidate h o w eccentricity governs the velocity t u n i n g at o t h e r a n t e r i o r p o s t e r i o r levels. This research was p a r t l y s u p p o r t e d b y G r a n t s A D G D4991 a n d A D G F163 o f the N a t i o n a l R e s e a r c h Council o f Belgium (to G.O.). 1 Bilge, M., Bingle, A., Seneviratne, K. N. and Whitteridge, D., A map of the visual cortex in the cat, J. PhysioL (Lond.), 191 (1967) l16P-I19P. 2 Cynader, M. and Regan, D., Neurones in cat parastriate cortex sensitive to the direction of motion in three-dimensional space, J. PhysioL (Lond.), 274 (1978) 549-569. 3 Donaldson, I. M. L. and Whitteridge, D., The nature of the boundary between cortical visual areas II and III in the cat, Proc. roy Soc. B, 199 (1977) 445-462. 4 Fernald, R. and Chase, R., An improved method for plotting retinal landmarks and focusing the eyes, Vision Res., 11 (1971)95-96. 5 Fisken, R. A., Garey, L. J. and Powell, T. P. S., The intrinsic, association and commissural connections of area 17 of the visual cortex, Phil. Trans. B, 272 (1975) 487-536. 6 Hubel, D. H. and Wiesel, T. N., Receptive fields and functional architecture in two nonstriate visual areas (18 and 19) of the cat, J. Neurophysiol., 28 (1965) 229-289. 7 Kato, H., Bishop, P. O. and Orban, G. A., Hypercomplex and the simple/complexcell classifications in the cat striate cortex, J. NeurophysioL, 41 (1978) 1071-1095. 8 Kawarnura, K., Variations of the cerebral sulci in the cat. Acta anat. (Basel), 80 (1971) 204-221. 9 0 r b a n , G. A., Area 18 of the cat: the first step in processing visual movement information, Perception, 6 (1977) 501-511. 10 Orban, G. A. and Callens, M., Influence of movement parameters on area 18 neurones in the cat, Exp. Brain Res., 30 (1977) 125-140. 11 Otsuka, R. und Hassler, R., Uber Autbau und Gliederung der corticalen Sehsph~ire bei der Katze, Arch. Psychiat. Nervenkr., 203 (1962) 212-234. 12 Tretter, F., Cynader, M. and Singer, W., Cat parastriate cortex: a primary or secondary visual area? J. NeurophysioL, 38 (1975) 1099-1113. 13 Tusa, R. J., Palmer, L. A. and Rosenquist, A. C., The retinotopic organization of area 17 (striate cortex) in the cat, J. comp. NeuroL, 177 (1978) 213-236.
