Ferrier Lecture: The Organization of the Visual Cortex in Man

Ferrier Lecture: The Organization of the Visual Cortex in ManAuthor(s): Gordon HolmesSource: Proceedings of the Royal Society of London. Series B, Biological Sciences, Vol. 132, No.869 (Apr. 10, 1945), pp. 348-361Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/82307 .

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Ferrier Lecture

The organization of the visual cortex in man

By Gordon Holmes, F.R.S.

(Delivered 18 May 1944?Received 26 June 1944)

In this lecture, which was founded to commemorate the pioneer work of Sir David

Ferrier on cerebral localization, I intend to deal with a subject in which he was

particularly interested, that is the cortical representation of vision.

Ferrier's interest was at once excited by the discovery of Fritsch & Hitzig (1870) that certain portions of the surface of the forebrain are excitable, and he im?

mediately adopted this new method of electrical stimulation to map out those

areas from which movements can be produced. The results of his investigations on the motor cortex are well known, but he also discovered that movements could

be elicited from other regions which he did not regard as primarily motor, including deviations of the eyes on stimulation of the angular gyrus on the lateral surface

of the parietal lobe. He interpreted these movements as motor responses to

'excitation of subjective visual sensations' by the stimulus, and he therefore

assumed that this region contained the primary visual centres, that is the centres

through which retinal impressions excite visual perception. A series of experiments on monkeys which he reported in the Croonian Lecture of 1875 appeared to sup?

port this conclusion, for he found that destruction of one angular gyrus caused

blindness of the opposite eye, which was not, however, permanent if the other

angular gyrus was intact (Fig. 1). Ablation of both angular gyri appeared to cause

complete and permanent loss of vision. He failed to detect any disturbance of

sight when one occipital lobe only was injured, provided the lesion did not extend

forwards to the angular gyrus. At about the same time, however, Hitzig (1874) brought forward evidence that

the visual area lay in the occipital lobe; this was later confirmed by Munk (1881), Schafer (1888) and others. The disorders of sight which Ferrier observed were

probably due to injury of the optic radiations, which are the final link in the visual

pathway to the cortex, for these lie close to the surface of the brain beneath the

angular gyrus, or to damage of them by softening or infection, for his operations were not performed under aseptic conditions. As in the rhesus monkey, which he

employed in his experiments, the majority of the fibres of each optic nerve cross

to the opposite side in the chiasma, cerebral lesions cause greater loss of vision in

the opposite eye. The preservation of sight in animals from which he removed the occipital lobes

must, on the other hand, have been due to incomplete excision of the visual cortex, which in the monkey extends a considerable distance over the lateral surface of

[ 348 ]



Ferrier Lecture 349

the hemisphere (figure 2). It is in this connexion significant that he observed dis?

turbances of vision from occipital lesions only when the injury extended forwards

to the angular gyrus; it is now known that that area of the cortex which by its

structure marks out the visual receptive area in the monkey reaches almost to the

posterior limb of the angular gyrus, and that it is here that central vision is repre?

sented, so injury of this part of it would cause most obvious disturbances of sight. On the other hand, any removal not extending to this limit would leave some

cortex available for vision.

? RckIo prawentrnllK R. |K>?.confr.

.'_

Figure 1. The shaded areas indicate the

positions of lesions of the cortex of the

monkey which, according to Ferrier, produce blindness. (Ferrier, Functions of the Brain.)

Figure 2. The extent of the striate area, or field 17, which is marked by dots, in the

monkey.

Though Munk, Schafer and other physiologists established the visual centre in

the occipital lobe its more exact delimitation was determined only by clinicians

who were able to correlate defects in the fields of vision with local lesions of the

cortex found on post-mortem examination. This was largely due to Henschen

(1890-94), of Stockholm, who, from his own observations and from numerous

others recorded in medical literature, collected evidence that in man the visual

receptive area coincides with that portion of the cortex around the calcarine

fissure which is distinguished by a horizontal band of medullated fibres and is

consequently known as the striate area (figure 3). This has been adequately con?

firmed by other methods of investigation, as by Bolton (1900), who demonstrated

Vol. 132. B. 24



350 G. Holmes

changes limited to it after removal of the eyes, and particularly by more recent

anatomical work by Brouwer (1930) and his fellow workers, by Polyak (1933) and

by Le Gros Clark (1941), who found this to be the cortical termination of the chain

of neurons which carry retinal impulses to the forebrain. Further evidence that

the visual cortex corresponds with the striate area is provided by more recent

physiological investigations. Von Bonin, Garol & McCulloch (1942) have, for

instance, found that the cortical responses to a flash of light in the eyes are restricted

to it.

Figure 3. The striate area, or field 17, in the human brain. A large part of it is buried in the calcarine fissure.

But though it was more or less definitely settled that the striate area is the

cortical centre for vision, there was, prior to 1914, no definite evidence of the local

representation of the retina within it. Even the portion concerned in central or

macular vision was ia dispute; by some it was placed anteriorly, by others pos?

teriorly. It is historically interesting that nearly sixty years ago Schafer (1888)

suggested, from his observations on the movements of the eyes evoked by stimula?

tion of the occipital lobe, a definite projection of the retina on the cortex which

corresponds approximately to that which is now generally accepted.

My own work on the visual cortex has been limited to observation on man.

Approach to the subject has been purely clinical and has been based mainly on

observations on the effects of gunshot wounds of it during the war of 1914-18, but



Ferrier Lecture 351

it has been amplified by later investigations. This has required the collection of a

large number of observations, for while the physiologist can rely on experiments which he can select and control, and can obtain from them more precise, sometimes

critical and often measurable data, the clinician must depend on the analysis of

observations which are rarely so simple or clear cut, and he is often unable to

correlate them with the causal lesions responsible for them. The physiologist may be compared with the builder in ashlar or hewn stones which can easily be fitted

together, the physician resembles the mason who has to use irregular rubble and

therefore requires more time and labour to attain his end. But in some branches

of neurology the 'rubble' collected and put together by the clinician is essential, or can at least be complementary to the conclusions of the experimentalist. This

is particularly so in the investigation of those functions of the brain which require the co-operation of a conscious subject who is able to communicate his experiences, as in the examination of sensory functions.

Figure 4. Right homonymous hemianopia, or blindness of the right halves of the fields of vision, due to destruction of the left striate area.

Owing to the decussation in man of the fibres of each optic nerve which comes

from the nasal or median portion of each retina, complete destruction of the striate

area of one hemisphere of the brain causes homonymous hemianopia to the

opposite side, that is blindness of the ipsilateral nasal and of the contralateral

temporal halves of the fields of vision (figure 4). Gunshot wounds generally produce less extensive damage, and, by relating the loss in the visual fields with the position of the wound or missile, it has been possible to construct a map of the visual

cortex on which the cortical area related to each segment of the retina can be

shown (figure 5). Analysis of the visual disturbances produced by such local lesions

demonstrated that the upper portion of the striate area corresponds to the upper

24-2



352 G. Holmes

part of the retina and consequently receives impressions from the lower portions of the fields of vision; that the lower segments of the retinae are represented in the

lower portion of the striate area; that the maculae, which subserve central vision,

are represented posteriorly; that the peripheries of the retinae along the vertical

meridians correspond with the upper and lower margins of the striate area, and

Figure 5. On the left the striate area of the left hemisphere of the brain is shown, the cal? carine fissure being opened up to reveal that portion of it which lines its walls. On the right is the right half of one visual field. The correspondence of the markings indicates the repre? sentation of different segments of the visual field on the cortex.

the sectors which adjoin the horizontal meridians with the cortex in the depth of

the calcarine fissure. The retinal projection on the cortex may, in fact, be repre? sented by picturing one half of a retina spread over the surface of one striate area,

the macular region being placed posteriorly, the periphery anteriorly, the upper

margin along its upper edge and the lower on its inferior border. These observations,

therefore, indicate a geographical projection, or point-to-point localization, of the

retina in the cortex.

This projection is not, however, uniform in the sense that each portion of the

cortex corresponds to a proportionately equal segment of the retina, for the cor-



Ferrier Lecture 353

tical representation of the more highly evolved and specialized maculae, which

subserve central vision, occupies a relatively very much greater portion of the

striate area than peripheral parts. Marshall & Talbot (1942) have also found that

in the cat and monkey the area of the cortex in which electrical changes are excited

by photic stimulation of the macular region is enormously greater than that which

responds directly to stimulation of the periphery of the retina. In this respect the

projection of the retina on the cortex conforms to that of motor representation where, for example, the centres of the more voluntary, more complex arid more

specialized movements of the hand and fingers are relatively much more exten?

sive than those of the larger, but cruder and more automatic, movements of the

proximal segments of the arm.

These conclusions, arrived at by investigation of the visual disturbances pro? duced by local gunshot injuries of the occipital lobe, supplemented by observations

on the effects of local vascular and other lesions of the striate area, indicate that

each point of the retina is sharply represented in a corresponding point of the

visual cortex.

All evidence that has accumulated since 1918 goes to confirm the existence of

this point-to-point projection of the retinae in the cortex. In addition to clinical

observations, anatomical investigations by Brouwer (1930), Le Gros Clark (1941) and others have shown that optic nerve fibres which convey impulses from each

segment of the retinae end in sharply defined regions of the lateral geniculate

bodies, and Le Gros Clark particularly has demonstrated that there is a very

precise projection of the latter on the visual cortex. These anatomical connexions

provide a straight and direct path from each retinal point to a corresponding point in the striate area. Physiological investigations by Talbot & Marshall (1941)

point to the same conclusion, for by recording potentials excited in the cortex by

point stimulation of the retina in the rhesus monkey they were able to map out

the projection of separate segments of the retina on it. They emphasize, however,

that a point-to-point projection can be accepted only in a dynamic sense.

The fact that a small area of loss of vision, often not exceeding a visual angle of

a few degrees, may remain unchanged for years also suggests a rigid and exclusive

relation of retina and cortex (figure 6).

Though there is much evidence in favour of the view that each point of the

retina is projected exclusively on to a corresponding point of the cortex, other

anatomical facts suggest that retinal impulses may be distributed more widely. Minkowski (1920) pointed out that as each retinal receptor is, owing to the branch?

ing of its fibres and the interposition of intercalated neurons, connected with more

than one ganglion cell, impulses from it can pass along several optic nerve fibres

to the lateral geniculate body. There are no intercalated cells in the latter, but as

Le Gros Clark & Glees (1941) have found that each fibre from the retina ends on

several geniculate cells, there must be a further diffusion of impulses here, and

when these reach the cortex a further dispersion can occur owing to intracortical

association neurons. Lorente de No (1934) has also concluded that impulses from



354 G. Holmes

each point of the retina reach a relatively large area of the cortex, but as the

threshold of excitation in the latter is attained only when a number of its synapses are excited, the functional projection of the retina may be punctate. Marshall &

Talbot (1942) also accept reciprocal over-lap and multiplication of pathways of

retinal impulses, but conclude that there is one primary cortical focus for each foveal

cone at least.

Figure 6. The loss of vision due to a small penetrating wound of the upper part of the

posterior portion of the striate area of the right side. The blind areas remained unaltered for more than four years after the infliction of the wound.

Such a rigid functional relation of periphery and cortex as the point-to-point

hypothesis assumes apparently does not exist in other cerebral systems. High

organization of function dependent on firmly established nervous connexions, and

consequently certainty and invariability of response, is a characteristic of lower

levels of the nervous system; it is not found in the other reactions of the cortex

which are capable of experimental analysis. In the motor cortex, where study of

function is more accessible to experimental observation, Graham Brown & Sher?

rington (1912) have shown that the response from any point in it is not constant; it may be altered by previous happenings and by other factors, and may even be

reversed. For instance, a flexor movement may be elicited from a point the

ordinary response of which is extension of the same joint. There is evidence that

in man too the functions of the motor cortex are modifiable, for if after the flexor

and extensor tendons of a joint have been divided the proximal ends of the flexors

are sutured to the distal portions of the extensors, and vice versa, the subject may learn to use his joint naturally. To do so he must send out along paths which

normally carry flexor impulses messages which produce an extensor movement; a certain readjustment of function to meet new conditions has developed.

These facts c^n be interpreted only by assuming that it is function, not ana?

tomical structures, which is represented in the motor cortex, and that the functions

so represented are to some extent plastic or modifiable.



Ferrier Lecture 355

It is dangerous to transfer conclusions arrived at from a study of the motor to

a receptive area, as the visual cortex, more particularly as the latter is phylo-

genetically older and more highly organized. Adrian (1939) has, however, pointed out that facilitation, on which deviation of motor response depends, is not con?

fined to the motor area, and Bartley & Bishop (1933) have found that stimulation

of one fibre of an optic nerve may increase the response caused by excitation of

other fibres.

Is there any evidence of similar plasticity in the organization of the visual

cortex?

In the case of vision the only definite differentiation of function is of central, or macular, as compared with peripheral sight. Macular vision is characterized

by greater acuity, a greater power of discrimination, more accurate projection into space of images perceived through it, and more exact fixation of objects seen by it.

Certain clinical observations do indicate that under pathological conditions these

properties of macular or central vision may be taken over by extra-macular or

peripheral vision as a result of modifications in the functional activity of the cortex.

Complete destruction of one striate area in man produces, as we have seen,

hemianopia, or complete blindness of the opposite side of the visual field of each

eye, which often extends up to and bisects the fixation point. The patient is,

however, frequently unaware of this loss of half his visual space, or learns it only

by experience. The visual space that remains appears to him unrestricted and to

extend to right and left and up and down, as the normal field of vision does. In

other words the subjective field of vision is undiminished though the objective field is halved. This loss of vision to one side is a considerable disability, but in?

ability to see one half of an object the image of which falls on the maculae is a

more serious handicap. It is got over partly by psychological completion of the

object on which his gaze is directed if it is familiar, for instance a circle part of

which only is visible may be apprehended as a whole. Similar completion occurs

normally, for we see an object as a whole even when part of its image falls on the

blind spot. In certain cases of hemianopia vision is extended to the blind side by employing

in fixation, not the fovea, but a point in the retina on its seeing side. The subjective field of vision, that is the visual space of which the patient is aware at any moment,

is shifted towards the blind side and a useful extension of sight around the fixation

point is acquired. The sensitivity of this new point employed in central vision may

eventually approximate to that of the macula. It becomes the centre of attention

and is consequently employed in fixation. Images that fall on it are projected

correctly and it therefore serves for accurate localization in external space. Such a point outside the macula which, when hemianopia exists, may be em?

ployed in fixation and for distinct vision has been named a ' pseudofovea' by

German workers (Fuchs 1920; Best 1917; Kleist 1934), who have studied its

appearance. Various explanations of its development have been offered. There is



356 G. Holmes

probably a conscious factor, for a patient may find he sees more fully and more

distinctly by directing his gaze towards the blind side of the object which interests

him than by using the normal macula at which he can see half of it only. The fact

that a pseudofovea generally disappears when he becomes aware of his half-blind?

ness indicates the importance of psychological factors. Visual attention probably has a larger part in the development of a pseudofovea, for in hemianopia attention

can roam over half of visual space only and is less firmly held by central vision, where its play is at once obstructed by a barrier of blindness, than by vision sub?

served by an adjacent point in the retina. The latter point may then become the

focus of attention. Its development is facilitated by the fact that during fixation

the eyes oscillate in order that different portions of the image of the object on

which attention is directed move over the fovea, and if during these excursions a

more complete picture is obtained when the image falls on a point outside the fovea

this point may become the centre of attention and it is then employed in auto?

matic fixation.

Though the pseudofovea is used in ordinary inspection when fullest and most

distinct vision is required, on voluntary fixation, or firm gaze, the eyes are directed

to the object so that its image falls on the true fovea. Consequently in ordinary

perimetric examination, which requires voluntary fixation, the presence of a shift

of the field of vision towards the blind side is rarely obvious. Its presence is,

however, shown by the fact that when a patient suffering with recent hemianopia

attempts to grasp an object quickly his hand often fails to reach it directly; the

errors are almost invariably towards the blind side as the image that falls on the

pseudofovea is projected to this side of the visual axis.

These observations indicate that when vision to one side is lost a point in the

retina outside the macula can develop functions that normally belong to the

macula, that is most distinct vision, exact fixation, accurate projection of the image

perceived by it into space, and correct localization in space. It also becomes the

centre or focus of attention.

The development of these new properties must be interpreted as due to modi?

fications of function in the visual cortex, not to changes in the retina, which is a

highly organized tissue.

Further evidence that the functions of the visual cortex are not solely and

rigidly determined by such anatomical connexions as a point-to-point projection of the retinae on it may suggest, is furnished by a study of vision when one eye

squints, provided there is no serious defect of vision in either eye. Under normal conditions accurate sight and stereoscopic vision require that,

in order that they be fused into a single perception, images of an object on which

gaze is directed should fall on corresponding points of the two retinae. If, owing to non-parallelism of the visual axes in fixation, the images fall on non-corre?

sponding points and are projected separately into space the subject experiences

diplopia or double vision. When, however, the squint is congenital or of long

standing he may not have double vision, though the images of the object fall on



Ferrier Lecture 357

disparate points. In these circumstances a point in the periphery of the retina of

the squinting eye develops a physiological correspondence with the fovea of the

normal eye. This point, which is known as a 'false macula', acquires many of the

functions of the true macula. The image that falls on it may be clearer and more

distinct than that normally perceived by the periphery of the retina, it is projected

accurately into space, and when both eyes are employed in fixation it may fuse

with the foveal image of the opposite eye to subserve accurate binocular and

stereoscopic vision. The false macula of the squinting eye has developed functions

of the true macula and has become the centre of visual orientation.

When such a squint is corrected by surgical operation which brings the visual

axes parallel on binocular fixation the patient may have double vision, as the

image which falls on the fovea of the eye that had formerly squinted is now pro?

jected erroneously into space; not only has the false macula acquired correct

projection, but the true macula has lost this one of its special properties. It is

only in young persons in whom false correspondence has not been firmly established by long use that the functions of the true macula can be easily re-established.

Finally, when the squinting eye only is used, monocular double vision may be

experienced though there be no physical abnormality in the refractive media or

in the retina; both the images which fall on the true and on the false maculae excite

perception of the character which normally belongs to the true fovea and both are

projected into space. On attentive fixation the false macula may even be used in

preference to the true one, and the external projection of its image may corre?

spond more accurately with the actual position of the object. But though a point in the retina of one eye outside the macula may develop some of the functions of

the normal fovea and a physiological correspondence with the fovea of the other

eye, owing to the more sparse arrangement of the receptors in the periphery of the

retina its visual acuity cannot attain that of the normal macula. The reduction

of central visual acuity and the erroneous projection of images perceived by it

after a squint has been corrected is a further instance that in certain conditions

even the functions of macular vision may also be modified.

The secondary abnormal correspondence between the macula of one eye and a

point in the periphery of the other retina, and the enhanced function of the latter,

cannot be due to retinal or subcortical processes as in these function is rigidly established and organized; it can only be attributed to functional adaptations in

the cortex. The point which is most intimately connected by anatomical pathways with the false macula of the squinting eye has developed properties which normally

belong to the macular cortex.

All these facts indicate that the organization of function in the visual cortex is

not rigid and determined exclusively and inevitably by impulses that reach each

spot in it from corresponding points in the two retinae, and that its functional

response is modifiable by various conditions; its organization is plastic, as is the

representation of movement in the motor cortex.



358 G. Holmes

The evidence available from clinical observations indicates that in man the

striate area or visual cortex is merely a perceptive centre. It is through it that all

impulses excited by stimulation of the retinae must pass to reach consciousness.

It also provides the physiological basis for the fusion of the two separate images received by it in binocular vision, for it is only at this level that impulses from the

two retinae come together. The perception of colour also depends on the striate cortex; mild lesions of the

cortex which do not abolish perception of light frequently disturb colour vision; there is no evidence that this is subserved by any other region of the brain.

Relative localization, that is localization of objects in space with reference to

the direct Une of vision, which is primarily dependent on the so-called 'local

signs' of the receptive elements of the retina, is also a function of the striate

area; it too may be affected by partial damage of this portion of the cortex

which reduces, but does not abolish, perception.

Recognition of form and discrimination of contour, which depend largely on

relative localization, are also subserved by the calcarine cortex; they too may be

affected by mild cortical lesions which reduce visual acuity. There is no evidence

that they depend on any extra-calcarine connexions. It is a long step in the phylo?

genetic scale from rodents to man, but it is interesting that Lashley (1942) states

that isolation of the striate area by an incision around it, or by destruction of the

rest of the cortex, does not abolish in rats conditioned reactions dependent on

visual impressions. The visual cortex is not, however, concerned in more highly evolved functions

which are developed by the integration of visual with other sensory impressions,

though it provides the raw material on which these work. The identification by vision of familiar objects may be disturbed or abolished by injuries of the lateral

portion of the posterior part of the left hemisphere of the brain, though the

recognition of their form may be preserved. Complete object agnosia is a rare

result of circumscribed lesions; I have not seen it in gunshot wounds, but it has

been described by others. It occurs more frequently with diffuse softenings of

vascular origin which, in many recorded cases, involved both sides of the brain. In

its fully developed form the patient is unable to identify by sight objects, persons or

drawings, though he can recognize them by other sensory impressions, as by touch.

In the identification of objects different sense impressions play a variable role; in some cutaneous and proprioceptive messages take the larger part, in others

visual, and it appears that those in the acquirement of which vision had a pre? dominant part may be affected in a strikingly isolated and specific manner by disease in the immediate neighbourhood of the visual cortex. For instance, a

highly educated man under my observation became suddenly unable to read four

years ago, following a slight stroke. The right halves of his visual fields are restricted, but central vision and vision to his left are unaffected. He is quite unable to

identify by sight or name letters of the alphabet, and cannot learn to do so. This

condition suggested at first an aphasic alexia, but he can write correctly, though



Ferrier Lecture 359

he cannot read what he has written, and can recognize letters by tracing them

and block letters by running his fingers over them. Only visual recognition is

defective. The identification by sight of other objects, even of other visual symbols, as numerals, is undisturbed; he can use figures in calculation and is able to keep his

own accounts. This is an instance of agnosia of letters, or inability to identify by vision symbols in the learning of which vision is predominantly concerned. A few

similar cases have been recorded; in all of these the lesions involved the lateral

and inferior surface of the occipital lobe close to the striate area. In some cases

the damage was limited to the left side, but in a few this region of the brain was

involved on both sides.

Other forms of agnosia result from injuries in the neighbourhood of the visual

cortex. Another man was a competent artist, but since his stroke he has been unable

to use colours and states they had lost their natural significance for him. He is

not colour blind, for he can name most colours and can select them when given their

names, but when tested with Holmgren's wools it was found he was unable to sort

out colours, for example, to select the various shades of red or green. He is,

however, unable to associate colours with familiar objects. When he was asked the

colour of the sky, of grass, or of a rose, his replies, if correct, were based on verbal

associations, not on the association of the colour with the object; colours are for

him no longer properties of objects. This colour agnosia also results from disease of

the lateral surface of the left occipital lobe in the neighbourhood of the visual cortex.

Though relative localization is a function of the striate area, absolute localization

in space, that is of objects seen in relation to self, is an extra-calcarine function

which has developed by the association of visual with other sense impressions,

particularly with those which accompany or result from movement. In my

experience (1919) it is disturbed only by bilateral injuries of the posterior portion of the parietal and the lateral part of the occipital lobes, chiefly by those which

involve the angular gyri, but Best (1917) has found evidence that it may be due to

lesions of the medial surfaces of the hemispheres in the region of the praecuneus and superior parietal gyri. The case of a man in whom the angular gyri were

injured by a rifle bullet that passed through his brain is an instance of spatial

disorientation. He could not take food from his plate or grasp an object in front

of him without groping about for it, as a blind man would, as he was unable to

estimate by vision alone their positions in relation to himself; but he recognized the position of each object at once when he could touch it. In walking through the

ward he collided with large obstacles, as beds and walls, as he could not appreciate their direction or distance from himself. He could not find his way back to his

own bed though he saw it distinctly, or turn his eyes immediately and accurately

to an object in his peripheral vision. Topographical memory was also lost; he was

unable to describe his way in surroundings formerly familiar to him.

When sight is defective owing to damage of either the visual cortex or of the

subcortical visual pathways, objects outside central vision do not excite attention

readily, but visual attention may be seriously influenced by lesions of the brain



360 G. Holmes

outside the striate area which do not affect sight. The most common site of the

causal lesion is at, or in front of, the angular gyrus of either hemisphere. When

disease is unilateral the patient fails to notice objects in the opposite halves of

his fields of vision; if he fixes one of two objects he may not observe that which

lies on the affected side till his attention is drawn to it, and if objects are placed to his right and left he may fail to see one of them. As a result he misses details

in scenes and drawings, and makes errors in enumerating scattered objects.

Though some of these highly evolved associative functions, as the identification

of objects, the recognition of spatial relations and local visual attention, are

subserved by portions of the brain considerable distances from the striate area, it

is on anatomical grounds probable that the visual perceptions subserving them are

elaborated in the cortex surrounding it, for Le Gros Clark (1941) has shown that

no long association tracts leave the striate area, and that impulses from it can

be propagated to distant parts of the brain only by relays of short systems of fibres.

Dusser de Barenne & McCulloch's (1938) investigations by the application of

strychnine to the striate cortex point to the same conclusion, and von Bonin, Garol & McCulloch (1942), by employing the same method, found that electrical

responses do not extend beyond area 18. Connexions of the visual apparatus of

the two hemispheres, by which their activities can be linked up and impressions from the two halves of the visual fields can be integrated, are apparently furnished

by commissural fibres which take origin only in the cortex around the striate area.

According to van Valkenburg (1913) and other anatomists no fibres from the latter

cross through the corpus callosum to the opposite side, but this has been disputed

by Polyak (1932); if they exist they must be few in number. On the other hand

numerous callosal fibres connect the peristriate areas of the two hemispheres of the

brain (Bailey, von Bonin, Garol & McCulloch 1943). These anatomical findings are

confirmed by the observations of von Bonin, Garol & McCulloch (1942) that stimu?

lation of one striate area by strychnine never excites changes in potentials in the

opposite hemisphere, while application of strychnine to the peristriate area 'fires

off' symmetrical foci on the other side.

The cortex around the striate area, probably those parts characterized by special structure and termed by Elliott Smith (1907) peristriate and parastriate areas, and

by Brodmann (1909) areas 18 and 19, may be a sorting house or marshalling yard for visual impressions which in conjunction with other sensory impulses subserve

more highly integrated functions. If it serves this purpose the term ' visuo-psychic',

originally applied to it by Munk (1881) and adopted by Bolton (1900) and Campbell

(1905) is, within a limited meaning, particularly apt. The conclusions that can be drawn from observations on human subjects there?

fore indicate that in man primary visual perception, including colour vision, relative localization in space and perception of form, is subserved by the cortex of the striate area, and that though there is an exact geometric or point-to-point projection of the retina on this area its functional organization is not rigidly determined by this point-to-point representation, but is to some extent plastic



Ferrier Lecture 361

or modifiable. More highly differentiated visual functions, which are developed by the association of visual with other sensory impressions, on the other hand, depend on the integrity of the brain outside the striate area.

References

Adrian, E. D. 1939 Proc. Roy. Soc. B, 126, 433.

Bailey, P., von Bonin, G., Garol, H. & McCulloch, W. S. 1943 J. Neurophysiol. 6, 129. Bartley, S. H. & Bishop, G. H. 1933 Amer. J. Physiol. 103, 159. Best, F. 1917 Archiv. fur Ophthalmologie, 93, 49. Bolton, J. S. 1900 Phil. Trans. B, 193, 165. Brodmann, K. 1909 Vergleichende Lokalisationslehre der Grosshirnrinde. Leipzig. Brouwer, B. 1930 J. Physiol. Neurol. 40, 147. Brouwer, B. & Zeeman, W. P. C. 1926 Brain, 49, 1. Brown, S. & Shafer, E. A. 1888 Phil. Trans. B, 179, 303. Brown, T. G. & Sherrington, C. S. 1912 Proc. Roy. Soc. B, 85, 25.

Campbell, A. W. 1905 Histological Studies on the Localization of Cerebral Functions. Cam? bridge University Press.

Clark, W. E. le Gros 1941 J. Anat., Lond., 75, 225. Clark, W. E. le Gros 1942 Trans. Ophthal. Soc, U.K., 62, 229. Clark, W. E. le Gros & Glees, P. 1941 J. Anat., Lond., 75, 295. Dusser de Barenne, J. G. & McCulloch, W. S. 1938 J. Neurophys. 1, 69. Ferrier, D. 1875 phil. Trans. 165, 433. Ferrier, D. 1876 Function of the Brain. London. Ferrier, D. 1888 Brain, 11, 7. Fritsch, G. & Hitzig, E. 1870 Arch. Anat. Physiol. 37, 300. Fuchs, W. 1920 Z. Psychol. 84, 67. Henschen, S. E. 1890-94 Klinische und Anatomische Beitrage zur Pathologic des Gehirns.

Upsala. Hitzig, G. 1874 Untersuchungen ueber das Gehirn. Berlin. Holmes, G. 1918 Brit. J. Ophthal. 2, 449. Holmes, G. 1919 Brit. med. Journal, 2, 193. Holmes, G. 1931 Brain, 54, 470. Holmes, G. 1934 Jb. Psychiat. Neurol. 51, 39. Holmes, G. & Horrax, G. 1919 Arch. Neurol. and Psychiatr. 1, 385. Holmes, G. & Lister, W. T. 1916 Brain, 39, 34.

Igersheimer 1919 Archiv. fur Ophthalmologie, 100, 357. Kleist, K. 1934 Gehirn Pathologic Leipzig. Lashley, K. S. 1939 J. comp. Neurol. 70, 45.

Lashley, K. S. 1942 Biolog. Symposia, 7, 301. Lorente de N6, R. 1934 J. Physiol. Neurol. 46, 113. McCulloch, W. S. & Dusser de Barenne, J. G. 1940 Amer. J. Physiol. 129, 421. Marshall, W. H. & Talbot, S. A. 1942 Biolog. Symposia, 7, 117. Minkowski, M. 1920 Schweiz. Arch. Neurol. Psychiat. 6, 201. Minkowski, M. 1939 Schweiz. med. Wschr. 69, 67. Munk, H. 1881 Ueber die Funktionen der Grosshirnrinde Berlin.

Polyak, S. 1932 The Main Afferent Fibre Systems of the Cerebral Cortex in Primates. Univ. California Press, 14, 370.

Polyak, S. 1933 J. comp. Neurol. 57, 541. Shafer, E. A. 1888 Brain, 11, 1. Shafer, E. A. 1888 Brain, 11, 145. Smith, G. Elliot 1907 J. Anat., Lond., 41, 237. Talbot, S. A. & Marshall, W. H. 1941 Amer. J. Ophthal. 24, 1255. van Valkenburg, C. T. 1913 Brain, 36, 119. von Bonin, G., Garol, H. W. & McCulloch, W. S. 1942 Biolog. Symposia, 7, 165.



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Ferrier Lecture: The Organization of the Visual Cortex in Man