Neumpwchologi~ Vol. 16, pp. 697 to 708. Pergamon Press Ltd. 1978. Printed in Great

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Bntam

WITHIN THE HEMIANOPIC FIELD VISUAL FiJN&ION FOLLOWING EARLY CEREBRAL HEMIDECORTICATION IN MAN - II. PATTERN DISCRIMINATION M. T. B’RRENIN Laboratoire

de Neuropsychologie Expkrimentale, INSERM, 16 avenue Doyen L&pine, 69500 Bron, France (Received

Unite 94,

28 April 1978)

Abstract-The ability for discriminating large, simple patterns within the hemianopic field has been tested in six subjects hemidecorticated in early life for infantile hemiplegia-epilepsia, and seen in a previous study to have preserved localization capacities within this hemifield. Controls of the experimental procedure were done in two other Ss with a pregeniculate (chiasmatic) lesion. In hemidecorticated Ss. the cumulative score, across all sessions, exceeded the chance level in two Ss. The same was observed when all the scores of the 6 Ss were cumulated. This was not so in control Ss. Thus, coarse pattern discrimination could also be subserved in parts of the visual fields no longer controlled by cortical areas. These results are discussed regarding animal lesions experiments.

CONTRASTING with what is currently admitted in the neurological literature, we found in a previous study [l], that early cerebral hemidecortication in man does not lead to a complete hemianopia. Instead, some spatial localization abilities were seen to be preserved in the “perimetrically blind” hemifield of six hemidecorticated subjects who were still able to estimate the position of a visual target in this hemifield, either by pointing with the hand or by directing the eyes to it. Such residual vision had been first demonstrated in adult patients with more localized cortical lesions [24]. In a single case with an occipital lobectomy, sparing probably a small remnant of striate and part of prestriate cortex, WEISKRANTZet al. [3] observed that residual vision in the hemianopic field also included pattern discrimination. According to animal studies [5] visual discrimination capacities should be greatly reduced when occipital resection includes, besides striate cortex, the whole areas 18 and 19. Thus, in hemidecorticated Ss, pattern discrimination in the hemianopic field should presumably be lacking, unless factors such as precocity of the lesion could have allowed greater recovery of visual function. This was tested in the six hemidecorticated patients already examined for spatial localization.

SUBJECTS The six Ss had a similar history of infantile hemiplegia-epilepsia. Most of them had been operated on between 6 and 9.5 yr, and one (DR) at the age of 17 yr. Hemidecortication was performed on the right side in four cases (JBF, DR, MV, CC) and on the left side in two cases (CL and CB). Other clinical details can be found in the first part of this study [I] and are summarized in Table 1. 697

698

M. T. P~RENIN Table 1.

Subiects Sex Aetioloaical data CL M Obstetrical injury and neonatal anoxia M &urge-Weber disease JBF DR

F Sturge-Weber

CB MV

F Neonatal,anoxia F Congenital right hemisphere malformation : frontal and temporal porencephahc cysts. First operation at the age of 2 (removal of the cysts and temporal Iobectomy) F Prematurity of 1.5 month. Toxicosis at 14 months

cc Cl c2

disease

M A similar history of anterior frontal traumatism and fracture with M Extended wound of the duramater up to the turcic sella and with chiasmatic lesion

Onset of neurological symptoms 11 months 9 months 13 months 3.5 yr 7 months

3 yr

Age at and side of hemidecor& cation (yr) 7, left

Age at testing (yr) 19

9, right

17

4s

40

43

17, right

20

65

60

61

6, left 7, right

19 9

78 7s

14 83

7s 77

a/10 8/10

4110 4110

9.S right

18

68

69

65

4110

7110

4110

l/l0

31 yr

32

16.5 yr

18

Two Ss (C, and CZ) with pregeniculate leaions (traumatism controls of our findings on the hemidecorticated Ss.

IQ at the time of testing Verbal Perform Glob 79 77 7s

Visual acuity Right Left eye eye 10&o 9/lO l/l0

s/10

lO/lO lo/lo

lo/lo

lo/lo

of the optic chiasm), were also tested as

METHODS Ss had to solve two-discriminanda problems in the following experimental conditions: A white tangent screen, which could be. uniformly illuminated at high or low mesopic levels (respectively at 7.5 and 0.02 cd/m3 served as a background for the visual targets. Series of pairs of visual patterns were provided by a Kodak “Carousel” projector placed behind the subject. Each pattern of a pair was projected singly in a random order (according to Gellermann schedules) into the inferior part of the hemianopic field, so that the stimuli did not encroach the blindspot area. Different pairs of simple patterns were used (see Fig. 1): triangles/disks (a, b, c), triangles/circles (d), horizontal/vertical lines (e), double small disks, horizontally or vertically aligned (f). For each pair, the two stimuli were equalized in total luminous flux, and also in contour length for stimuli d, e, f. The size of the stimuli and their distance from the vertical meridian could be altered by means of a variable focus lens and by displacing the projector. Exposure duration was limited to So0 or 100 msec by an electronic shutter. Most often bright patterns on a darker background were used, but at least one session with dark patterns on a brighter background was also carried out for each S. Stimulus background contrast varied from session to session in the range of O.S/l, to 700/l, according to the patterns projected and to the background luminance. But in all sessions, i.e. whatever the pattern pair and the distance from the vertical meridian chosen, luminance change caused at the center of the screen by either stimulus of each given pair was the same (for measurements methods see [l]). During the tests, the S was sitting at 57 cm in front of the screen, the head maintained with a chin and forehead rest. He was required on each trial to fixate a small electroluminescent diode at the center of the screen. Fixation was visually monitored through a peephole, just above the tixation diode. After each stimulus presentation, the S had to report verbally, in a forced choice condition, which pattern of the pair

PATTERN DtSCRlMQWTlOK

699

b A

FIG. 1. Pairs of patterns projected in the hemianopic field of the 6 hemidecorticated and the 2 control Ss. a, b, c, f, patterns equated in area, d, e and f patterns equated in contour length. Patterns of pair e are equated with patterns of pair f for total luminous flux. tested had been projected. Before each session, the S was made familiar with both patterns, as he was allowed to direct the eyes to the stimulated area. One session of 40 trials (20 for each stimulus of one pair) was carried out for each experimental condition. Eccentricity, contrast, exposure duration and size’of the targets were varied from session to session mainly for the triangle/circle pair. Most types of stimuli were used for each S, although the totality of the 13 sessions could not be performed in all of them. because of the difficulty to keep steady eye fixation and to cooperate in the task for a suEciently long time. All the tests were done binocularly except in the two control subjects with bitemporal hemianopia, who had one eye covered.

RESULTS (a) Subjective reports When a pattern was flashed, Ss of both groups could perceive light spreading into the normal part of their field, however, they did not give the same verbal report: control Ss only reported having seen a very dim light arising from the middle part of the screen, whereas hemidecorticated Ss felt a rather bright light arising from their impaired visual field. But none of the Ss could “see” the form of the pattern, which they had to “guess” when required to respond in the tests. In some cases, however, hemidecorticated Ss reported that successive presentations in a given session did not appear to be the same, but that something “sharp”, or “round” seemed to appear in the bright light, when triangle/ circle pairs were presented, or that more or less light was present near the midline when horizontal/vertical patterns were used. This could not be ascribed to a different amount of light spreading to the center of the screen, as we already mentioned that no huninance difference was detected at this point, whatever pattern of a given pair being projected. Occasionally Ss could really see the form of the target, but each time they pointed this out, as required, a shift of the gaze toward the hemianopic field could be observed through the peephole. These trials were rejected and replaced by others.

700

M. T.‘WRENIN”~~-’

(b) Performances to the tests As seen in Table 2, individual scores generally did not reach high values, but were mostly distributed near the chance range (estimated from 15 to 25/40 for individual sessions). Table 2. Subjects

CL JBF DR CB MV CC Ct C1 Sessions

(a) (a) (a) 16119 16/19 l6/19 100 100 500 78 730 78 20 26. 19 21 16 25 27. 21 ; E 20 17 20 19 22 18 1

19 18 2

16 17 3

(a) 16/19 500 730

(a) 8/11 100 78 30*

Type of stimulus (a) (a) (a) 8/11 8/11 8/11 100 500 500 730 78 730 33’

(b) 8/11 100 0.5

24 22

:“3 18

21 21 27. 19

19

z 21 19 21 14

16 18 6

20 19 7

20 20 8

19 19 9

::

220”

19

E 16

19 18 4

19 17 5

24

(c) 9/11 100 60 31*

(d) 819 100 39 21

(e) 8137 100 39 35*

:s” 25 24 18

:: 19 21 16

17 24 10

18 14 11

cozct per subject

:: 25 I;’

$?7 100 31 33* 17 27+ 16 24

17 18 12

18 17 13

46 45

71.6” 51.6 54 49.4 57.2+ 45

For each stimulation are indicated from above to below: the type of patterns (“a”, “b”, “c” etc. see Fig. 1 for corresponding shape and size), the distance from the vertical meridian, in degrees, the exposure duration in msec; and the pattern/background contrast. The values in the table represent the number of correct responses in 40 trial sessions. The percentages of correct responses are given for each S in the last right column. *Indicates values above the chance level at P O.OS-confidence level.

However, when the cumulative score (i.e. the sum of values obtained in individual sessions) was considered, it exceeded the chance level in the hemidecorticated group whereas it did not in the control group. Statistical analyses are done by means of comparisons of the observed scores to a theoretical frequency, in application to Laplace-Gauss (0.1) law. The positive results obtained in hemidecorticated Ss group seem in fact to be due to the higher scores in two of them (CL and MV), and especially to those of CL. By using the same statistical estimation as above, but for the cumulative score of each S, CL and MV are the only two Ss who gave a number of correct responses above chance level. If we consider individual sessions, CL performed specially well, as he exceeded the critical score of 25/40 in T out.of the 9 sessions he performed. MV did so in only one session among 11. Various conditions of stimulation were used for each S in order to check if either the type of pattern (e.g. presented as an homogeneous area or as an outline), or the stimulus parameters (such as location, size, contrast, duration) for a given pair of patterns could influence the scores. Results reported below were obtained by using comparison of two observed frequencies (i.e. two cumulative scores) in application of Laplace-Gauss (0.1) law. Cc) Influence qf’ the type of patterns When hemidecorticated patients had to discriminate between triangles and circles, the cumulative score of CL and MV was higher when the patterns were presented as bright areas (session 5) than as outlines (session 11). The same was true for the cumulative score of all hemidecorticated Ss. However, in both cases. this difference failed to reach a significant level. When horizontal and vertical patterns had to be discriminated, the cumulative score of CL and MV was quite unchanged when outlines (thin lines. session 12) were replaced by

PATTERN DISCRIMINATION

701

homogeneous areas (double small disks, session 13) of the same total flux. Cumulative score of all hemidecorticated Ss slightly decreased from one of these sessions to the other. The difference was far from significance in the two cases. (d) InjZuence of stimulus parameters For the triangle/disk pair, eccentricity (i.e. distance from the vertical meridian), contrast, duration of exposure or size were systematically varied in different sessions for each S. Influence of these parameters on the scores of hemidecorticated Ss are summarized below. Eccentricit),

Approaching the stimuli from the vertical meridian significantly improved the cumulative score of CL and MV (Fig. 2a). When cumulative scores of all hemidecorticated Ss are considered, improvement was also observed, although it did not reach a significant level (Fig. 3a).

a -ECCENTRICITY

b-CONTRAST

c-

DURATION

d-SIZE

40

30

20

10

Ro. 2. Cumulative scores (percentages of correct responses) in two hemidecorticated Ss (CL and MV) for triangles/disks discrimination within the hemianopic field. Only response; to pair “a” are considered, except in the 3rd and 5th black columns (see below). (a) Effect of varying the eccentricity of the patterns. Results for two different exposure times (100 a?d 500 m&c) and two different contrasts (78 and 730) are cumulated. White bar: triangles and disks resnectivelv at 16”/19” from the vertical meridian. Black bar: So/11”. Difference between the two &er&es is &niiicant at P co.01 (normal deviate “U” =’ 2.84). Significance level from BEYER’S [41] tables. (b) Effect of changing the pattern/background contrast. Results for two different exposure times (100 and 500 msec) and two different distances (16”/19” and 8’/11”) are cumulated. I: increase of pattern/background contrast from 78 (white bar) to 730 (black bar). Difference between the two percentages U = 1.15 (N.S.). R = reversal of pattern/ background contrast from 78 (white bar: nair “a”) to 0.5 (black bar: pair “b” of Fig. 1). Difference between the two percentages: U = 0.66 (N.S.). (c) Effect of-change in exposure duration. Results for two different distances (16”/19” and 8”/11”) and the same contrast (78) are cumulated. Only MV’ scores are considered. White bar: 100 msec exposure, black bar: 500 msec. Difference between the two nercentages: U = 0.3 (N.S.). (d) Effect of moderate change in triangles and disks size. White-bar: pas “a”, black bar: pa& “c” of Fig. 1. Distances from the vertical meridian are respectively 8’/11” and 9”/11”. Exposure duration = 100 msec. Contrast: 78. Difference between the two percentages: U = 0.17 (N.S.).

M. T. PeReNM

c -DURATION

b-CONTRAST

a-ECCENTRICITY

d -SIZE

r i

:

1

L

Fm. 3. Cumulative scores (percentages of correct responses) of the 6 hemidecorticated Ss (whz&azd black bars) and of the two control Ss (dotted and striped bars) for triangles/ ’ rimination, within the hemianopic field. Only responses to pair “a” are considered, except in the 3rd and 5th black and striped columns (see below). (a) Effect of varying the eccentricity of the patterns. White and dotted bars: triangles and disks respectively at 16’/19” from the vertical meridian. Black and striped bars: 8”jll”. Difference between percentages which are represented by white and black bars (i.e. hemidecorticated Ss): U = 1.06 (N.S.). (b) Effect of change in pattern/background contrast. I: increase of contrast from 78 (white and dotted bars) to 730 (black and striped bars). Difference between percentages represented by white and dark bars is sign&ant at P ~0.05 (U = 2). R: reversal of contrast from 78 (white and dotted bars: pair “a”) to 0.5 (black and striped bars: pair “b” of Fig. 1). Difference between percentages represented by white and dark bars: U = 0.56 (N.S.). (c) Effect of change in exposure duration. White and dotted bars: 100 msec exposure, black and striped bars: 500 msec. Difference between percentage represented by white and dark bars is significant at P CO.01 (U = 2.84). (d) Effect of moderate change in triangles and disks size. White and dotted bars: pair “a”, black and striped bars: pair “c” of Fig. 1. DifTerence between the percentages represented by white and dark bars: U = 0.35 (N.S.).

Contrast. The stimulus/background contrast was varied, by decreasing either the background or the target luminance. When the background luminance was lowered from 7.5 to 0.02 cd/m2 and that of the target remained unchanged, i.e. when the target/background contrast increased, the cumulated score of CL and MV improved, although not until significance (Fig. 2b). For the cumulated score of all hemidecorticated Ss, improvement was more marked and statistically significant (Fig. 3b).

When the stimulus/background contrast was reversed by projecting dark patterns on a high mesopic background, almost no difference was observed in the cumulative scores of CL and MV nor of all hemidecorticated Ss, (Fig. 2c, 3~). Duration of exposure. Increasing exposure time from 100 to 500 msec only slightly improved the cumulative score of MV (Fig. 2d). Gaze fixation instability did not allow CL to correctly perform the 500 msec exposure tests. For all hemidecorticated Ss the cumulative score significantly improved by increasing exposure time. Size. Moderate increase of the size of the patterns did not lead to noticeable variation of the cumulative scores of CL and MV nor of all hemidecorticated Ss (Figs. 2d and 3d).

PATTERh

DISCRIhlIJ-+ATlOh

703

DISCUSSIOK Although this \+as beyond any doubt in only two Ss, the results reported here indicate that the ability to discriminate simple patterns in a perimetrically blind fie!d may be preserved in hemidecorticated patients. An obvious objection, however, is that such discrimination could be due to light spreading into the normal field, or directly through the intra-ocular media on the hemi-retinae connected with the intact hemisphere. In fact, this possibility was ruled out by different controls : (1) Diffusion of light from either pattern of the pairs used in this study, to the center of the screen was the same. (2) Although tested exactly in the same way as hemidecorticated Ss, the two Ss with pregeniculate lesion failed to perform above the chance level. (3) Reversing the target/background contrast (for the triangle/disk pair) did not impair significantly the performances. Alternatively some instability of gaze, present in at least half of the Ss, could have facilitated transitory shift of the eyes to the hemianopic side. But eye fixation was carefully monitored throughout the tests, allowing rejection of trials where the eyes had moved from the central fixation position. Moreover, in sessions where the exposure time was below the saccadic reaction time, the cumulative scores of all Ss, or of CL and MV still remained above the chance level. Thus, residual vision in areas of the field devoid or cortical control could not only allow to localize visual targets, as demonstrated previously in the same Ss, but also, though in fewer cases, to discriminate simple patterns or lines with different orientations. This ability was also observed by WEISKRANTZ et al. [3] in one adult patient with an hemianopia due to a lesion restricted to striate and part of prestriate cortex. However, it was not present in the six adult Ss that we had examined, although less extensively, and the lesion of which probably included important part of the secondary visual area [4]. The same mechanism of “residual vision” had been put forward to explain the completion of symmetrical patterns presented across the blind area in patients with cortical lesions [6-71. In contrast to visual targets localization, the criterion for pattern discrimination in the hernianopic field could not be fulfilled by all of the hemidecorticated Ss but only by CL and MV. These two Ss were also those who performed best in the localization tests. Such interindividual differences do not seem to be explained either by the side of the hemidecortication or by the time elapsed between the lesion and the tests, but probably in part by the age at the time of the lesion (see discussion in [l]). This latter factor could also possibly account for the negative results obtained with adult patients [4]. In addition, we felt that, although their intellectual level was not much higher compared to the others. Ss CL and MV cooperated better and paid much more attention in the tests. Comparison of the responses in the various conditions allows to raise some hypothesis concerning the strategies these 2 Ss could use for discriminating visual pattern within their hemianopic field. Although they performed almost as well for outlines as for filled shapes, this does not imply that they really did so on the basis of contour orientation. Indeed, scores did not significantly decrease from session 12 to session 13, i.e. when the small disks pairs replaced the horizontal/vertical lines. As the cumulative scores improved by increasing stimulus/background contrast or exposure duration, a more important cue could be the regional differences in luminous flux between two stimuli of one pair. This

704

M. T. PERENIN

factor seems to rely mostly on the part of the stimulus which is closer to the vertical meridian as decreasing the distance of the patterns from the vertical meridian improved the scores. in addition CL did not perform above chance level in an additional session where he had to choose between right angle triangle and rectangle, the orientation and size of which minimized local flux differences on the side next to the vertical meridian. In fact, even in normal conditions, spatial distribution of luminous flux should provide an important alternative cue for pattern discrimination besides contour orientation or fine features. In this respect, results by WINANS [8] in the cat suggest that it could be the main factor for differentiating simple patterns, as normal animals do not perform significantly better in such tasks than visually decorticated ones. However, a prevalent role in visual forms discrimination is generally ascribed to the geniculostriate system in mammals, whereas the phylogenetically older retinocollicular pathway is mainly thought to subserve detection and localization of peripheral visual events (according to the “two visual systems” hypothesis [9, lo].) More specifically, in the monkey, total removal of striate cortex does not result in homogeneous deficit of all visual capacities. Soon after the lesion signs of visually oriented behavior are shown by such animals. They progressively recover a close to normal visual guidance, although they remain unable to recognize objects [ll-131. This does not mean however that destriated monkeys have definitively lost all discriminative capacities. They may become able again to detect small differences in size or brightness [14] and classify visual stimuli according to their relative detectability or “salience” [ 121.They can also learn to discriminate luminous flux equated figures differing in total contour length [15]. But discrimination hardly gets beyond such rather primitive attributes of visual stimuli, as according to SCHILDERet al. [16] pure simple pattern discrimination (triangle/circle, equated in flux, area, contour length) can only succeed after a considerable number of trials. The peculiar nature of residual extrastriate vision can be better understood by considering the following facts. Long standing occipital lesions have been shown, by histological observations or in man by fundoscopic examinations, to result in trans-synaptic retrograde degeneration of optic nerve fibers and retinal ganglion cells layer [17-l 91. More interestingly. COWEY[20] observed, in a monkey bilaterally destriated 8 yr before, an atrophy of about 80% of the ganglion cells within a 10’ zone around the fovea, so that the whole ganglion cell layer resembled that of a normal peripheral retina. This suggests that cone information is no longer available to the destriated monkey, as confirmed by the psychophysical results of LEPOREet al. [42]. These authors found that, after total removal of striate cortex in monkey, the spectral sensitivity curve was still normal when tested under scotopic conditions whereas completely displaced towards the scotopic range when tested under photopic conditions. Thus it is not surprising that destriated monkeys can hardly recognize visual forms per se through a completely “peripheral” retina. Nevertheless, this does not imply that after total removal of area 17, as well as in far peripheral visual field in normal conditions, it would no longer be possible to use some characteristics of visual patterns, as cues for a coarse discrimination. As proposed by WEISKRANTZ[21], this would be primarily limited by a comparably poor visual acuity. In fact, numerous other lesions experiments have stressed the role of extrastriate areas in pattern discrimination, although rather important disagreement is found among them and pure discriminative deficits, in which we are much concerned in this discussion, less often encountered. The prestriate and inferotemporal cortex are known to be also involved, through dif-

PATTERN

DISCRIh4lXATIOS

705

ferent ~vays, in this function. Schematically, the more rostra1 the lesions of these cortical areas. the less sensory and more mnemonic (i.e. related to retention. ability to learn .) the resulting deficits. The consequences of bilateral ablation of prestriate cortex on patterns or objects discrimination in monkeys should range from virtual lack of effects [22-241 to important deficits in retention or acquisition of new discriminations [25-281. According to MISHKIN [26] this would mainly depend on the rostra1 extend of the lesion. Bilateral inferotemporal removal has been seen instead to constantly impair both the retention of pattern discrimination acquired prior to the surgery and the acquisition of new visual discrimination following the lesion (see reviews in [26, 291). However, as observed by ETTLINGERet al. [22] and GROSS [29], the deficits are not absolute since most of the discrimination problems can still be solved after prolonged learning. Thus, each visual cortical area seems individually rather dispensible for pattern discrimination. However, although there are very few experimental data concerning the effects of more extensive cortical ablations on visual capacities, those effects tend to be more marked and durable. Monkeys with large bilateral lobectomy, including striate and most of prestriate cortex should have lost the ability for discrimination other than based on total luminous flux [5]. Besides, after combined inferotemporal and prestriate cortex removal, monkeys could not reacquire pattern discrimination after more than 2000 trials [22]. As no cortical lesion experiment allows direct comparison with our results in man, there is evidence that subcortical visual structures are also involved at some stage of visual form discrimination. In fact higher visual functions like form discrimination do not only result, as mainly suggested by MISHKIN’S [26] experiments, from serial hierarchical processing originating in the geniculo-striate system and spreading from there to prestriate and then inferotemporal cortex. Instead visual input should also be processed rather separately in “parallel” visual pathways (besides the geniculostriate system, mainly those relaying either in superior colliculus and pulvinar or in pretectum and pulvinar) through important interactions between the cortical and subcortical part of each pathway [23, 301. Participation of subcortical structures in complex visual functions has been put forward by recent lesions experiments. Monkeys with pulvinar lesions succeed in acquiring a visual pattern discrimination under standard testing conditions, with no limitation of the viewing time [31, 261. However, they fail to learn the discrimination when the stimuli are flashed very briefly [32]. Accordingly, prolonged gaze fixations of the patterns during conventional training should provide compensation for an otherwise undetectable processing deficit [33]. At the midbrain level, mild to severe impairment in pattern discrimination learning has been observed in monkeys [34-371 and cats [38, 391 according to whether the lesions were restricted to the superior colliculi or also invaded the pretectum. In the monkey, pattern discrimination impairments have been also reported with pretectal damage alone [40]. In hemidecorticated Ss, where the lateral genioulate body and also the pulvinar are known to degenerate (see discussion in [l]), the superior colliculus and pretectum possibly represent the anatomical substrate for some residual capacity to discriminate large, highly contrasted patterns. The fact that it was observed in only a minority of cases whereas localization capacity was a constant finding in these Ss agrees with the numerous and convergent evidences that midbrain structures and more specifically the superior colliculus play a primordial role in visual detection and localization but probably only an auxiliary and indirect role in visual form discrimination,

706

M. T. PERENIN

Acknowledgement-We

he has operated the man&ript.

thank Dr. C. LAPRA~for allowing us to investigate the visual capacity of patients on. We are also grateful to M. JEANNERODand F. MICHEL for comments and advice on

REFERENCES 1. PERENIN,M. T. and JEANNEROD,IM. Visual function within the hemianopic field following early cerebral hemidecortication in man-I. Spatial localization. Neuropsychologia. 16, 1-13, 1978. 2. POEPPEL,E., HELD, R. and FROST, D. Residual visual function after brain wounds involving the central visual pathways in man. Nature, Lond. 243, 295-296, 1973. 3. WEISKRAMZ, L., WARRPIGTON,E. K., SANDERS,M. D. and MARSHALL,J. Visual capacity in the hernianopic field following a restricted occipital ablation. Brain 97, 709-728, 1974. _ 4. PERENIN,M. T. and JEANNEROD.M. Residual vision in cortically blind hemifields. Neuroosvcholoaia . . _ 13, 1-7, -1975. 5. PASIK. T. and PASIK, P. The visual world of monkeys deprived of striate cortex: effective stimulus parameters and the importance of the accessory optic system. Vision Res. Suppf. 3, 419435, 1971. 6. BENDER, M. B. and TEUBER, H. L. Phenomena of fluctuation, extinction and completion in visual perception. Archs Neurol. Psychiat. 15, 627-659, 1946. T. Residual function in cortically blind hemifields. &and. J. Psycho/. 17, 320-322, 1976. 1. TORJIJSSEN, 8. WINANS,S. S. Visual cues used by normal and visual decorticated cats to discriminate figures of equal luminous flux. J. camp. physiol. Psycho/. 74, 167-178, 1971. C. B. Two mechanisms of vision in primates. Psychot. Forsch. 31, 299-337, 1968. 9. TREVARTHEN, 10. SCHNEIDER,G. E. Two visual systems. Science, N. Y. 163, 895-902, 1969. 11. HUMPHREY,N. K. and WEISKRANTZ,L. Vision in monkeys after removal of the striate cortex. Nature, Lond. 215, 595-597,

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12. HUMPHREY,N. K. What the frog’s eye tells the monkey’s brain. Brain Behav. Evol. 3, 324-337, 1970. 1974. 13. HUMPHREY,N. K. Vision in a monkey without striate cortex: a case study. Perception 3,241-255, vision in the monkey: discrimination of 14. PASIK, P., PASIK,T. and SCHILDER,P. Extrageniculostriate luminous flux equated figures. Expl Neurol. 24,421-437, 1969. 15. WEISKRANTZ.L. Contour discrimination in a _ youna_ monkev with striate cortex ablation. Neuropsvcho_. Iogia 1, 145-i64.1963. 16. SCHILDER,P., Pm, P. and PASIK, T. Extrageniculostriate vision in the monkey-III. Circle vs triangle and “red vs green” discrimination. E~pl Brain Res. 14. 43-8, 1972. 17. VAN BUREN, J. M. The retinal ganglion cell layer. 2 Physioiogicai-Anatomical Correlation in Man and Primates of the Normal Topographical Anatomy of the Retinal Ganglion CeN Layer and its AIterations with Lesions of the Visual Pathways. Charles C. Thomas, Springfield, Illinois, 1963. 18. VAN BUREN, J. M. Tram-synaptic retrograde degeneration in the visual system of primates. J. Neural. Neurosurg. Psychiat.26, 402409, 1963. E. N., BEHRENS,M: IM. and ECKLEHOFF,R. J. Homonymous hemiopic 19. HOYT, W. F., RIO+MONTENEGRO,

hypoplasia. Fundoscopic features in standard and red-free illumination in three patients with congenital hemiplegia. Br. J. Ophthai. 56, 537-545, 1972. 20. COWEY, A. Atrophy of retinal ganglion cells after removal of striate cortex in a rhesus monkey. Perception 3, 257-260,

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h4. T. PEREMS

Deutschsprachige Zusammenfassung: Die FBhigkeit, grol3eeinfache Muster innerhalb des hemianopischen Gesichtsfeldes zu unterscheiden, wurde bei 6 Personen untersucht, welche in friihemLebensalter wegen infantiler Hemiplegie-Epilepsie hemidecorticiert wurden. In einer friiherenStudie hatte man bei diesen Probanden gefunden, daR sie die Fshigkeit innerhalb des Halbfeldes zu lokalisieren bewahrt hatten. Kontrolien des experimentellen Vorgehens wurden bei 2 anderen Personen mit Lgsionen vor dem Geniculatum (im Bereich des Chiasmas) durchgefiihrt. Bei dem hemidecorticierten Probanden waren die iiberalle Experimente kumulierten Werte iibertufallig.Dies galt such , wenn alle Range der 6 Versuchspersonen kumuliert wurden, jedoch nicht bei den Kontrollpersonen. Eine grobe Musterdiskriminlerung konnte also such in jenen Teilen des Gesichtsfeldes erfolgen, die nicht linger von Rindenbezirken kontrolliert wurden. Die Resultate wurden im Hlnblick auf die Ergebnisse von Tierversuchen diskutiert.

Visual function within the hemianopic field following early cerebral hemidecortication in man--II. Pattern discrimination.

Neumpwchologi~ Vol. 16, pp. 697 to 708. Pergamon Press Ltd. 1978. Printed in Great ,F Bntam WITHIN THE HEMIANOPIC FIELD VISUAL FiJN&ION FOLLOWING E...
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