RECOGNITION OF RANDOM SHAPES IN UNILATERAL BRAIN DAMAGED PATIENTS: A REAPPRAISAL 1 Edoardo Bisiach, Paolo Nichelli and Claudio Sala (Centro di Neuropsicologia dell'Universita di Milano and Oinica Neurologica dell'Universita di Modena)

In earlier studies concerning the role of the side of the lesion in visuoperceptual disorders following brain damage, different critical factors were suggested as responsible for the defective performances observed in the various brain-damaged subgroups. Meier and French (1965) claimed that the complexity of the pattern produces poor performance in patients with right temporal lobectomy. The same hypothesis was put forward by De Renzi and Spinnler ( 1966) to explain the failure of right brain-damaged patients on Street's completion test and on Poppelreuter's mixed figure test, while both Kimura ( 1963) and Milner ( 196 7) suggested that familiarity and degree of verbal codability improve the recognition of a given pattern after right temporal excision. However, a recent attempt to verify these hypotheses empirically did not provide supporting results. Bisiach and Faglioni (1974), using a task requiring the recognition of meaningless patterns (the random shapes generated by Vanderplas and Garvin, 1959), found that high complexity and low verbal associative value produced greater impairment in left than in right braindamaged patients. Conflicting results have been obtained in a number of experimental studies employing the same kind of patterns in a lateral field tachistoscopic exposure paradigm. Fontenot (1973) and Hellige and Cox (1976) found a significant left visual field advantage when high complexity (12-point) random shapes had to be selected from multiple choice visual displays. Hines ( 1978) stressed the "complex nature" of tachistoscopic recognition of random shapes, while analyzing his failure to confirm the same kind of asymmetry with an experimental paradigm which employed verbal and non-verbal competing tasks to insure fixation. Dee and Fontenot .( 1973) and Hatta ( 1976, Experiment II) using a "same or different" judgment paradigm found a left 1

This research was supported by CNR grant n. 75.00487.04.

Cortex (1979) 15, 491-499.

492

E. Bisiach, P. Nichelli and C. Sala

visual field superiority only when patterns had to be recognized after a time delay, but Hannay, Rogers and Durant (1976), with a similar experimental procedure, found a right visual field advantage for delayed recognition of the same patterns. More recently, however, Endo, Shimizu and Hori (1978), using a "go-no go" procedure, found reaction time shorter for left visual field presentation of 12-point random shapes, thus confirming a right hemisphere superiority. As these discrepancies demonstrate, hemispheric asymmetry for these kinds of recognition tasks is likely to be related not only to stimulus features, but also to other experimental variables such as exposure time and the composition of multiple choice displays. It may be hypothesized for instance, that, since defective exploration of the visual display has been shown in severe Wernicke aphasics by Tyrer (1969), the poor performance in random shapes recognition found in left brain-damaged patients by Bisiach and Faglioni ( 197 4) is contingent upon the high number of distracting patterns in the multiple choice display. On the other hand, high similarity among alternatives may represent a major problem for right brain-damaged patients, if one accepts the view of De Renzi, Scotti and Spinnler (1969) that these patients are impaired when the recognition task involves subtle visual discriminations. In this study two experiments on random shapes recognition were carried out in brain-damaged patients. In the first experiment the number of alternatives and their degree of similarity in the multiple choice display were varied, and in the second experiment the stimulus was presented for two different exposure times. The main aim of the research was to assess the relevance of these factors to the shapes recognition impairment of patients with damage to either hemisphere.

ExPERIMENT

I

Materials and Method Subjects

Thirty-four right-handed control subjects (C) and 101 right-handed patients with unilateral brain lesion (BD) were examined. The only basis for the exclusion of a patient from the study was physical inability, mental confusion, or aphasia so severe as to prevent comprehension of the test instructions. The number of excluded patients was found not to be significantly different among the braindamaged· groups. BD patients were subdivided according to the side of the lesion and to presence/absence of visual field defect (VFD), assessed by confrontation and supplemented by double simultaneous stimulation in any apparently negative case (Bisiach and Faglioni, 1974 ). The left hemisphere group included 57 patients, 32 without (L-) and 25 with VFD (L+ ); the right hemisphere group included 44 patients, 20 without (R-) and 24 with VDF (R+ ).

Recognition of random shapes

493

Stimuli

Stimuli were 32 5 X 5 em black patterns, printed on a white background (Figure 1 ). They were chosen from among 120 progressive distortions generated by means of a fish-eye optical device from eight 24-point random shanes (Bisiach, Capitani and Spinnler, 1976).

• • • • • •-A • • • e e •r' •{') •() *

~

*

*

*

ji *

~



*"

*

~

*

*

*

*

*

•, *

~

•() *

*

Fig. 1 - Shapes used in the two recognition tasks. Patterns marked with an asterisk were the stimuli to be recognized in Experiment I and the whole set of stimuli in Experiment II.

Sixteen out of the 32 patterns (those marked with an asterisk in Figure 1) were separately printed on 6 X 6 em white cards and constituted the set of stimuli to be recognized. Twenty multiple choice displays were prepared, each containing 4 or 8 random shapes arranged in a single vertical column, and the displays were presented in the following testing conditions: (1) 4 alternatives -low similarity (41): 8 multiplechoice displays corresponding to the upper and lower halves of the columns of Figure 1.

E. Bisiach, P. Nichelli and C. Sala

494

(2) 8 alternatives -low similarity (8L): 4 multiple choice displays corresponding to columns of Figure 1. (3) 4 alternatives - high similarity: 8 multiple choice displays corresponding to the rows of Figure 1.

Procedure The subject was seated at a table in front of the examiner. Instructions were given verbally and by gestures and repeated until the examiner was sure that the subject had understood a preliminary task carried out with a different set of random shapes. The stimulus was placed on the table at a reading distance for 5 sec. and then removed; immediately afterwards, recognition of the stimulus was tested on the apprppriate multiple choice display. An error was scored whenever a mismatch occurred or a time of 30 sec. had elapsed without any response. Each of the 16 stimuli was shown three times during the test, one for each of the three conditions of the test. Therefore the subject had to perform 48 recognitions. The maximum possible error score for each of the three conditions was 16. Stimuli and testing conditions were randomly alternated according to a fixed schedule with the constraint that the same pattern and the same multiple choice display should not be immediately readministered.

Results

The mean recognition errors (adjusted for age and educational level) of the 5 experimental groups in the 3 conditions are given in Table I. TABLE I

Mean Recognition Errors (Adjusted for Age and Years of Schooling) of the 5 Experimental Groups in the 3 Subtests

4L 8L 4H Legend:

4L 8L 4H

c

L--

L+

R-

R+

0.6 1.9 5.0

1.7 4.5 7.1

3.0 5.4 7.3

1.9 3.5 6.1

2.0 4.5 6.6

= 4 alternatives = 8 alternatives = 4 alternatives -

low similarity; low similarity; high similarity.

The scores of the 3 tests were standardized in order to make them comparable, and submitted to a trivariate analysis of covariance. Concomitant variables were age and educational level. Type 1 error was experiment-wise checked (Miller, 1967). The means of the 5 experimental groups were found to be significantly different (F = 2.568; d.£.= 12, 333; p < .01). The multiple comparisons

Recognition of random shapes

495

between groups and subtests were carried out according to the method described by Roy and Bose (1953). The 8L subtest turned out to be significantly more difficult than the 4L subtest (F = 42.456; d.£. = 5, 128; p < .0001), and the same was true for 4H compared to 4L (F = 98.766; d.f. = 5, 128; p < .0001). The L+ group performed significantly poorer than controls on the 8L (p < .05) and 4L (p < .05) subtest but not on the 4H subtest. In order to test whether the 5 experimental groups were differentially sensitive to increased number of alternatives and to interitem similarity, the difference between the scores of the 4L and 8L scores, and the difference between the scores of the 4L and 4H conditions were computed. In neither case was the difference between the groups significant. These data lend support to the findings of Bisiach and Faglioni (1974) showing poorer performances of the L + patients on random shapes recognition tasks. However neither the similarity between target and distractors, nor the number of alternatives the subject has to explore appear to be critical in determining these patients' performance.

ExPERIMENT

II

Materials and Method Subjects

Two-hundred-eighteen right-handed subjects were examined. Forty of them were normal controls (C) and 178 were patients with unilateral brain lesions: the left hemisphere group included 103 patients; 82 without (L-) and 21 with VFD (L+ ), the right hemisphere group included 75 patients, 48 without (R-} and 27 with VFD (R+ ). Criteria for the exclusion of a patient were the same as in Experiment I. Stimuli

The stimuli for this experiment were the 16 shapes used in the previous one. Each shape had to be recognized in the corresponding multiple choice display. There were two multiple choice displays: each consisted of 8 vertically arranged items, the first one comprised the starred patterns of the left half of Figure 1, the other one the starred patterns of the right half of the figure. Procedure

The subject was seated in front of the screen of a tachistoscope at a distance of about 50 em. Instructions and a preliminary task were given as in Experiment I. The stimulus was back-projected on the screen of the tachistoscope where its size was nearly the same as that of the printed stimuli. Immediately after the stimulus presentation, the subject was requested to select it from among the alternatives of the multiple choice display. Each stimulus was presented to the subject twice, once with an exposure time of 2.00 sec. and once with an exposure time of 0.50 sec. Therefore the subject had to perform 32 recognitions. The maximum possible error

E. Bisiach, P. Nichelli mid C. Sala

496

score for each of the two conditions was 16. The order of presentation and the stimulus duration were varied according to a fixed random schedule. An error was scored either for a mismatch or when a time of 30 sec. had elapsed without any response.

Results

The mean number of errors (adjusted for age and educational level) of the 5 experimental groups on the two conditions of exposure duration is given in Table II. TABLE II

Mean Recognition Errors (Adiusted for Age and Years of Schooling) of the 5 Experimental Groups at the Two Exposure Conditions

2.00 sec. 0.50 sec.

c

L-

L+

1.5

3.6 4.5

5.0

2.2

3.7

5.3

2.5

4.9

1.8

R-

R+

Statistical analysis was performed according to the criteria described in Experiment I. Type 1 error was again experiment-wise checked. The means of the 5 experimental groups were found to be significantly different (F = 5.334; d.f. = 8, 420; p < .0001). Recognition after 0.50 sec. was found to be significantly more difficult than after 2.00 exposure-time (F = 4.741; d.f. = 5, 211; p < .001). TABLE III

Multiple Comparisons on Error Scores (Adiusted for Age and Educational Level) (* = p < .05}

c L-

L+

R-

2.00 sec 0.50 sec 0.5-2

L-

L+

R-

R+

* *

* *

n.s. n.s. n.s.

n.s.

n.s.

n.s.

2.00 sec 0.50 sec 0.5-2

n.s. n.s. n.s.

2.00 sec 0.50 sec 0.5-2

n.s.

*

n.s.

*

n.s. n.s. n.s. n.s.

* *

n.s. n.s. n.s.

2.00 sec 0.50 sec 0.5-2

n.s.

n.s.

* n.s.

Recognition of random shapes

497

The difference between the scores obtained with 2.00 and 0.50 sec. exposure was calculated in order to test whether the exposure time differentially affected the subjects' performance. Multiple comparisons (Table III) showed that the two left brain-damages groups were significantly different from C and R- patients on both exposure conditions. However, on recognition of briefly exposed (0.50 sec.) stimuli, R + patients also were significantly inferior to C and R- patients. No comparison was significant when the difference between the two exposure conditions was considered as an independent variable.

DISCUSSION

The findings of both experiments substantiate Bisiach and Faglioni's ( 197 4) claim that random shapes recognition is predominantly affected by left brain damage. In every test condition the L + group exhibits the worst performance and, even though the difference between C and L + scores does not reach statistical significance on the 4H subtest of Experiment I, the trend is the same as for the other experimental conditions. Recognition of random shapes seems thus more demanding for the left hemisphere; on the other hand it must be noted that when the same stimuli have been employed in a task of visuo-perceptual categorization (Bisiach, Capitani and Spinnler, 1975) right• brain-damaged patients with visual field defect showed the worst performance. The main difference between these two studies may be that our study, in contrast to that of Bisiach et al. ( 1975 ), required recognition from memory. As Bisiach and Faglioni (1974) have shown, delay is a significant factor in determining the failure of left braindamaged patients on recognition of low association value random shapes. In the second experiment, reducing exposure time was found to expose impairment among R + patients as well, possibly due to limited processing of the array of individual features characterizing the visual stimulus. This would result in a condition similar to the reduction of normal perceptual cues, which according to Milner ( 196 7) would be responsible for the right brain-damaged patients' impaired processing of irregular patterns. It may be speculated that the same severe constraint on the earlier stages of visual processing accounts for the left field advantage reported in most of the studies carried out in normal subjects using lateral tachistoscopic presentation of random shapes (Fontenot, 1973; Dee and Fontenot, 1973; Hellige and Cox, 1976; Endo, Shimizu and Hori, 1978). Our results therefore suggest caution in evaluating lateral field differences on tachistoscopic tasks: reducing exposure time might require special right

498

E. Bisiach, P. Nichelli and C. Sala

hemisphere skills without necessarily implying an overall right hemisphere superiority in dealing with these kinds of patterns. For this reason, analysis of data from clinical populations still represents a valuable - and in many respects unique - source of information for studying hemispheric asymmetry of function. SUMMARY

The performance of unilateral brain-damaged patients on recognition of random shapes was investigated by means of two different experiments. In experiment I interitem similarity and number of response-choice alternatives were varied to evaluate their possible influence on the subjects' performance. In experiment II stimulus exposure time was varied. In both experiments left brain-damaged patients with visual field defect obtained lower scores than control subjects. Right braindamaged patients with visual field defect obtained scores significantly lower than controls only in the brief exposure condition. Acknowledgements. The authors wish to thank dr. Scott D. Lindgren for his revision of the English text. The assistance of the « Centro di Calcolo dell'Universita di Modena» is gratefully acknowledged.

REFERENCES

BISIACH, E., CAPITAN!, E., and SPINNLER, H. (1975) Focal hemisphere damage and visuoperceptual categorization, ]. Neurol. Neurosurg. Psychiat., 38, 1115-1120. - , and FAGLIONI, P. (1974) Recognition of random shapes by patients with unilateral lesions as a function of complexity, association value and delay, Cortex, 10, 101-110. DEE, H. L., and FoNTENOT, D. ]. (1973) Cerebral dominance and lateral differences in perception and memory, Neuropsychologia, 11, 167-173. DE RENZI, E., ScoTTI, G., and SPINNLER, H. (1969) Perceptual and associative disorders of visual recognition. Relationship to the side of the cerebral lesion, Neurology, 19, 634-642. - , and SPINNLER, H. (1966) Visual recognition in patients with unilateral cerebral disease, J. Nerv. Ment. Dis., 142, 515-525. ENDO, M., SHIMIZU, A., and HoRI, T. (1978) Functional asymmetries of visual fields for Japanese word in "kana" (syllable-based) writing and random shapes-recognition in Japanese subiects, Neuropsychologia, 16, 291-297. FoNTENOT, D. ]. (1973) Visual field differences in the recognition of verbal and non verbal stimuli in man, ]. Comp. Physiol. Psycho!., 85, 564-569. HANNAY, H. ]., RoGERS, ]. P., and DURANT, R. F. (1976) Complexity as a determinant of visual field effects for random forms, Acta Psychologica, 40, 29-34. HATTA, T. (1976) Hemisphere asymmetries in the perception and memory of random forms, Psychologia, 19, 157-162. HELLIGE, J. B., and Cox, P. ]. (1976) Effects of concurrent verbal memory on recognition of stimuli from left and right visual fileds, J. Exp. Psycho!.: Human Perc. and Perf., 2, 210-221. HINES, D. (1978) Visual information processing in the left and right hemispheres, Neuropsychologia, 16, 593-599. KIMURA, D. (1963) Right temporal lobe damage, Arch. Neurol., 8, 264-271. MEIER, M. ]., and FRENCH, L. A. (1965) Lateralized deficits in complex visual discrimination and bilateral transfer of reminiscence following unilateral temporal lobectomy, Neuropsychologia, 3, 261-272. MILLER, R. G. (1967) Simultaneous Statistical Inference, McGraw-Hill, New York.

Recognition of random shapes

499

MILNER, B. (1967) Brain mechanisms suggested by studies of temporal lobes, in Brain Mechanisms Underlying Speech and Language, ed. by C. H. Millikan and F. L. Darley, Grune and Stratton, New York. RoY, S. N., and BosE, R. C. (1953) Simultaneous confidence interval estimation, Ann. Math. Stat., 24, 513-536. TYLER, H. R. (1969) Defective stimulus exploration in aphasic patients, Neurology, 19, 105-112. VANDERPLAS, ]. M., and GARVIN, E. A. (1959) The association value of random shapes, ]. Exp. Psycho!., 57, 147-154. Edoardo Bisiach, Centro di Neuropsico!ogia del!'Universita di Milano, Via F. Sforza 35, 20122 Milano, Ita!ia. Paolo Nichelli, Clinica Neurologica, Via del Pozzo 71, Modena, Italia.

Recognition of random shapes in unilateral brain damaged patients: a reappraisal.

RECOGNITION OF RANDOM SHAPES IN UNILATERAL BRAIN DAMAGED PATIENTS: A REAPPRAISAL 1 Edoardo Bisiach, Paolo Nichelli and Claudio Sala (Centro di Neurops...
622KB Sizes 0 Downloads 0 Views