tactual laterality effects and the processing of spatial characteristics: dichaptic exploration of...

TACTUAL LATERALITY EFFECTS AND THE PROCESSING OF SPATIAL CHARACTERISTICS:

DICHAPTIC EXPLORATION OF FORMS BY FIRST AND SECOND GRADE CHILDREN

Jean-Pierre Walch and Jeanine Blanc-Garin

(Laboratoire de Neuropsychologie Humaine, u.A. Cognition et Mouvement E.H.E.S.S. Vieille Charite, Marseille)

INTRODUCTION

Tactual laterality effects (T.L.E.) have recently begun to be considered in neuropsychology. First observed in persons reading Braille, this phenomenon has also been documented using the dichaptic procedure (Witelson, 1974): a bimanual tactual analogy of the previously used dichotic procedure. These dichotomous techniques involve the measurement and comparison of responses to simultaneous stimulations of the right and left perceptual fields. Because sensory projections have privileged access to the contralateral hemisphere, differential responding is generally assumed to reflect, at least in part, differential hemispheric functioning. Thus, a laterality effect (L.E.) in favor of the left hand is generally attributed to the superiority of the right hemisphere at dealing with the given task.

Although a left hand advantage (L.h.A.) was originally found both in persons reading Braille (Hermelin and O'Connor, 1971) and in persons dichaptically exploring nonsense shapes (Wite1son, 1974), non-converging results have been obtained in both cases (see Millar, 1984, for a critical review on Braille; and Gibson and Bryden, 1983, for a review of the results of dichaptic studies). Although L.h.A. was shown to exist in various experiments, some researchers obtained no significant T.L.E., whether in young children (see for example Cranney and Ashton, 1980; Verjat, 1985) or in adults, where even right hand advantages (R.h.A.) were sometimes observed (see for example Labreche, Manning, Gobble and Markman, 1977; Hannay and Smith, 1979). These discrepancies may be due to various factors. First, the task may not be sensitive enough. Also, differences in brain maturation as well as inter-individual differences in processing strategies may playa role. Thus, several factors other than purely structural "hemisphericity", which is debatable (see Beaumont, Young and McManus, 1984, for a critical review on hemisphericity), may be

Cortex (1987) 23, 189-205

190 Jean-Pierre Walch and Jeanine Blanc-Garin

involved. These factors can be viewed as being the result of complex interactions between a given subject and a given task, i.e. how a given subject deals with a given task and how a given procedure influences the way the subject deals with that task (see for example Bryden, 1978; Birkett, 1978; Webster and Thurber, 1978; Bertelson, 1982). A dichaptic task may provide available data on such interactive functioning, provided it is sensitive and reliable enough. Consequently, attempts are currently being made to take the above factors into account (see Dawson, 1981; Cranney and Ahston, 1982; Gibson and Bryden, 1983). Yet, scoring in most studies is based on a dichotomy between correct and incorrect. Such (1) strictly dichotomous and (2) strongly experimenter-dependent scoring may alter the sensitivity of the indexes by causing a loss of information. This loss might in part be responsible for the inconsistencies observed in the results.

In the present study, two refinements have been made on the standard task in order to reduce this loss of information. In response to (1), we propose a finer evaluation of performance by the use of recognition displays which include different types of transformations of the stimuli explored, thus making graduated scoring possible. For (2), we propose basing the scoring on the errors made by the subjects, i.e., relating the scoring method to the way the subject actually performs the task rather than to the way the experimenter thinks the subject will perform it.

We attempted to determine the influence of the above procedure on the T.L.E. obtained, on which side they affect, and on the reliability of the results.

EXPERIMENT I

Materials and Method

Subjects

Testing was done on first-grade children (between 6:3 and 6:6 years old) in the first three months of elementary school (when learning to read). Two groups of children (G 1 and G2) were tested under the same conditions, G2 one year after G 1. G 1 consisted of 11 children (5 boys and 6 girls) and G2 of 13 children (7 boys and 6 girls), making 24 subjects in all (12 boys and 12 girls). All the subjects were right-handed, and did not have problems in school.

Stimuli

Two types of forms were used for haptic exploration. The four letters p, d, b and q (letter task or L.T.), and 4 letter-like forms (shape task or S.T.). The letter-like forms were taken from Gibson, Gibson, Pick and Osper's 1962 study.

Tactual laterality and space in children 191

Fig. 1 - The stimuli of Experiment 1. Upper part: haptically explored stimuli for the two tasks. Lower part: visual recognition, an example of each type of transformation applied to stimuli.

Letters p d b q Shapes ltd 1>19 t:d

.. Associated Stirn. "

Haptic Exploration

Visual .. Recognition

p ,() "0 d bq ppp IO~II

~ ~E;;:PI ld\1J1 ItlLdIZl It) 0 0 :> :> .,. Q) ~ w W N (") I-' 5 Ir Ir

0 o 0 a.: ....i I-' 0 0 0 -I -I -I -I 0 0 Ir a:: Ir ::) Ir

TO T1 T2 T3

These 3.5 X 3.5-cm tactile stimuli were cut out of a 2-mm thick piece of cardboard and glued on cards. The lines that formed the stimuli were 5 millimeters wide.

For visual recognition (see Figure 1), four types of transformations (Tl to T4) were added to each non-transformed stimulus (TO):

Tl: changes in the orientation of the stimulus without alteration of its figural characteristics: 3 rotations in 2-dimensional space: 45°,90° and 180° (ROT.45, ROT.90 and ROT.I80). For the L.T., 2 rotations in 3-dimensional space were added: 1 up-down reversal (UD REV.) and 1 right-left reversal (RL REV.).

T2: 3 transformations of straight line to curve and curve to straight line (LCI and CLI, LC2 and CL2, LC3 and CL3, respectively alterations of one, two, and three parts of the target stimulus.

T3: 3 Transformations in line continuity: 2 opening transformations (OP.) and 1 closure transformation (CL).

T4: maximal transformations: no similarity to the target, the other stimuli and their transformations serving as maximal transformations for a given stimulus (N=28 for the L.T., N.=30 for the S.T.).

Thus, the visual recognition display included forty 3.5 X 3.5-cm drawings (39 transformed stimuli and I target stimulus). Two displays were set up for each task, with a different arrangement of the same 40 drawings for each.


Procedure

The experiment consisted of 2 tasks (L.T. andS.I.) each made up of 8 trials for each subject (4 stimuli X 2 hands). All stimuli were said simply to be forms and no verbalization was required. The stimuli, hidden from view by a screen, were presented in random order, each hand exploring each stimulus once. Each stimulus was paired with another stimulus whose orientation varied across trials. Subjects were not required to recognize visually this associated stimulus (see Figure I), and it was not included in the visual recognition display. Subjects were instructed to "explore both forms, one with each hand" by actively touching them with their index finger. The stimuli were presented lying flat and were fastened to the horizontal board in order to allow proper exploration. There was no imposed time limit for exploration and subjects usually took about 15 seconds per trial. A slight tap on one of the child's hands indicated which stimulus was to be recognized. A 25 X 4O-cm visual recognition display (8 rows X 5 columns) was immediately presented, lying flat on the table. Subjects were told that they were to give one answer only and "that the exact drawing could be anywhere on the visual display". They were thus instructed to scan the whole display on their own before giving an answer. Before the test, a training session was conducted (with other stimuli and a smaller recognition display) in order to accustom the child to the procedure and to establish proper exploration. Each subject completed the two tasks in two sessions occurring at at least a week's interval. Half of the subjects of each sex began with the L.T., the other half with the S.T.

Results

Performance

Overall results (i.e. of both tasks, both hands, and both groups taken together) show that the children understood the task well, choosing the picture of the target stimulus, TO, 44.01% of the, time, and the TI, T2 and T3 transformations 33.86% of the time. The T4 transformations were chosen less often (22.13%), although their probability of occurrence in the visual recognition displays was high (72.5%).

Further analyses were made by correcting the frequency with which a given type of transformed stimulus was chosen according to its probability of occurrence in the visual recognition displays. The response patterns of the two tasks were similar, despite differences in performance level. Data are given in Figure 2.

We can distinguish five levels in the frequencies at which the pictures proposed in the displays were chosen, corresponding to the way the children actually performed the tasks. The 5 levels were classified from A to E, goins from best to worst. Maximal transformations (T4) may be considered as "rejected", i.e. chosen significantly less often than by chance (E choices: t= 19.02, p<.OOO5). Four of the other transformed

Tactual laterality and space in children

Fig. 2 - Results of Experiment / (data for both hands, both tasks, and both groups are taken together). Upper part: frequencies at which each type of transformed stimuli was chosen (chance corrected), in ascending order. Lower part: the five choice levels (E to A) determined from response frequencies and used for weighting scores (from 0 to J 0, see text for details).

+40

+30

+ 20

+10

CHANCE

-10

TRANSF.

TYPES

CHOICE LEVEL WEIGHT. SCORE

% '±' CHANCE

* P';; .10

** P< .05

*** p< .005 **** p< . 0005 Student 's t test

********** .

*"';;*

g I-' N C') ..,. 0 n: 0 0

t- CI: 0 ..J ..J

E 0

0 4

r-rnT

'" ~ 0 (jj ..,. 'f!.

I-' f- ~ CI: 0 .,j 0 !f~~ ..J CI: 0 :::J CI:

C B

5 6 I 6 .5

193

**** r--

0 t-

A

10

stimuli seemed to provide relevant features for differentiation and were rejected, although less so: ROT.90, OP., LC2, and LC3 (D choices: t between 2.7 and 7.3, P < .02). Two of the transformed stimuli were chosen at chance level: ROT.45 and CL. (Cchoices: t= .98 and t=.05 respectively, NS). Four of the transformed stimuli were "accepted", i.e. chosen significantly more often than by chance: UD REV., ROT. 180, Lei and RL.REV. (B choices: t between 1.4 and 4.4, p. between ;10 and .(01). Finally, the target stimulus (TO) was chosen most often, i.e. highly accepted (A choices: t= 18.62, p<.OO(5).

In order to obtain an index that would fully represent the information conveyed by the errors made, and thus correspond to the finest possible evaluation of performance, we used the result pattern shown in Figure 2 to

Gl+G2

TABLE I

Performance: MMn WI. Scores (Experiment /)

M F

M+F

L.T. S.T, 57,45 59.22 58.34

40,02 45.28 42.65


weight each type of response: scores ranged from 0 (E choices) to 10 (A choices). According to this weighted index (W.I.), a subject's overall performance for a given task could fall between 0 (8 E choices) and 80 (8 A choices). Averages are given in Table I for each task and each sex.

A three-way analysis of variance was conducted on the W.1. scores, using the factors sex, hand, and task. The analysis showed that the L.T. was significantly easier than the S.T. (F= 18.74; d.f.= 1, 22; p<.OOI). Moreover, the tendancy of girls to be better than boys existed but was insignificant (F=.93; d.f.= 1,22). Finally, there was no significant sexby-task interaction (F=.53; d.f.=I, 22).

Tactual Laterality Effects (TL.E.)

The frequency at which each type of transformed stimuli was chosen was plotted for each hand, each task, and each group in Figure 3.

The response patterns was consistent. Furthermore, this pattern was obtained for both tasks, with both Gland G2. As compared to the right hand, when using the left hand the low-level choices (E and D) and the intermediate-level choices (C) were made less often and the high-level choices (A and B) were made more often. Nevertheless, the response patterns were similar for both hands. This pattern was more distinct for the S.T. than for the L.T.

In an attempt to determine the value of weighting responses, two different indexes were used to score the T.L.E.: a strictly dichotomous index (D.I.) and a weighted index (W.I.). Using both indexes, the difference between the performance of the two hands was calculated for each subject at each task (see Table II). With the conservative, dichotomous criterion (number of A choices, individual performance between 0 and +4 for each hand), none of the T.L.E. turned out to be significant. However, significant differences were obtained using the other index (W.I.: individual performance between 0 and +40 for each hand).

The analysis of variance that was applied to the W.I. scores revealed that the factor "hand" was a significant source of variation (F = 6; d.f. = 1, 22; p<.025) and that there was a marginally significant sex-by-handby-task interaction (F=2.93; d.f.= 1,22; p=.lO).

For the population taken as a whole, no significant L.h.A. existed for the L.T. but did exist for the S.T. Girls showed an L.h.A. in the L.T. (p<.02 by Wilcoxon's test) and boys in the S.T. (p<.015 by Wilcoxon's test). This result was true for both Gland G2 (see Table II).

Individual Differences

The responses were also examined by classifying each subject according to the existence of an L.h.A. or of an R.h.A. (based on the W.I.) for


% ! CHANCE LEVEL

+50 ..

G1 G2

+30

.: ." I~ . ili~ """" ",n ____ ~ .. !..-___ _

I" .l :;. ./ . -20

. E D c B A E D c B A

G1 ;/ . :" G2

·30

+to

-----~+---CHANCE LEVEL--~~-----

. / .. :/ . . / •

-20

195

L.T .

.......... RIGHT HAND

.--. L EFT HAND

S. T .

Fig. 3 -- Results of Experiment 1. Performance of each hand, for each task (L T.: upper part, and S. T.: lower part), and each group (Gl: left part, and G2: right part). On each graph, response frequency (chance corrected) for each choice level (E to A).


TABLE II

T.L.E. Obtained with the Dichotomous Index (D.I.: left part) and with the Weighted Index (W 1.: right part), for the L. T. and the S. T. (Experiment I). An L.h.A. is indicated by a Positive

Value

D.1. W.1.

L.T. S.T. L.T. S.T.

M (5) + 0.60 + 1.00 M (5) + 3.68 + 6.20* Gl F (6) + 0.33 - 0.50 F (6) + 6.52* + 0.60

M+F (11) + 0.45 + 0.09 M+F (11) + 5.10 + 3.40*

M (7) - 0.28 + 0.28 M (7) - 2.50 + 4.64* G2 F (6) + 0.33 0.00 F (6) + 4.43* + 2.00

M+F (l3) 0.00 + 0.l5 M+F (l3) + 0.93 + 3.31 * M (12) + 0.09 + 0.50 M (12) + 0.55 + 5.14**

Gl+G2 F (12) + 0.34 - 0.25 F (12) + 5.38** + 1.30 M+F (24) + 0.21 + 0.13 M+F (24) + 2.96 + 3.23**

* p.< 10; ** p<.05 by Wilcoxon's Matched-Paired Signed-Rank Test.

each task. Raw data are presented in Table III. In the L.T., the difference between the number of children showing a

T.L.E. in favor of one side or the other only bordered significance. Girls showed a significant effect in favor of the left hand, whereas boys showed no significant effect.

In the S.T., results indicated that significantly more children performed better with their left hand than with their right hand. Boys showed a significant effect, whereas girls did not.

In summary, the sensitivity of our dichaptic task was improved by the use of a weighted index for scoring responses. The performance level was significantly higher when performing the L.T. than the S.T. Taken as a whole, children showed a significant L.h.A. when performing the S.T. and an insignificant L.h.A. during the L.T. Girls showed a significant L.h.A. on the L.T., whereas boys showed a significant L.h.A. on the S.T. This pattern occurred for both groups with averaged data, and was confirmed by considering individual hand-advantage scores.

TABLE III

Distribution of Subjects by Hand Advantage with the WI. (Experiment I)

L.T. S.T.

L.h.A. Equal. R.h.A. p* L.h.A. Equal. R.h.A. p*

M (12) 6 0 6 10 0 2 .019 F (12) 9 1 2 .033 8 0 4

M+F (24) 15 1 8 .105 18 0 6 .011

* Binomial test.


Discussion

Our aim was to analyze the capability of children to extract spatial relationships when learning to read and not to compare a "verbal" task and a "spatial" task. Thus, the material used for the two tasks was presented to the subjects as forms and the subjects were not required to verbalize. This point differs from Witelson's (1974) and other studies in which the verbal nature of the material was emphasized. The performance on the L.T. was significantly better than on the S.T. One might think that the material proposed for the L.T. was less complex than that proposed for the S.T. Furthermore, although the children were just beginning to learn to read, it is possible that some of them were more familiar with letter stimuli.

Regarding T.L.E., the sex-by-hand-by-task interaction shown to exist was unexpected. The significant L.h.A. demonstrated by boys only, when performing the S. T., is consistent with a number of studies using a dichaptic procedure (see Witelson, 1976; Cioffi and Kandel, 1979; Dawson, 1981; Gibson and Bryden, 1983; Gibson and Bryden, 1984, for age 10). On the contrary, the significant L.h.A. demonstrated by girls only, when performing the L.T., is rather surprising and puzzling. One interpretation of these results would be that there exists a differential reaction between sexes to the increasing spatial complexity of the material,ail L.h.A. been implemented at a low level of spatial complexity by girls (i.e. in the L.T.) and at a high level by boys (i.e. in the S.T.). But, since we cannot assume that the two tasks differed only by this variable, such an interpretation is debatable. In the L.T., task demand might have been affected by inter-subject differences in familiarity with letters. In any case, processing strategies are to be taken into account and interpretations in terms of sex-related structural differences in brain organization are not supported because of the variability observed in the data collected (see Mc Glone, 1980, and commentaries).

Nevertheless, three ideas clearly emerge from this first experiment. First, the "errors" made by the children contain information about the way they process spatial relationships. It may be noted that the transformed stimuli most often considered by the children as equivalent to the target stimulus were those that changed the orientation of the target stimulus in two- or three-dimensional space but did not change its form (UD REV., ROT. 180, RL REV.). However, among this type of transformation, two of the rotations (ROT.90 and ROT.45) are less often chosen: as noted for example by Braine (1978), "uprightness" is an important component of ·form for young children. Yet, when the transformations strongly altered some intrafigural characteristic of the target stimulus (OP., LC2, LC3), cues were sufficient for stimulus rejection. Second, the


use of scoring methods that attempt to take the way subjects perform a task into account (i.e. one of the subject-dependent variables) makes the test more sensitive than standard procedures. Third, T.L.E. were clearly shown to exist on tasks easily accepted by children, made up of sessions brief enough to avoid losing their interest. The similarity of the patterns obtained for the two groups shows that the findings are reliable from the inter-individual standpoint.

In order to test the intra-individual reliability of the results, we conducted a second experiment with another group of subjects, in which the same children performed the S.T. twice.

EXPERIMENT II

Materials and Method

Basically the same general method was used, with only some minor changes.

Subjects

Testing was done on 12 right-handed, normal children, 6 boys and 6 girls. The same subjects were tested twice at a year's interval, under the same conditions. One of the boys that had participated in the first test had moved away before the second test, so he was replaced by another boy (of the same age in the same classroom). At the completion of the first test, children were in the last three months of first grade (between 6:9 and 7 years old).

Stimuli

Haptic exploration. There were six letter-like forms to be tactually explored (see Figure 4). The task was thus made up of 12 trials for each subject (6 stimuli X 2 hands). The 3.5 X 3.5-cm haptic stimuli were made of imitation wood and glued on wooden cards, and the lines that formed the stimuli were 5 millimeters wide. A different associated stimulus was paired with each of the six stimuli for a given subject in order to avoid overfamiliarity with the same associated stimulus after several trials. Each associated stimulus was paired an equal number of times with each target stimulus throughout the experiment, all subjects taken together. The stimuli were fastened vertically at a convenient distance, based on the length of the subject's index fingers. Subjects were blindfolded and their wrists were attached to the horizontal board. The time limit for exploring was 13 seconds.

Visual recognition. Immediately after haptic exploration, a 32 X 24-cm visual recognition display was presented in the upright position. It contained 20 drawings (4 rows of 5 drawings). The number of drawings was decreased in this experiment (as compared to Experiment I) so as to encourage the subjects to scan the display thoroughly before responding. Two displays were set up for each


SHAPES k1 1\ L ASSOCIA. STI M. 11 [b ~

.-Haptic

Visual •

Ld ~J7I LO 0 ~

ex> ,.... I-' I-' 0 0 a:: a::

TO T1

Q( + Ir I:h n ~

E .xploration

Recognition

bJ ~ U > w a:: ...J a::

cL o

T3

Li CJ)

o

199

Fig. 4 - The stimuli of Experiment II. Upper part: haptically explored stimuli. Lower part: visual recognition, an example of each type of transformation applied to stimuli.

target stimulus (the same 20 drawings arranged differently). The 12 displays were constructed in such a way that the arrangement of each type of picture was counterbalanced. They did not include the drawings of the associated stimuli ~hich were not to be visually recognized. Each display contained 20 drawmgs: - 13 maximal transformations, - 3 transformations bearing on intrafigural relationships: 1 opening (OP), 1 in which a detail was removed and the global shape was maintained (GS), I in which the global shape was altered and a detail was retained (DS), - 3 position changes without changing form: I RL REV., I ROT.45, 1 ROT.I80, - I with no transformation: the target stimulus.

Results

Performance

Data for each test was processed in the same way as in the first experiment. In both PI and P2, maximal and DS transformations were "rejected", ROT.45 and RL REV. transformations were chosen at chance level, and GS transformations and the target stimulus were highly "accepted". Performance on PI and P2 was only slightly different: ROT.180 transformations were no longer "accepted" on P2 (see Figure 5).

200 Jean-Pierre Walch and Jeanine .Blanc-Garin

TAANSF.

TYPES

% ± CHANCE 0 P1 m P2

P<·10 •• p < '05 Student 's I test

P < ·005 •••• P <·Q005

It) 'f I-'

'f a: en a? I- 0 0

CHOICE L.I01) E D

WEIGHT. SC.I.') 0 4

::> 0 UJ S! a: '=' ...J a? a:

C B

5 6

en 0 C!l I-

A

7.5 10

Fig. 5 -Results of Experiment II. Upperpart:forthe two tests (PI and P2), frequencies at which each type of transformed stimuli was chosen (chance corrected), in ascending order of choices made during Pl. Lower part: the five choice levels (E to A) determined from PI response frequencies and used for weighting scores (from 0 to 10).

Five response levels appeared evident by the pattern of PI andwere used to set up a weighted index for scoring responses, as in the first experiment. A three-way analysis of variance was performed on the W.I. scores, using the factors sex, hand and test. The analysis showed that the factor sex and the factor test were not significant sources of variation (F=.73, d.f.= 1,10, and F=.36, d.f.= 1,10 respectively). Furthermore, there was no significant sex-by-test interaction (F= 1.50, d.f.= 1, 10)

Tactual Laterality Effects (T.L.E.)

The frequency at which each type of transformed stimuli was chosen was plotted for each hand and each test in Figure 6. The response pattern was oonsistent for both PI and P2. As compared to the right hand,when using the left hand the low- and intermediate- level choices (E, D and C) were made less often and the high-level choices (Aand B) were made more often.

Scoring with the D.I. (number of correct responses), a significant L.h.A. was shown to exist on PI for all children taken together. Girls


Fig. 6 - Results of Experiment II. Performance of each hand for each test (PI and P2). On each graph, response frequencies . (chance corrected) for each choice level (E to A).

+30

+10

% ± CHANCE L ... . . ....

....... RIGHT HAND

.-. LEFT " "

!I CHANCE I------:,..:....,~-- / .. ~ ....

•.. -10

ii' iii iii' EOCBA EOCBA

P1 P2

201

exhibited a significant L.h.A., whereas boys exhibited an insignificant one. On P2, none of the T.L.E. turned out to be significant (see Table IV). Using the W.I., a significant L.h.A. was shown to exist for all children taken together both on PI and on P2. On PI, girls again exhibited a significant L.h.A., whereas boys again showed an insignificant one (see Table IV). The three-way analysis of variance applied to the W.1. scores revealed that the factor hand was the only significant source of variation (F=5.23; d.f.= 1,10; p<.045).

TABLE IV

T.L.E. Obtained with the Dichotomous Index (D'/.), and with the Weighted Index (W/') for the Two Tests: PI and P2 (Experiment II). An L.h.A. is indicated by a Positive Value

PI P2

D.1. W.1. D.1. W.I.

M (6) + 1.00 + 3.83 + 0.33 + 8.00 F (6) + 0.66* + 6.83* + 0.16 + 4.67

M+F (12) + 0.83* + 5.34** + 0,09 + 6.33*

* p<.lO; ** p<.05 Wilcoxon's Matched-Paired Signed-Rank Test.

Individual Data

The number of subjects of each sex showing (or not) an L.h.A. was nearly the same on PI and P2. Nevertheless, among the 11 children available for this comparison, only 7 (3 boys and 4 girls) exhibited a


consistent hand advantage between PI and P2 (p = .324 by the binomial test). Two children (one of each sex) exhibited a shift from an R.h.A. to an L.h.A. and two (again one of each sex) exhibited a shift from an L.h.A. to an R.h.A .. This latter shift was accompanied by an important decrease in overall performance. The correlation between overall performance and the strengh of the L.h.A. was positive but insignificant (R= .36).

Discussion

Better spatial processing was expected on P2, one year later than PI, so the lack of improvement is surprising. The only improvement made was that 1800 rotation was no longer accepted on P2 (see Figure 5). This lack of improvement is not due to an alteration in the performance of the two hands since differences between the left and right hand remain similar. However, some data from another experiment currently in progress have shown that for unimanual exploration, response patterns are similar to those of dichaptic exploration, and performance improves. Thus, we must distinguish optimal capabilities (competence) and the ability to deal with the conflict of the dichaptic condition. Further data including more subjects and a wider range of ages are necessary in order to extend such investigations.

The use of a weighted index for scoring responses (based on the subject's errors) again makes the test more sensitive than standard procedures. Furthemore, the results are more reliable (see Table IV). The present findings are clearly in agreement with those obtained in the first experiment.

The significant L.h.A. shown to exist in right-handed children (ages 7 and 8) appears consistently, at least as a group effect. Indeed, individual L.h.A. across time was not as reliable. If this task is a valid indicator of lateral differences, then such results might reflect a modification in perceptuo-cognitive strategies or an alteration of the hemispheric balance for some children.

The significant sex differences obtained in Experiment I did not reoccur in Experiment II. As noted by Bradshaw (1980) sex differences are often weak and superimposed upon pre-existing effects. Furthemore, laterality effects can be influenced by the variability in processing strategies (see Bryden, 1978, 1980; Blanc-Garin and Andrau-Wendling, 1984). Thus, regarding sex differences, we must be cautious in interpreting the results of a simple experiment in which the use of a particular processing strategy and the level of functional asymmetry cannot be dissociated. Longitudinal studies are needed to investigate this important question.


GENERAL DISCUSSION

Dichaptic exploration of forms, followed by visual recognition, may be used successfully to evaluate both spatial processing ability and lateral differences.

Spatial processing levels in these two experiments can hardly be compared since stimuli are slightly different. However, orientation transformations (without form change) are used in both experiments. As can be seen in Table V, these transformations were progressively less often chosen with increasing age. This result exists for all data collected for the S.T., i.e. through a comparison of the results of children of three age groups: 6:3 to 6:6 years old (Experiment 1),6:9 to 7 years old and 7:9 to 8 years old (Experiment II). These data are in agreement with data collected by developmental psychologists suggesting that form progressively becomes dependent on orientation in children (see Piaget and Inhelder, 1947; Gibson et al., 1962). However, probably due to conflictual conditions, spatial performance in dichaptic tasks does not reflect the optimal competence of children: unimanual tasks would be preferable to this end.

TABLE V

Frequencies of Choice, 'above ( + ) or below ( - ) Chance Levels, of Orientation Transformations with Increasing Age for the S. T. (Experiment I and Experiment II)

Age

6:3 to 6:6 6:9 to 7

, 7:9 to 8

RLREV

(--) + 1.19 - 0.79

ROT.45

+ 0.60 - 1.45 - 0.13

* p<.l0 by Student's tat test; (- -) no data available.

ROT. 180

+ 4.66 * + 2.50 * + 0.53

Experiment I Experiment II Experiment II

As for lateral differences, the significant left hand advantage shown to exist in right-handed children when exploring shapes argues in favor of the view that performance at our task is dictated, at least in part, by the differing capacities of the two hemispheres. This idea is supported by the consistent occurrence of this pattern in two independent groups (see Experiment I) as well as in the same group at a year's interval (see Experiment II).

Nevertheless, the regular occurrence of individual differences shown to exist in the first experiment (see Table III), as well as the limited test-retest correlation observed in the second experiment, show that the underlying phenomenon, even if consistent at the group level, is more complex and more flexible at the individual level. As stressed by Bryden (1978), this underlying phenomenon may result from the way in which an individual's control system and brain organization interact. This type of

204 lean-Pierre Walch and leanine Blanc-Garin

interaction certainly enables (may be even favors) the expression of the individual differences stated above. Whether or not sex is in itself a factor related to this interaction is not clear from our data. If sex differences exist, they can be weak and masked by other individual factors. In other words, in experiments bearing on a small number of subjects, the factor sex can overlap other individual variables.

The present experiments have shown that basing the scoring on the subject's errors improves the sensitivity of the dichaptic task as well as the reliability of the group results. Furthermore, it illustrates that the responses given by the subject provide some information about the way children process spatial relationships. This finer analysis of their performance also permits truly qualitative comparisons (see Table V). Our technique would be particularly useful for comparing normal and pathological populations (slow learners of reading, for example) according to spatial processing level and lateral differences. It would thus be possible to see if performance (i.e. level of processing) and the expression of T.L.E. (i.e. hemispheric balance) are really linked. Individual as well as developmental analyses would be particularly well adapted to such investigations.

ABSTRACT

Tactual laterality effects (T.L.E.) were examined in first- and second-grade children when performing a dichaptic task. Our procedure, a modified version of Witelson's standard dichaptic task, emphasized the type of errors made, so that we could construct a weighted index (W.I.) for scoring rather than a strictly dichotomous one. The same data were compared using the two types of scoring indexes stated above. T.L.E. occurred consistently with the W.I. scores only, both in two independent groups or in the same group at a year's interval, suggesting (1) that a strictly dichotomous index might lead to loss of information, (2) that the results are reliable at least at the group level. Results are discussed in terms of possible applications of such a procedure to investigating the relationship between performance (spatial processing) and brain organization (hemispheric balance).

REFERENCES

BEAUMONT, J.G., YOUNG, A.W., and McMANUS, I.e. Hemisphericity: a critical review. Cognitive Neuropsychology, 1: 191-212, 1984.

BERTELSON, P. Lateral differences in normal man and lateralization of brain function. International Journal of Psychology, 17: 173-210, 1982.

BIRKETT, P. Hemisphere differences in the recognition of nonsense shapes: cerebral dominance or strategy effects? Cortex, 14: 245-249, 1978.


BLANC-GARIN, J., and ANDRAU-WENDLING, B. Les variables individuelles en Neuropsychologie: a propos de l'asymetrie hemispherique. Psychologie Franr;aise, 29: 81-84, 1984.

BRADSHAW, J.L. Sex and side:-a double dichotomy interacts. The Behavioral and Brain Sciences, 3: 229-230, 1980.

BRAINE, L.G. A new slant on orientation perception. American Psychologist, 33: 10-22, 1978.

BRYDEN, M.P. Four strategy effects in the assessment of hemispheric asymmetry. In G . Underwood (Ed.), Strategies of Information Processing. London: Academic Press, 1978.

BRYDEN, M.P. Sex differences in brain organization: different brain or different strategies? The Behavioral and Brain Sciences, 3: 230-231 , 1980.

CIOFFI, J. , and KANDEL, G .L. Laterality of stereognostic accuracy of children for words, shapes, and bigrams: a sex difference for bigrams. Science, 204: 1432-1434, 1979.

CRANNEY, J., and ASHTON, R. Witelson's dichaptic task as a measure of hemispheric asymmetry in deaf and hearing populations. Neuropsychologia, 18: 95-98, 1980.

CRANNEY, J., and AHSTON, R. Tactile spatial ability: lateralized performance of deaf and hearing age groups. Journal of Experimental Child Psychology, 34: 123-134, 1982.

DAWSON, G.D. Sex differences in dichaptic processing. Perceptual and Motor Skills, 53: 935-944, 1981.

GIBSON, c., and BRYDEN, M.P. Dichaptic recognition of shapes and letters in children. Canadian Journal of Psychology, 37: 132-143, 1983.

GIBSON, c., and BRYDEN, M.P. Cerebral laterality in deaf and hearing children. Brain and Language, 23: 1-12, 1984.

GIBSON, E.J., GIBSON, J.J., PICK, A.D., and aSPER, H. A developmental study of the discrimination of letter-like forms. Journal of Comparative and Physiological Psychology, 6: 897-906, 1962.

HANNAY, H.J., and SMITH, A.C. Dichaptic perception of forms by normal adults. Perceptual and Motor Skills, 49: 991-1000, 1979.

HERMELIN, B., and O'CONNOR, N. Functional asymmetry in the reading of Braille. Neuropsychologia, 2: 431-435, 1971.

LABRECHE, T.M., MANNING, A.A., GOBLE, W., and MARKMAN, R. Hemispheric specialization for linguistic and nonlinguistic tactual perception in a congenitally deaf population. Cortex, 13: 184-194, 1977.

MCGLONE, J. Sex differences in human brain asymmetry: a critical survey. The Behavioral and Brain Sciences, 3: 215-263, 1980.

MILLAR, S. Is there a "best hand" for Braille? Cortex, 20: 75-87, 1984. PIAGET, J., and INHELDER, B. La Representation de l'Espace chez l'Enfant. Paris: Presses

Universitaires de France, 1947. VERJAT, I. Fragilite de I'expression de l'asymhrie fonctionnelle cerebrale a travers la modalite

tactilo-kinesthesique chez l'enfant. Unpublished Doctoral Dissertation, University of Grenoble, France, 1985.

WEBSTER, W.G., and THURBER, A.D. Problem-solving strategies and manifest brain asymmetry. Cortex, 14: 474-484, 1978.

WITELSON, S.P. Hemispheric specialization for linguistic and nonlinguistic tactual perception using a dichotomous stimulation technique. Cortex, 10: 3-17, 1974.

WITELSON, S.P. Sex and the single hemisphere: specialization of the right hemisphere for spatial processing. Science, 193: 425-427, 1976.

Jean-Pierre Walch, Jeanine Blanc-Garin, Laboratoire de Neuropsychologie Humaine, V .A. 11661a Vieille Charite, 2, Rue de la Charite, 13002 Marseille, France.

tactual laterality effects and the processing of spatial characteristics: dichaptic exploration of...

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