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Directionality in Right, Mixed and Left Handers
DIRECTIONALITY IN RIGHT, MIXED AND LEFT HANDERS George B. Karev (Section of Anthropology, IEMA, Bulgarian Academy of Sciences)
ABSTRACT Directionality in right, mixed and left handers was studied, asking subjects to draw 6 familiar objects. All three handedness classes showed left directional bias, but they differed significantly in this respect, right handers being the most and left handers the least left directed. Directionality is related to handedness, but it seems to be governed by an autonomous underlying mechanism, which probably developed in the course of evolution to facilitate the perceptuo-motor relationships of the subject with the environment. Key words: handedness, directionality, laterality, drawing
INTRODUCTION More than 110 years ago, Wilson wrote: “An unpremeditated profiledrawing, if done by a right-handed draftsman, will be represented looking to the left; as, if it is the work of left-handed draftsman, it will certainly look to the right” (Wilson, 1885, cited by Alter, 1989). Numerous studies of cerebral organization link the right hemisphere to higher visuospatial processing capabilities (Bryden, 1982). For instance, right hemisphere superiority in face recognition has been reported (see Rhodes, 1985a, for a review). A substantial number of cases of prosopagnosia with lesions apparently confined to the right hemisphere have been described (De Renzi, 1986), although it is possible that prosopagnosia resulting from a right hemisphere lesion may concurrently involve some atypical condition of the left hemisphere (Benton, 1990). Subjects prefer symmetrical composite faces, constructed by duplicating the half-face that appears on their left (see Rhodes, Ronke and Tan, 1990, for a review). Damage in the right hemisphere eliminates the left bias (Kolb, Milner and Taylor, 1983) and left handers are not initially biased towards the left (Gilbert and Bakan, 1973; Rhodes, 1985b). Another left perceptual bias has been found in recognition of facial emotional expressions (De Renzi, Faglioni and Spinnler, 1968; Hansh and Pirozzolo, 1980; Manning, 1986; Lane, Kivley, Dubois et al., 1995). Here, considerable handedness effects have also been reported (Heller and Levy, 1981; Levy, Heller, Banich et al., 1983; David, 1989). “Aesthetic” preference, another result of cognitive and emotional processing, is also influenced by asymmetrical organization of the brain. Levi (1976) found the “aesthetic” preferences of right handers on complex pictures to be associated with the asymmetry of their content, pictures with centre of interest displaced to the right being preferred to those with the centre of interest displaced to the left. At the same Cortex, (1999) 35, 423-431
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George B. Karev
time, the orientation preference of left handers was uninfluenced by the asymmetry of the picture content. It was proposed that judging the “aesthetic” value of a picture differentially activates the right hemisphere, thus producing an attentional bias toward the left. Pictures with their centre of interest displaced to the right compensate for this attentional imbalance and are therefore preferred by right handers. Freimuth and Wapner (1979) found that pictures with implied motion from left-to-right are preferred to those with implied motion from right-to-left. In contrast, Banich, Heller and Levy (1989) reported convincing data that slides with right-biased content and right-to-left motion are favoured by right handers, while slides preferred by left handers have neither asymmetry of content, nor asymmetry of motion. Alter (1989) proposed a visuomotor task, the drawing of several familiar objects, as a means of assessing directionality. The six objects, proposed by Alter and used in the present study, are quite different in their nature. Two of them are living creatures, three are transport vehicles and one, the jug, is the most static object among the six. Since the jug has a handle, a direct handedness effect could be suspected in its directionality – right handers being unconsciously inclined to draw the jug with its handle directed towards their right hand and the opposite for the left handers. The aim of the present study is two-fold. First, to apply Alter’s method to right, mixed and left handers. Second, to examine whether the nature of the drawn object is relevant to its contribution to directionality. MATERIALS
AND
METHODS
Subjects Students, ranging in age from 15 to 19 years, from randomly selected secondary schools, were orally questioned as to which hand they used to write, draw, throw, cut with scissors, hammer a nail into wood and work with a screwdriver. Those who answered that they preferred the left hand in any one of these activities were tested on the questionnaire of Chapman and Chapman (1987). From the students who used the right hand in all the activities considered in the verbal interview, 264 presumed right handers were randomly selected and tested on the same questionnaire. Thus, 754 subjects participated in this study: 270 left handers (144 males, 126 females), 220 mixed handers (123 males, 97 females) and 264 right handers (132 males, 132 females). Assessment of Handedness On each of the 13 activities of Chapman and Chapman’s (1987) questionnaire, subjects were asked to answer whether they performed it with their right hand (scored “1”), with either hand (scored “2”) or with their left hand (scored “3”). Thus, subjects’s scores varied from 13 to 39. In accordance with the original procedure, those with scores of 13 to 17 were designated as right handers (RH), from 18 to 32 as mixed handers (MH) and from 33 to 39 as left handers (LH). In addition, subjects with handedness scores of 13 were designated as consistent right handers (CRH) and those with handedness scores of 39 as consistent left handers (CLH). Assessment of Directionality Each subject was asked to draw sketches of 6 familiar objects: a bicycle, a dog walking, a bus, a facial profile, an airplane and a jug (Alter, 1989). Three changes were made to Alter’s procedure. First, to avoid any discomfort in
Directionality and handedness
425
Fig. 1 – Example of the drawings of a CRD subject.
drawing, the use of the “dominant’ or “nondominant” hand was not required; all subjects were allowed to use the hand they preferred. Second, some of the students in the pilot study tried to look at the sketches of their neighbours or to ask for help in drawing. In the present study, subjects were seated far enough from each other to prevent unwanted association. Third, in the pilot study a considerable number of the sketches of the bus showed front and rear parts so similar that it was impossibile to define direction. In the present study, the bus was replaced with a lorry which eliminated this problem. Directionality index, D, was scored as (R – L)/(R + L), or the number of right orientated objects minus the number of left orientated ones, divided by the sum of all drawn objects. Thus, subjects’ scores ranged from – 1 (consistently left-directed, CLD) to + 1 (consistently right-directed, CRD). By way of illustration, the sketches of one of the CRD-subjects are shown in Figure 1. All the subjects with positive D were designated as right-directed (RD), those with D = 0 were designated as mixed-directed (MD) and those with negative D were considered left-directed (LD).
RESULTS In order to see whether consistency of handedness is of any importance for directionality, CLH (N = 38) were contrasted to the nonconsistent LH (N = 232). The difference between the mean D-scores was far from being statistically significant (t = .36, n.s.). In a similar way, CRH (N = 90) were compared to the nonconsistent RH (N = 174). Again, the difference between mean D-scores was found to be very far from being statistically significant (t = .58, n.s.). Significant interaction was found between handedness and directionality (F = 32.97, d.f. = 2, 751, p < .005). The mean values of D, by handedness group and sex, are presented in Table I. All nine means (two for each sex and the total in the three handedness classes) are negatively signed, i.e. right-to-left orientated sketches prevail in all the hand preference groups and in the gender subgroups.
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George B. Karev TABLE I
Mean Values of D in the Three Handedness Groups Directionality: mean values of D Handedness
Sex Males Females Total Males Females Total Males Females Total
RH MH LH
N
Mean
SD
132 132 264 123 97 220 144 126 270
– 0.740 – 0.791 – 0.765 – 0.477 – 0.437 – 0.460 – 0.317 – 0.349 – 0.332
0.525 0.442 0.485 0.663 0.659 0.660 0.744 0.707 0.726
The sex differences within RH, MH and LH are small and far from being statistically significant (t = .85, t = .44 and t = .36, respectively). Concerning the total means, RH are significantly exceeded by the LH (t = 8.17, d.f. = 533, p < .001) and by the MH (t = 7.09, d.f. = 483, p < .05). The percent distributions of the three directionality groups within each handedness category are presented in Table II. The numerical values from the “Total” rows of this table were chi2-tested as a 3 × 3 contingency table. The results showed that, in general, RH, MH and LH differ significantly in their directionality and that LD-, MD- and RD-subjects differ significantly in their handedness (x2c = 32.73, d.f. = 4, p < .001, with Yates correction). When the particular differences were further tested, it turned out that left-directed subjects among RH exceeded significantly those among MH (u = 4.20, p < .001) and among LH (u = 5.69, p < .001); the difference between proportions of LD among MH and among LH was not significant (u = 1.31, n.s.). Proportion of right-directed subjects among RH was significantly lower that that among MH (u = 3.52, p < .001) and among LH (u = 5.38, p < .001), and the difference between MH and LH failed to reach significance (u = 1.72, n.s.). TABLE II
Percent Distributions of the Three Directionality Groups within Each Handedness Category Directionality LD
MD
RD
Total
Handedness
Sex
N
%
N
%
N
%
N
%
RH
Males Females Total Males Females Total Males Females Total
115 115 230 90 68 158 95 84 179
87.12 87.12 87.12 73.17 70.10 71.82 65.97 66.67 66.30
1 7 8 8 7 15 6 9 15
0.76 5.30 3.03 6.50 7.22 6.82 4.17 7.14 5.56
16 10 26 25 22 47 43 33 76
12.12 7.58 9.85 20.33 22.68 21.36 29.86 26.19 28.15
132 132 264 123 97 220 144 126 270
100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.01
MH LH
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427
80
70
60
RH MH
%
50
LH
40
30
20
10
0 – 1.00
– 0.67
– 0.33
0
0.33
0.67
1.00
D score
Fig. 2 – Percent distributions of the three handedness classes on the D-values.
Distributions of D-scores in the three handedness classes are shown in Figure 2. The percent frequencies of the three handedness groups for D = – 1 rank RH, MH and LH in descending order, which is reversed for D = 1. The most impressive difference between the distribution curves is the pronounced excess of the RH at D = – 1, and the steepest descending part of their distribution curve. On the other hand, all three curves are similar and L-shaped. Table III presents the absolute numbers and per cent frequencies of the rightdirected sketches in each handedness class for each object separately. When numerical values were chi2-tested as 6 × 3 contingency table, no significant
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George B. Karev TABLE III
Absolute Numbers and Percent Frequencies of the Right-directed Sketches of the Six Objects in the Three Handedness Groups. (The columns “p < ...” contain the significance levels of the differences between corresponding frequencies) Handedness RH (N = 264) Object Jug Bicycle Lorry Airplane Walking dog Human face Total
MH (N = 220)
LH (N = 270)
N
%
p < ...
N
%
p < ...
N
%
19 44 31 41 31 20 186
7.20 16.67 11.74 15.53 11.74 7.58 11.74
0.001 0.01 0.001 0.001 0.001 0.001 0.001
56 63 56 71 64 47 357
25.45 28.64 25.45 32.27 29.09 21.36 27.05
0.05 n.s. n.s. n.s. n.s. 0.05 0.001
92 97 84 92 96 79 541
34.07 35.93 31.11 34.07 35.56 29.26 33.40
relation between object and handedness was found (x2c = 9.608, d.f. = 10, n.s.). This result was expected, since it is evident from the table that a common trend is observed in all six objects: the frequency of right-directed drawings increases from RH, through MH, to LH. This trend is very well expressed; among all the differences between the per cent frequencies in neighbouring columns of the table, only four failed to reach statistical significance. To evaluate whether the nature of the drawn object affected its directionality, the objects were compared to each other for their lack of correspondence with the subjects’ D-scores. In the MD-subjects (N = 38), D-score of 0 appeared in 3 right- and 3 left-oriented sketches. Therefore, only 716 subjects, those with a signed D, were included in this comparison (LD, N = 567, and RD, N = 149). First, the 373 cases of discrepancy with the subject’s D were recorded by directionality of the subject and by object, as shown in Table IV. The data presented showed a highly significant directionality by object interaction (x2c = 43.19, d.f. = 5, p < .001, with Yates correction). Second, particular comparisons were made between the objects in their total percentages of discrepancy, presented in the last row of the table. The two objects with the highest rates, the jug and the human face, did not differ significantly from each other in these rates (u = 1.83, n.s.), but each of them exceeded significantly the other four objects (e.g., human face vs. airplane, u = 2.67, p < .01. Third, when RH and LH were compared in their incidences of jugTABLE IV
Incidence of Orientational Discrepancies of the Particular Objects with the Subjects’ Directionalities Objects Subjects LD RD Total
N %
Total
Jug
Bicycle
Lorry
Airplane
Dog
Face
54 56 110 29.49
39 10 49 13.14
20 8 28 7.51
47 12 59 15.82
31 8 39 10.46
34 54 88 23.59
225 148 373 100.01
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429
discrepancies (5 in left-directed and 17 in right-directed right handers vs. 33 in left-directed and 23 in right-directed left handers), the resulting 2 × 2 table showed a highly significant excess (x2c = 6.90, d.f. = 1, p < .01) of these discrepancies in right-directed over left-directed RH and in left-directed over right-directed LH. That means that dextrals, even right-directed, draw the jug directed to the left, i.e. with the handle towards their right hand; just the same trend, in the opposite direction, is observed in the left handers. DISCUSSION Our results revealed that consistency of handedness is of no importance to the mean D-scores of the handedness groups. Therefore, in studies like the present, the wider criteria for handedness (e.g., Chapman and Chapman, 1987) are more convenient than those defining consistent left and right handers only (e.g., Alter, 1989). All three handedness classes differ significantly from each other in their directionality. This is unequivocal evidence of a connection between the two lateralities. On the other hand, all the means were negative, i.e., the drawings of all three handedness categories were directed leftwards, though to a different degree. This contrasts the two lateralities with each other and testifies to their autonomy much more emphatically than Alter’s (1989) results. The mirror symmetry between the D-scores distribution curves of the three handedness groups, described by Alter (1989), was not observed at all. On the contrary, the three distribution curves were L-shaped and similar to each other, this being an indirect argument in favour of an unique and autonomous mechanism, underlying directionality. The general impression from the reported results is that directionality is a kind of cerebrally determined laterality, related to handedness, but governed by a separate and distinct underlying mechanism. Our findings can be interpreted as the final result of two tendencies, in conflict and at the same time complementary to one another. Significant interaction between handedness and directionality, along with significant differences between the three handedness categories in their particular D-means unequivocally show the mutual connection between the two lateralities. However, the gradual change of D from RH to LH, the negative score of all D-means, as well as the similarity in the shapes of Ddistributions in the three handedness groups, testify in favour of an unique and autonomous mechanism, underlying directionality. The second aim of the present study arose from the different nature of the objects used. On the one hand, all objects followed the trend to be more rightdirected in MH than in RH and in LH than in MH. On the other hand, among the 716 subjects with a signed D, the jug was most frequently drawn facing the opposite way with the sign of D, followed by the human face. The rates of discrepancy of these two objects with subjects’ directionality exceeded significantly those showed by the remaining four. It has been stated that the ability to recognize faces is “special” and in some sense unique (Hay and Young, 1982). Levine, Banich and Koch-Weser (1988)
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reviewed several arguments that face recognition is qualitatively different from other pattern recognition abilitities. To the neuropsychological peculiarities of the human face in recognition tasks our study adds a different peculiarity – directional specificity in drawing the human face. As for the jug, it is the most static object among the six and, as mentioned above, it is the only with a handle. Our results showed that it ranked first in its lack of coincidence with the subjects’ directionality. The rate of this discrepancy exceeded significantly those of other objects except the human face. The most intriguing finding here is that even right-directed dextrals tend to draw the jug with its handle towards their right hand; correspondingly, even left-directed left-handers prefer to draw the jug with its handle towards their left hand. In other words, it turned out that, unlike the other 5 objects, in the drawing of the jug a particular mechanism is undeniably in action. It is an unconscious trend of both right and left handers to draw the jug with the handle directed towards their dominant hands; this phenomenon could be named a direct handedness effect. Our results concerning directionality are consistent, at least indirectly, with the finding that pictures representing right-to-left motion of the objects are “aesthetically” preferred by RH and that LH do not show such an asymmetry (Banich et al., 1989). It is hardly possible to speculate which is primary: whether the subject “aesthetically” prefers the object moving in a given direction because he/she would draw it directed in the same way, or he/she draws it directed leftor rightwards because his/her “aesthetic” judgement favours this direction of movement. What is more, while the activities in “aesthetic” judgement are mainly perceptual and evaluative, those governing directionality in drawing are predominantly motor and creative. This point deserves further investigation. In conclusion, the simplest explanation of our results is to ascribe the findings concerning directionality to right hemisphere activation in drawing and to corresponding left attentional bias. Right-handedness is characteristic of all human cultures, and it is a biological rather than a cultural endowment (Corballis, 1983, 1989, 1997). It is tempting to hypothesize that directionality developed as a distinct kind of laterality, related to handeness so as to facilitate the perceptuo-motor relationships of the subject with the environment. Thus, it serves right handedness best of all. When mixed and especially left handedness come in conflict with this function, they considerably reduce the phenotypic expression of directionality, but even left handedness is not able to reverse directionality towards the right. Acknowledgements. The author thanks the school-heads and teachers for their cooperation in the field work and all the students who volunteered for this study. I am grateful to “Pharmatzia-Dupnitza AD” and especially to the National Science Fund of the Ministry of Education, Sciences and Technologies for the financial support and to Mr. Allan Kachelmeier for linguistic assistance. The author is most grateful to the Editor and two anonymous referees for their constructive criticisms on earlier versions of the manuscript. REFERENCES ALTER, I. A cerebral origin for “directionality”. Neuropsychologia, 27: 563-573, 1989. BANICH, M.T., HELLER, W., and LEVY, J. Aesthetic preference and picture asymmetries. Cortex, 25: 187195; 1989. BENTON, A. Facial recognition 1990. Cortex, 26: 491-499, 1990.
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BRYDEN, M.P. Laterality: Functional Asymmetry in the Intact Brain. New York: Academic Press, 1982. CHAPMAN, L.J., and CHAPMAN, J.P. The measurement of handedness. Brain and Cognition, 6: 175-183, 1987. CORBALLIS, M.C. Human Laterality. New York: Academic Press, 1983. CORBALLIS, M.C. Laterality and human evolution. Psychological Review, 96: 492-505, 1989. CORBALLIS, M.C. The genetics and evolution of handedness. Psychological Review, 104: 714-727, 1997. DAVID, A. Perceptual asymmetry for happy-sad chimeric faces: Effects of mood. Neuropsychologia, 11: 355-362, 1989. DE RENZI, E. Current issues of prosopagnosia. In H.D. Ellis, M.A. Jeeves, F. Newcombe and A. Young (Eds.), Aspects of Face Processing. Dordrecht: Martinus Nijhoff, 1986. DE RENZI, E., FAGLIONI, P., and SPINNLER, H. The performance of patients with unilateral brain damage on face recognition tasks. Cortex, 4: 17-34, 1968. GILBERT, C., and BAKAN, P. Visual asymmetry in perception of faces. Neuropsychologia, 11: 355-362, 1973. FREIMUTH, M., and WAPNER, S. The influence of lateral organization in the evaluation of paintings. British Journal of Psychology, 70: 211-218, 1979. HANSH, E.C., and PIROZZOLO, F. Task relevant effects on the assessment of cerebral specialization for facial emotion. Brain and Language, 10: 51-59, 1980. HAY, D.C., and YOUNG, A.W. The human face. In A.W. Ellis (Ed.), Normality and Pathology in Cognitive Functions. London: Academic Press, 1982. HELLER, W., and LEVY, J. Perception and expression in right-handers and left-handers. Neuropsychologia, 19: 263-272, 1981. KOLB, B., MILNER, B., and TAYLOR, L. Perception of faces by patients with localized cortical excisions. Canadian Journal of Psychology, 37: 8-18, 1983. LANE, R.D., KIVLEY, L.S., DUBOIS, M.A., SHAMASUNDARA, P., and SCHWARTZ, G.E. Levels of emotional awareness and the degree of right hemisphere dominance in the perception of facial emotion. Neuropsychologia, 33: 525-538, 1995. LEVINE, S.C., BANICH, M.T., and KOCH-WESER, M.P. Face recognition: A general or specific righthemisphere capacity? Brain and Cognition, 8: 303-325, 1988. LEVY, J. Lateral dominance and aesthetic preference. Neuropsychologia, 14: 431-445, 1976. LEVY, J., HELLER, W., BANICH, M.T., and BURTON, L.A. Asymmetry of perception in free vision of chimeric faces. Brain and Cognition, 2: 404-419, 1983. MANNING, L. Interhemispheric asymmetry in facial expression recognition: Relationship to fielddependence. Cortex, 22: 601-610, 1986. RHODES, G. Lateralized processes in face recognition. British Journal of Psychology, 76: 249-271, 1985a. RHODES, G. Perceptual asymmetries in face recognition. Brain and Cognition, 4: 197-218, 1985b. RHODES, G., RONKE, K., and TAN, S. Asymmetries in face perception: Component process, face specificity and expertize effects. Cortex, 26: 13-32, 1990. WILSON, D. Paleolitic dexterity. Transactions of the Royal Society of Canada, 2: 119-133, 1885. George B. Karev, M.D., Ambassadeur, Ambassade de Bulgarie, 4 Avenue de Mecnés, Rabat, B.P. 1301, Maroc.
(Received 13 March 1998; accepted 11 November 1998)
ABSTRACT Directionality in right, mixed and left handers was studied, asking subjects to draw 6 familiar objects. All three handedness classes showed left directional bias, but they differed significantly in this respect, right handers being the most and left handers the least left directed. Directionality is related to handedness, but it seems to be governed by an autonomous underlying mechanism, which probably developed in the course of evolution to facilitate the perceptuo-motor relationships of the subject with the environment. Key words: handedness, directionality, laterality, drawing
INTRODUCTION More than 110 years ago, Wilson wrote: “An unpremeditated profiledrawing, if done by a right-handed draftsman, will be represented looking to the left; as, if it is the work of left-handed draftsman, it will certainly look to the right” (Wilson, 1885, cited by Alter, 1989). Numerous studies of cerebral organization link the right hemisphere to higher visuospatial processing capabilities (Bryden, 1982). For instance, right hemisphere superiority in face recognition has been reported (see Rhodes, 1985a, for a review). A substantial number of cases of prosopagnosia with lesions apparently confined to the right hemisphere have been described (De Renzi, 1986), although it is possible that prosopagnosia resulting from a right hemisphere lesion may concurrently involve some atypical condition of the left hemisphere (Benton, 1990). Subjects prefer symmetrical composite faces, constructed by duplicating the half-face that appears on their left (see Rhodes, Ronke and Tan, 1990, for a review). Damage in the right hemisphere eliminates the left bias (Kolb, Milner and Taylor, 1983) and left handers are not initially biased towards the left (Gilbert and Bakan, 1973; Rhodes, 1985b). Another left perceptual bias has been found in recognition of facial emotional expressions (De Renzi, Faglioni and Spinnler, 1968; Hansh and Pirozzolo, 1980; Manning, 1986; Lane, Kivley, Dubois et al., 1995). Here, considerable handedness effects have also been reported (Heller and Levy, 1981; Levy, Heller, Banich et al., 1983; David, 1989). “Aesthetic” preference, another result of cognitive and emotional processing, is also influenced by asymmetrical organization of the brain. Levi (1976) found the “aesthetic” preferences of right handers on complex pictures to be associated with the asymmetry of their content, pictures with centre of interest displaced to the right being preferred to those with the centre of interest displaced to the left. At the same Cortex, (1999) 35, 423-431
424
George B. Karev
time, the orientation preference of left handers was uninfluenced by the asymmetry of the picture content. It was proposed that judging the “aesthetic” value of a picture differentially activates the right hemisphere, thus producing an attentional bias toward the left. Pictures with their centre of interest displaced to the right compensate for this attentional imbalance and are therefore preferred by right handers. Freimuth and Wapner (1979) found that pictures with implied motion from left-to-right are preferred to those with implied motion from right-to-left. In contrast, Banich, Heller and Levy (1989) reported convincing data that slides with right-biased content and right-to-left motion are favoured by right handers, while slides preferred by left handers have neither asymmetry of content, nor asymmetry of motion. Alter (1989) proposed a visuomotor task, the drawing of several familiar objects, as a means of assessing directionality. The six objects, proposed by Alter and used in the present study, are quite different in their nature. Two of them are living creatures, three are transport vehicles and one, the jug, is the most static object among the six. Since the jug has a handle, a direct handedness effect could be suspected in its directionality – right handers being unconsciously inclined to draw the jug with its handle directed towards their right hand and the opposite for the left handers. The aim of the present study is two-fold. First, to apply Alter’s method to right, mixed and left handers. Second, to examine whether the nature of the drawn object is relevant to its contribution to directionality. MATERIALS
AND
METHODS
Subjects Students, ranging in age from 15 to 19 years, from randomly selected secondary schools, were orally questioned as to which hand they used to write, draw, throw, cut with scissors, hammer a nail into wood and work with a screwdriver. Those who answered that they preferred the left hand in any one of these activities were tested on the questionnaire of Chapman and Chapman (1987). From the students who used the right hand in all the activities considered in the verbal interview, 264 presumed right handers were randomly selected and tested on the same questionnaire. Thus, 754 subjects participated in this study: 270 left handers (144 males, 126 females), 220 mixed handers (123 males, 97 females) and 264 right handers (132 males, 132 females). Assessment of Handedness On each of the 13 activities of Chapman and Chapman’s (1987) questionnaire, subjects were asked to answer whether they performed it with their right hand (scored “1”), with either hand (scored “2”) or with their left hand (scored “3”). Thus, subjects’s scores varied from 13 to 39. In accordance with the original procedure, those with scores of 13 to 17 were designated as right handers (RH), from 18 to 32 as mixed handers (MH) and from 33 to 39 as left handers (LH). In addition, subjects with handedness scores of 13 were designated as consistent right handers (CRH) and those with handedness scores of 39 as consistent left handers (CLH). Assessment of Directionality Each subject was asked to draw sketches of 6 familiar objects: a bicycle, a dog walking, a bus, a facial profile, an airplane and a jug (Alter, 1989). Three changes were made to Alter’s procedure. First, to avoid any discomfort in
Directionality and handedness
425
Fig. 1 – Example of the drawings of a CRD subject.
drawing, the use of the “dominant’ or “nondominant” hand was not required; all subjects were allowed to use the hand they preferred. Second, some of the students in the pilot study tried to look at the sketches of their neighbours or to ask for help in drawing. In the present study, subjects were seated far enough from each other to prevent unwanted association. Third, in the pilot study a considerable number of the sketches of the bus showed front and rear parts so similar that it was impossibile to define direction. In the present study, the bus was replaced with a lorry which eliminated this problem. Directionality index, D, was scored as (R – L)/(R + L), or the number of right orientated objects minus the number of left orientated ones, divided by the sum of all drawn objects. Thus, subjects’ scores ranged from – 1 (consistently left-directed, CLD) to + 1 (consistently right-directed, CRD). By way of illustration, the sketches of one of the CRD-subjects are shown in Figure 1. All the subjects with positive D were designated as right-directed (RD), those with D = 0 were designated as mixed-directed (MD) and those with negative D were considered left-directed (LD).
RESULTS In order to see whether consistency of handedness is of any importance for directionality, CLH (N = 38) were contrasted to the nonconsistent LH (N = 232). The difference between the mean D-scores was far from being statistically significant (t = .36, n.s.). In a similar way, CRH (N = 90) were compared to the nonconsistent RH (N = 174). Again, the difference between mean D-scores was found to be very far from being statistically significant (t = .58, n.s.). Significant interaction was found between handedness and directionality (F = 32.97, d.f. = 2, 751, p < .005). The mean values of D, by handedness group and sex, are presented in Table I. All nine means (two for each sex and the total in the three handedness classes) are negatively signed, i.e. right-to-left orientated sketches prevail in all the hand preference groups and in the gender subgroups.
426
George B. Karev TABLE I
Mean Values of D in the Three Handedness Groups Directionality: mean values of D Handedness
Sex Males Females Total Males Females Total Males Females Total
RH MH LH
N
Mean
SD
132 132 264 123 97 220 144 126 270
– 0.740 – 0.791 – 0.765 – 0.477 – 0.437 – 0.460 – 0.317 – 0.349 – 0.332
0.525 0.442 0.485 0.663 0.659 0.660 0.744 0.707 0.726
The sex differences within RH, MH and LH are small and far from being statistically significant (t = .85, t = .44 and t = .36, respectively). Concerning the total means, RH are significantly exceeded by the LH (t = 8.17, d.f. = 533, p < .001) and by the MH (t = 7.09, d.f. = 483, p < .05). The percent distributions of the three directionality groups within each handedness category are presented in Table II. The numerical values from the “Total” rows of this table were chi2-tested as a 3 × 3 contingency table. The results showed that, in general, RH, MH and LH differ significantly in their directionality and that LD-, MD- and RD-subjects differ significantly in their handedness (x2c = 32.73, d.f. = 4, p < .001, with Yates correction). When the particular differences were further tested, it turned out that left-directed subjects among RH exceeded significantly those among MH (u = 4.20, p < .001) and among LH (u = 5.69, p < .001); the difference between proportions of LD among MH and among LH was not significant (u = 1.31, n.s.). Proportion of right-directed subjects among RH was significantly lower that that among MH (u = 3.52, p < .001) and among LH (u = 5.38, p < .001), and the difference between MH and LH failed to reach significance (u = 1.72, n.s.). TABLE II
Percent Distributions of the Three Directionality Groups within Each Handedness Category Directionality LD
MD
RD
Total
Handedness
Sex
N
%
N
%
N
%
N
%
RH
Males Females Total Males Females Total Males Females Total
115 115 230 90 68 158 95 84 179
87.12 87.12 87.12 73.17 70.10 71.82 65.97 66.67 66.30
1 7 8 8 7 15 6 9 15
0.76 5.30 3.03 6.50 7.22 6.82 4.17 7.14 5.56
16 10 26 25 22 47 43 33 76
12.12 7.58 9.85 20.33 22.68 21.36 29.86 26.19 28.15
132 132 264 123 97 220 144 126 270
100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.01
MH LH
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427
80
70
60
RH MH
%
50
LH
40
30
20
10
0 – 1.00
– 0.67
– 0.33
0
0.33
0.67
1.00
D score
Fig. 2 – Percent distributions of the three handedness classes on the D-values.
Distributions of D-scores in the three handedness classes are shown in Figure 2. The percent frequencies of the three handedness groups for D = – 1 rank RH, MH and LH in descending order, which is reversed for D = 1. The most impressive difference between the distribution curves is the pronounced excess of the RH at D = – 1, and the steepest descending part of their distribution curve. On the other hand, all three curves are similar and L-shaped. Table III presents the absolute numbers and per cent frequencies of the rightdirected sketches in each handedness class for each object separately. When numerical values were chi2-tested as 6 × 3 contingency table, no significant
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George B. Karev TABLE III
Absolute Numbers and Percent Frequencies of the Right-directed Sketches of the Six Objects in the Three Handedness Groups. (The columns “p < ...” contain the significance levels of the differences between corresponding frequencies) Handedness RH (N = 264) Object Jug Bicycle Lorry Airplane Walking dog Human face Total
MH (N = 220)
LH (N = 270)
N
%
p < ...
N
%
p < ...
N
%
19 44 31 41 31 20 186
7.20 16.67 11.74 15.53 11.74 7.58 11.74
0.001 0.01 0.001 0.001 0.001 0.001 0.001
56 63 56 71 64 47 357
25.45 28.64 25.45 32.27 29.09 21.36 27.05
0.05 n.s. n.s. n.s. n.s. 0.05 0.001
92 97 84 92 96 79 541
34.07 35.93 31.11 34.07 35.56 29.26 33.40
relation between object and handedness was found (x2c = 9.608, d.f. = 10, n.s.). This result was expected, since it is evident from the table that a common trend is observed in all six objects: the frequency of right-directed drawings increases from RH, through MH, to LH. This trend is very well expressed; among all the differences between the per cent frequencies in neighbouring columns of the table, only four failed to reach statistical significance. To evaluate whether the nature of the drawn object affected its directionality, the objects were compared to each other for their lack of correspondence with the subjects’ D-scores. In the MD-subjects (N = 38), D-score of 0 appeared in 3 right- and 3 left-oriented sketches. Therefore, only 716 subjects, those with a signed D, were included in this comparison (LD, N = 567, and RD, N = 149). First, the 373 cases of discrepancy with the subject’s D were recorded by directionality of the subject and by object, as shown in Table IV. The data presented showed a highly significant directionality by object interaction (x2c = 43.19, d.f. = 5, p < .001, with Yates correction). Second, particular comparisons were made between the objects in their total percentages of discrepancy, presented in the last row of the table. The two objects with the highest rates, the jug and the human face, did not differ significantly from each other in these rates (u = 1.83, n.s.), but each of them exceeded significantly the other four objects (e.g., human face vs. airplane, u = 2.67, p < .01. Third, when RH and LH were compared in their incidences of jugTABLE IV
Incidence of Orientational Discrepancies of the Particular Objects with the Subjects’ Directionalities Objects Subjects LD RD Total
N %
Total
Jug
Bicycle
Lorry
Airplane
Dog
Face
54 56 110 29.49
39 10 49 13.14
20 8 28 7.51
47 12 59 15.82
31 8 39 10.46
34 54 88 23.59
225 148 373 100.01
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discrepancies (5 in left-directed and 17 in right-directed right handers vs. 33 in left-directed and 23 in right-directed left handers), the resulting 2 × 2 table showed a highly significant excess (x2c = 6.90, d.f. = 1, p < .01) of these discrepancies in right-directed over left-directed RH and in left-directed over right-directed LH. That means that dextrals, even right-directed, draw the jug directed to the left, i.e. with the handle towards their right hand; just the same trend, in the opposite direction, is observed in the left handers. DISCUSSION Our results revealed that consistency of handedness is of no importance to the mean D-scores of the handedness groups. Therefore, in studies like the present, the wider criteria for handedness (e.g., Chapman and Chapman, 1987) are more convenient than those defining consistent left and right handers only (e.g., Alter, 1989). All three handedness classes differ significantly from each other in their directionality. This is unequivocal evidence of a connection between the two lateralities. On the other hand, all the means were negative, i.e., the drawings of all three handedness categories were directed leftwards, though to a different degree. This contrasts the two lateralities with each other and testifies to their autonomy much more emphatically than Alter’s (1989) results. The mirror symmetry between the D-scores distribution curves of the three handedness groups, described by Alter (1989), was not observed at all. On the contrary, the three distribution curves were L-shaped and similar to each other, this being an indirect argument in favour of an unique and autonomous mechanism, underlying directionality. The general impression from the reported results is that directionality is a kind of cerebrally determined laterality, related to handedness, but governed by a separate and distinct underlying mechanism. Our findings can be interpreted as the final result of two tendencies, in conflict and at the same time complementary to one another. Significant interaction between handedness and directionality, along with significant differences between the three handedness categories in their particular D-means unequivocally show the mutual connection between the two lateralities. However, the gradual change of D from RH to LH, the negative score of all D-means, as well as the similarity in the shapes of Ddistributions in the three handedness groups, testify in favour of an unique and autonomous mechanism, underlying directionality. The second aim of the present study arose from the different nature of the objects used. On the one hand, all objects followed the trend to be more rightdirected in MH than in RH and in LH than in MH. On the other hand, among the 716 subjects with a signed D, the jug was most frequently drawn facing the opposite way with the sign of D, followed by the human face. The rates of discrepancy of these two objects with subjects’ directionality exceeded significantly those showed by the remaining four. It has been stated that the ability to recognize faces is “special” and in some sense unique (Hay and Young, 1982). Levine, Banich and Koch-Weser (1988)
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reviewed several arguments that face recognition is qualitatively different from other pattern recognition abilitities. To the neuropsychological peculiarities of the human face in recognition tasks our study adds a different peculiarity – directional specificity in drawing the human face. As for the jug, it is the most static object among the six and, as mentioned above, it is the only with a handle. Our results showed that it ranked first in its lack of coincidence with the subjects’ directionality. The rate of this discrepancy exceeded significantly those of other objects except the human face. The most intriguing finding here is that even right-directed dextrals tend to draw the jug with its handle towards their right hand; correspondingly, even left-directed left-handers prefer to draw the jug with its handle towards their left hand. In other words, it turned out that, unlike the other 5 objects, in the drawing of the jug a particular mechanism is undeniably in action. It is an unconscious trend of both right and left handers to draw the jug with the handle directed towards their dominant hands; this phenomenon could be named a direct handedness effect. Our results concerning directionality are consistent, at least indirectly, with the finding that pictures representing right-to-left motion of the objects are “aesthetically” preferred by RH and that LH do not show such an asymmetry (Banich et al., 1989). It is hardly possible to speculate which is primary: whether the subject “aesthetically” prefers the object moving in a given direction because he/she would draw it directed in the same way, or he/she draws it directed leftor rightwards because his/her “aesthetic” judgement favours this direction of movement. What is more, while the activities in “aesthetic” judgement are mainly perceptual and evaluative, those governing directionality in drawing are predominantly motor and creative. This point deserves further investigation. In conclusion, the simplest explanation of our results is to ascribe the findings concerning directionality to right hemisphere activation in drawing and to corresponding left attentional bias. Right-handedness is characteristic of all human cultures, and it is a biological rather than a cultural endowment (Corballis, 1983, 1989, 1997). It is tempting to hypothesize that directionality developed as a distinct kind of laterality, related to handeness so as to facilitate the perceptuo-motor relationships of the subject with the environment. Thus, it serves right handedness best of all. When mixed and especially left handedness come in conflict with this function, they considerably reduce the phenotypic expression of directionality, but even left handedness is not able to reverse directionality towards the right. Acknowledgements. The author thanks the school-heads and teachers for their cooperation in the field work and all the students who volunteered for this study. I am grateful to “Pharmatzia-Dupnitza AD” and especially to the National Science Fund of the Ministry of Education, Sciences and Technologies for the financial support and to Mr. Allan Kachelmeier for linguistic assistance. The author is most grateful to the Editor and two anonymous referees for their constructive criticisms on earlier versions of the manuscript. REFERENCES ALTER, I. A cerebral origin for “directionality”. Neuropsychologia, 27: 563-573, 1989. BANICH, M.T., HELLER, W., and LEVY, J. Aesthetic preference and picture asymmetries. Cortex, 25: 187195; 1989. BENTON, A. Facial recognition 1990. Cortex, 26: 491-499, 1990.
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(Received 13 March 1998; accepted 11 November 1998)