作者：Nimet nay Gündoan    作者单位：土耳其安卡拉，巴斯肯特大学医学院生理系

【摘要】  目的：评估大学生群体优势眼和左/右利手间的关系。方法：受试对象为179名大学生志愿者，平均年龄为19.4±1.6岁，其中女110 名（61.5%），男69 名（38.5%）。优势眼由Gündoan和McManus两种方法测得，左或右利手则由Edinburgh Handedness Inventory Oldfield和McManus法确定，t检验评估实验的可信度。结果：Gündoan法测得受试者中110人（61.5%）为右眼优势，69人（38.5%）为左眼优势，无性别差异。McManus法重测相同受试者，则右/左眼优势分别为128人（71.5%）和51人（28.5%）。两法测得的结果相关，一致度κ=0.256（P<0.01）。女性受试者中，Gündoan法测得右/左眼优势分别为62人（56.4%）和48 人（43.6%），McManus法测得的结果为右/左眼优势分别为74人（67.3%）和36人（32.7%）。Fisher检验两法测得的结果相关（P<0.05），一致度κ=0.239 （P<0.01）。男性受试者中，Gündoan法测得右/左眼优势为48 人（69.6%）和21人（30.3%），McManus法检测为54人（78.3%）和15人（21.7%）。Fisher检验两法测得结果相关（P>0.05），一致度κ=0.239（P<0.01）。Oldfield和McManus法分别测得右利手比例为91.6%（n=164）和91.1% （n=163），两者间有较高的一致度κ=0.753（P<0.01）。McManus法检测出的优势眼和左或右利手间的统计学相关性具有显著性意义（Fisher检测P<0.017；一致度评分phi=0.193（P<0.05）。结论：大学生以右利手为主，McManus法检测发现右利手似乎与有眼优势更为相关。左或右利手和优势眼似乎是研究大脑功能不对称性和大脑偏侧型的最可靠的方法。

【关键词】  左/右利手；优势眼；大脑功能不对称性；大脑偏侧型

　　INTRODUCTION

　　In humans, two cerebral hemispheres appear to be nearly symmetrical; however each hemisphere has some anatomical, chemical and functional specializations. The right cerebral hemisphere is dominant in visiospatial and nonverbal function such as art, architecture, geometry and mathematics, whereas the left cerebral hemisphere is dominant in recent verbal memory, neural control of writing and speaking and producing language. Interestingly, slight differences in using different brain areas for language processing were recognized between males and females [13]. The specialization of cerebral hemispheres in certain functions of human body is believed to cause some subtle changes in the neural chemical and functional aspects of the different organs and systems. Previous studies to date have concluded that in the righthanded population, righteye dominance was greater than the lefteye dominance and just the opposite in the lefthanded population [46]. Moreover it was suggested that the dominant eye had higher intraocular pressure compared to the nondominant one [7]. Preference for the left eye over rather than the right eye for monocular tasks such as sighting through a tube, was the basis for the conclusion that about one third of the population is left eye dominant [8]. Dominant eye is associated with hand preference which is most conventionally assessed in terms of the hand which is used for writing. Many theorists, particularly in the area of education, have focused on cerebral functional asymmetry called laterality which was diagnosed by hand preference. But various times the educational system has strongly encouraged all children to write with their right hand. Obviously manifested handedness may altered by educational training. On the other hand eye dominance is not changed all through the life by educational training or social influences which means detection of eye dominance is more fundamental measure of underlying cerebral laterality[911]. The aim of this study was to evaluate the relationship between eye dominance and handedness in order to clarify inconsistent results in the literature with detection most reliable method for evaluating functional cerebral laterality due to eye dominance or handedness.

　　MATERIALS AND METHODS

　　This study was performed in accordance with the ethical standards of the Declaration of Helsinki 1994 which was approved by the local Ethics Committee of Bakent University (KA06/04). 179 university students aged between 1624 years (mean age, 19.4±1.6 years) were enrolled in the study by giving their informed consent. The majority of the students were female (61.5%). All of the subjects were healthy, without any systemic, chronic or acute illnesses.

　　Determination of Hand Preference

　　Oldfield test  Hand skill was assessed by performance measurement. All subjects were tested individually in the same laboratory room during 12.0013.00 PA with adequate instruments. Handedness was assessed according to the Edinburgh Inventory Oldfield test[12,13] . Findings were evaluated by the Geshwind [14] and Tan [15] scoring system. Subjects having handedness scores smaller than zero were considered lefthanded; those with scores greater than zero were considered to be righthanded. Mixedhandedness was excluded as Bourassa[9].

　　McManus test  Another evaluation of handedness was assessed by performance measurement according to the McManus[16] test, based on the determination of the throwing hand skill. Subjects were asked to throw, a magnetic arrow at a target on a wall 23m away. The subjects made 10 throws. The well skilled hand for throwing was considered as dominant.

　　Determination of the Dominant Eye

　　Gündoan test  The dominant eye performance measurement method was described previously[11] which was adapted from the Rosenbach [17] and the Miles[4].

　　McManus test  Another evaluation of the eyedness was assessed by performance measurement according to the McManus [16] and Porac[18] tests in which there was three items for eye sighting, such as: looking down a microscope, looking into a dark bottle, looking through a keyhole [16,8]. Scores were tallied on a point scale (1=always left, 2=either, 3=always right), with the either responses excluded. The dominant eye was accepted to be the left eye if the average score was< 2 and to be the right eye if total score was ≥2.

　　Statistical Analysis  Data were shown as n (%). χ2 and Fisher exact test were used for the analysis of categorical data. The agreement between different methods was analyzed with Kappa statistics. Comparison of proportions was made by two proportions z test. P<0.05 was considered as significant. Statistical analysis was performed using the SPSS 11.5 and MINITAB 13.0 for Windows.

　　RESULTS

　　Without gender difference right handedness ratios among students were 91.6% (n=164) and 91.1% (n=163) according to the Oldfield and the McManus tests, respectively.

　　Table 1Dominant eye results in female of two methods（略）

　　Table 2Dominant eye results in males of two methods（略）

　　Table 3  Relationship between eye dominance and handedness tests with the respect to revealed frequencies according to the Gündoan and the Oldfield tests（略）

　　Table 4  Relationship between eye dominance and handedness result according to the Gündoan and McManus (throwing hand) tests（略）

　　Table 5  Relationship between eye dominance and handedness results according to the McManus and Oldfield tests（略）

　　The overall incidence of the left handedness determined by the Oldfield [12] test was 8.4 %, which is very close to the ratio of 8.9 % by the McManus[16] test results (Table 1). The statistical agreement between two test results were also represented with a high score (κ=0.753, P<0.01).  Without gender difference right/left eye dominance were found respectively 110 (61.5 %), 69 (38.5%) by Gündoan test. When the same subjects were retested by McManus test method the right/left eye dominance was found respectively 128 (71.5%), 51 (28.5%). The results of these two methods  were related significantly (χ2 =12.378, P<0.01; Fisher exact test P<0.01), with an agreement score κ=0.256, (P<0.01, Figure 1).        

　　Table 6  Comparison of eye dominance and hand preference frequencies obtained via different detection　tests for the same subjectsn（略）

　　Figure 1  Without gender difference dominant eye results for two methods（略）

　　In females the right/left eye dominance were found respectively as 62 (56.4%), 48 (43.6%) by Gündoan test as it was found 74 (67.3%), 36(32.7%) for the same subject when they retest by McManus test According McManus test results 74 subjects were found with right eye dominance and 36 subjects were found with left eye dominance. But only 48 of the 74 subjects were assessed with right eye dominance by the Gündoan test and the rest of 26 were assessed with left eye dominance. In the McManus test 36 subjects were found with left eye dominance, but among those only 22 subjects assessed with left eye dominance according to the Gündoan test. The rest of 14 subjects were assessed with right eye dominance. In the Gündoan test 62 subject were found with right eye dominance, 48 subjects were found with left eye dominance (Table 1). The results of these two tests for females were related significantly by Fisher exact test (P<0.05), with agreement score κ=0.239 (P<0.01).
In males the right/left eye dominance were found respectively as 48 (69.6%), 21 (30.3%) in Gündoan test method as it was found 54 (78.3%), 15 (21.7%) for the same subjects when retested by McManus test. In the males 54 subjects were found with right eye dominance and 15 subjects were found with left eye dominance by McManus test. But only 41 of the 54 subjects were assessed with right eye dominance by the Gündoan test and the rest of 13 were assessed with left eye dominance. According to the McManus method 15 subjects were assessed as they had left eye dominance, but among those only 8 subjects assessed with left eye dominance according to the Gündoan test method. The rest of 7 subjects assessed as they had right eye dominance. According to the Gündoan test 48 subjects were found with right eye dominance, 21 subjects were found with left eye dominance (Table  2).The results of these two tests for male were not related significantly.

　　There was no significant relationship between eye dominance and handedness when compared Gündoan and Oldfield results for the same subjects (Table 3, χ2=0.456).

　　There was also no significant relationship between eye dominance and handedness when compared Gündoan and the McManus  test results (χ2=0.973, P<0.324,Table 4). Although when the same subjects were retested for evaluating hand/eye dominance by the McManus tests a significant relationship were found between hand/eye dominance P<0.05 (Table 4). Furthermore, there was no significant relation between the McManus and the Oldfield tests for evaluating hand/eye dominance (Table 5).

　　The relation between handedness and eye dominance were evaluated by four couple different methods. Appropriate left handednessleft eye dominance ratios were as 46.7%; 56.2%; 50.0%; 46.7% and right handednessright eye dominance ratios were found as 62.2%; 74.2%; 62.6%; 73.2%. On the other hand inappropriate left handednessright eye dominance ratios were found 53.3%; 43.8%; 50.0%; 53.3% and right handednessleft eye dominance ratios were found 37.8%; 25.8%; 37.4%; 26.8% by present study for the same subject. The relationship between handedness[12,16] and eye dominance[11,16] is shown in Table 6.
 
　　The most righthanded subjects were also found to be right eye dominant in all of the tests applied. If used for both of the hand preference and eye dominance analyses. The McManus test seems to be more sensitive than others for determining the right eye dominance in subjects who were lefthanded for throwing. Similar tendency was also occurred for the determination of right eye dominance in subjects with dominant right hand preference. On the other hand, the Gündoan[11] test for the dominant eye was found to have a similar relationship with the hand preference determined by either writing or throwing tasks.

　　DISCUSSION

　　The data considering the relationship between handedness and eye dominances were inconsistent. Dominant eye and hand preference were stated to be related significantly in some studies[5,9,16]. On the other hand there are also statements concerning the absence of any significant relation between eye dominance and hand preference in the literature[4].
　　Methodological diversity concerning these studies which was the main target of the present study seems to be a devastating feature leading to inconsistent results[12,16,1922]. In the present study determined ratios for left handedness was 8.4% by the Oldfield test and it was found 8.9 % by the McManus test and right handedness was 91.6% by the Oldfield test and it was found 91.1% by the McManus test. The detection of handedness in the present study correlates with our previous findings and the literature in terms of right hand preference [1315,21]. The ratio for left eye dominance was found 38.5% by the Gündoan test and it was found 28.5% by McManus test for the same subject. The right eye dominance was found 61.5% by the Gündoan test and it was found 71.5% by the McManus tests which were correlated with our previous findings and the literature in terms of high right eye dominancy[6,8,9,16,22]. These results indicate the reliability of the methods used in the present study for determination of eye dominance and handedness. In the present study consistent left handleft eye dominance ratios of 46.7 %, 56.2 %, 50.0 % 46.7% and right handright eye dominance ratios of 62.2%; 74.2%; 62.6%; 73.2% as shown in Table 6 were found compatible with the previous reports stating 61.0%; 67.6%; 22.0%; 50.0%; 46.6% for the left and 85.0%;85.5%;83.5% for the right, respectively[1,57,22]. Inconsistent handeye preference ratios of 53.3%;43.8%; 50.0%; 53.3% for left handright eye and of 37.8%; 25.8%; 37.4%; 26.8% for right handleft eye were also compatible with the literature considering 67.0%; 50.0%; 53.3%; 40.0% for left handright eye and 11.0%; 10.2%; 10.1%; 53.2 % for right hand left eye [1,57,22]. The discrepancy concerning the incidence of left hand but right eye dominant subjects observed with McManus tests seems to be related with the previous statement considering individuals who were lefthanded for writing but were righthanded for throwing known as inconsistent lefthanders representing 28.8% of lefthanders [2325]. Eyedness was concluded to be more likely related to throwing than to writing hand in the literature. The eye is of fixed mass and in a fixed orbit so that it can be moved remarkably precisely and predictably by such a ballistic mechanism; but that apart, the mechanism is in principle no different from throwing a ball with a hand. If correct, then eyedness should show a clearer and more straight forward relationship with the throwing hand than with the writing hand. In passing, it might be noted that the frontal eye fields, which are important for the control of voluntary saccades, are located only about 20 mm anterior to the sensory motor cortex for the hand [26].

　　In a previous study of Manus et al[16] 28.8% of lefthanded writers and 1.6% of righthanded writers showed inconsistent handedness, preferring to throw with the hand contralateral to their preferred writing hand. These proportions are compatible with the previously reported figures of  Gilbert et al[27] in a massive survey of over one million individuals where, considering the 251881 males and 336483 females who were in the age range 10±40 years in which the incidences of handedness did not vary with age, 32.4% of male and 37.5% of female lefthanded writers threw with their right hand, and 1.55% of male and 1.05% of female righthanded writers threw with their left hand; and with the smaller study of Grimshaw et al[28] where 35.4% of 322 lefthanded writers and 2.25% of 1640 righthanded writers were inconsistent for throwing. We can therefore conclude that crossed writing and throwing hand is a reliable phenomenon in a minority of both lefthanders and righthanders. In the present study, inconsistency considering handedness was 0.5% in left handers and 0.05% in right handers indicating the homogeneity. The Rosenbach[17] and Miles[4] methods were modified by the Gündoan et al[11]which restricted eye, head and hand movements during test period. Many forms of assessment in the measurement of lateralization of eye dominance were contaminated by handedness: thus, for instance, observing the eye used to sight down a rifle may produce a spurious association with handedness due to the rifle typically being held with a finger of the dominant hand on the trigger.
　　Similarly, if a subject is asked to look through a small object such as kaleidoscope, held in one hand, the holding of the object in dominant hand may well distort measures of association between handedness and eye dominance [9]. Additionally eye dominance has sometimes been assessed using questionnaires concerned with monocular activities restriction [29,30].

　　In our study, we applied individual performance test according to Gündoan method for dominant eye assessment without using monocular activities. During this test hand movements were restricted so that eye dominance was not contaminated by dominant handedness. Dominant eye which was stated to be altered according to visual field is being left or right side of the target point restriction [31]. The restricting head movements we prevented shifting visual field during dominant eye assessment. Moreover, when we asked the subjects to close one of their eyes, the deviation distances between near (N) and far (F) points was smaller than in the previous study of Baykal[6]. In addition, deviation distance between N and F points results of our study were more homogenous than Baykals[6] findings. The homogenous measurement of our study seems to confirm the reliability of our method. Right handednessright eye dominance was higher in the majority of our subjects indicating left cerebral hemisphere dominance. Dominant eye and hand preference was shown to be related significantly when the McManus method was applied for determinacy of eye dominances and hand preference (P<0.05, Table 4). This finding correlates with the literature in that the throwing hand is independent from training just like the dominant eye [16].

　　In conclusion, the dominant eye seems to be significantly related to the throwing hand more consistently than the writing hand. Our results support the literature in terms of reflection of life long functional cerebral asymmetry of the brain also via throwing hand besides the dominant eye as it was previously mentioned by other authors[5,15,16]. Future studies investigating the role of inheritance to model properly the interactions between the writing hand the throwing hand, and eye dominance seem to be mandatory.

　　Acknowledgments

　　Do Dr. Ersin ü瘙
塂, Yrd. Do. Dr. Canan Yazc for their excellent statistical studies, Bio.Ayten im瘙
塂ek, Fatih zkul for his technical support during design of the eye dominance measurement device, and our university students for their voluntary participation to our reseach programme and to our medical research group students as Alp Tuna Beksac, Mehmet Emre G naydin, Sema Kurban and Isik Ocak for their excellent assistance during data collection.

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