FOOT AND EYE PREFERENCES IN ADULTS: RELATIONSHIP WITH HANDEDNESS, SEX AND AGE Catherine Dargent-Pare, Maria De Agostini, Mounir Mesbah and Georges Dellatolas (INSERM Ul69, Villejuif, France)
INTRODUCTION
Asymmetry of function could be considered as less pronounced for human foot and eye than for hand, as both feet contribute to locomotion a.nd both eyes to visual function. Nevertheless, human foot and eye preferences, which can be easily assessed with questionnaires in normal adults (Chapman, Chapman and Allen, 1987; Coren and Porac, 1978) do exist (Peters, 1988; Porac and Coren, 1976). Their relationships with handedness is controversial, particularly for eye preference (Rymar et aI., 1984; Swiercinsky, 1977; Teng et aI., 1978; Van Camp and Bixby, 1977), and their relationships with other aspects of cerebral lateralization need further studies (Costeff et al., 1988; Peters, 1988). Sex and age effects in adult handedness have been repeatedly found (Annett, 1985; Bryden, 1977; Fleminger, Dalton and Standage, 1977; Salmaso and Longoni, 1985). We have recently (Dellatolas et aI., 1991) confirmed previous reports (Maehara et al., 1988; Porac and Coren, 1981) of a systematic increase of the strong right-handers/mixed right-handers ratio with age in normal adults. Coren, Porac and Duncan (1981) have reported a similar age effect for foot and eye preferences, but this finding was not replicated by others (Rymar et al., 1984; Van Camp and Bixby, 1977). The purpose of this paper is to examine the relationship between handedness and foot and eye preferences in large samples of normal adult populations from five different countries, and to investigate if the sex and age effects observed in handedness also exist for foot and eye preferences. MATERIALS AND METHOD
Subjects Participants were 2639 males and 2560 females, mainly students and employees, aged 15 or more, from five countries: Algeria (N = 682), Greece (N = 703), Italy (N = 710), Spain (N = 737) and France (N = 2367), unselected for handedness. Age distribution differed strongly according to the country: in Algeria there were no subjects older than 35 years of age; 74"'0 of the subjects in Spain, but only 6.6"'0 in France, were under 25. Age was not related to socio-economic status, and there were not illiterate subjects. Cortex, (1992) 28, 343-351
344
C. Dargent-Pare and Others
Tests and Procedure Handedness Assessment
Twelve handedness items, selected from the results of a previous study conducted in a French sample (Dellatolas et ai., 1988), were used: the hand used for writing, drawing, throwing, playing tennis, shaving or applying makeup, brushing one's teeth, cutting bread, hammering, turning a screwdriver, lighting a match, combing one's hair and eating with a spoon. The handedness items were multiple choice questions with 3 possible answers: "right hand", "both hands" or "left hand", coded 1,2 and 3 respectively. The two items with the lowest loadings on the first factor of a Principal Component Analysis were excluded: "comb" and "match" in Algeria and "writing" and "drawing" in the 4 other countries (Nedjar et ai., 1989; Dellatolas et ai., 1991). A handedness score (HS) was computed as the sum of the answers to the 10 items. HS ranged between 10, corresponding to the answer "right hand" to all 10 items, and 30, corresponding to the answer "left hand" to all 10 items. Subjects were classified as Right-handers (RH) if their HS was less than 20 (midinterval), and as Left-handers (LH) if their HS was 20 or greater. Foot and Eye Preference Assessment
The foot preference question was: "which foot do you kick a ball with?" The eye preference question was: "which eye do you aim at a target with, when the other eye is closed?" The 3 possible answers for each item were: "right", "either" or "left". According to Coren and Porac (1978), these items are reliable (good agreement between self-reports at retest), and valid (good agreement between self-report and behavior). The strong intercorrelations between several foot preference and eye sighting dominance items and tests proposed (Chapman et ai., 1987; Hebben et aI., 1981; Porac et ai., 1980), allow the choice of only one item in large epidemiological surveys. Statistical Methods
Due to missing data, only 5064 subjects (97.4070 of the initially survied) were included in the analysis. Hierarchical log-linear models were used. The search of the log-linear model "best" fitting the data was performed by a backward elimination method, using the Hiloglinear procedure of SPSSX. Two separate analysis, one for footedness and the other for eyedness, were performed. In each one, the following variables were included: foot or eye (three levels: "right", "either", "left"), handedness (two levels: right- and left-handers), sex, age group (three levels: less than 25 y, 25-35 y, more than 35 y), and country (five levels). Only interactions including foot or eye preference with the other variables will be discussed. Results will be illustrated by presenting marginal tables of the hand-foot and hand-eye interactions (with corresponding Odds-Ratios and p-values of marginal chi-squares) in each country by sex group, in each age group, and for right-handers in each country by age group.
RESULTS
Foot Preference
The log-linear model retained only two interactions including foot preference: Foot by Hand by Sex (maximum likelihood chi-square = 53.1, d.f. = 2, p
INTRODUCTION
Asymmetry of function could be considered as less pronounced for human foot and eye than for hand, as both feet contribute to locomotion a.nd both eyes to visual function. Nevertheless, human foot and eye preferences, which can be easily assessed with questionnaires in normal adults (Chapman, Chapman and Allen, 1987; Coren and Porac, 1978) do exist (Peters, 1988; Porac and Coren, 1976). Their relationships with handedness is controversial, particularly for eye preference (Rymar et aI., 1984; Swiercinsky, 1977; Teng et aI., 1978; Van Camp and Bixby, 1977), and their relationships with other aspects of cerebral lateralization need further studies (Costeff et al., 1988; Peters, 1988). Sex and age effects in adult handedness have been repeatedly found (Annett, 1985; Bryden, 1977; Fleminger, Dalton and Standage, 1977; Salmaso and Longoni, 1985). We have recently (Dellatolas et aI., 1991) confirmed previous reports (Maehara et al., 1988; Porac and Coren, 1981) of a systematic increase of the strong right-handers/mixed right-handers ratio with age in normal adults. Coren, Porac and Duncan (1981) have reported a similar age effect for foot and eye preferences, but this finding was not replicated by others (Rymar et al., 1984; Van Camp and Bixby, 1977). The purpose of this paper is to examine the relationship between handedness and foot and eye preferences in large samples of normal adult populations from five different countries, and to investigate if the sex and age effects observed in handedness also exist for foot and eye preferences. MATERIALS AND METHOD
Subjects Participants were 2639 males and 2560 females, mainly students and employees, aged 15 or more, from five countries: Algeria (N = 682), Greece (N = 703), Italy (N = 710), Spain (N = 737) and France (N = 2367), unselected for handedness. Age distribution differed strongly according to the country: in Algeria there were no subjects older than 35 years of age; 74"'0 of the subjects in Spain, but only 6.6"'0 in France, were under 25. Age was not related to socio-economic status, and there were not illiterate subjects. Cortex, (1992) 28, 343-351
344
C. Dargent-Pare and Others
Tests and Procedure Handedness Assessment
Twelve handedness items, selected from the results of a previous study conducted in a French sample (Dellatolas et ai., 1988), were used: the hand used for writing, drawing, throwing, playing tennis, shaving or applying makeup, brushing one's teeth, cutting bread, hammering, turning a screwdriver, lighting a match, combing one's hair and eating with a spoon. The handedness items were multiple choice questions with 3 possible answers: "right hand", "both hands" or "left hand", coded 1,2 and 3 respectively. The two items with the lowest loadings on the first factor of a Principal Component Analysis were excluded: "comb" and "match" in Algeria and "writing" and "drawing" in the 4 other countries (Nedjar et ai., 1989; Dellatolas et ai., 1991). A handedness score (HS) was computed as the sum of the answers to the 10 items. HS ranged between 10, corresponding to the answer "right hand" to all 10 items, and 30, corresponding to the answer "left hand" to all 10 items. Subjects were classified as Right-handers (RH) if their HS was less than 20 (midinterval), and as Left-handers (LH) if their HS was 20 or greater. Foot and Eye Preference Assessment
The foot preference question was: "which foot do you kick a ball with?" The eye preference question was: "which eye do you aim at a target with, when the other eye is closed?" The 3 possible answers for each item were: "right", "either" or "left". According to Coren and Porac (1978), these items are reliable (good agreement between self-reports at retest), and valid (good agreement between self-report and behavior). The strong intercorrelations between several foot preference and eye sighting dominance items and tests proposed (Chapman et ai., 1987; Hebben et aI., 1981; Porac et ai., 1980), allow the choice of only one item in large epidemiological surveys. Statistical Methods
Due to missing data, only 5064 subjects (97.4070 of the initially survied) were included in the analysis. Hierarchical log-linear models were used. The search of the log-linear model "best" fitting the data was performed by a backward elimination method, using the Hiloglinear procedure of SPSSX. Two separate analysis, one for footedness and the other for eyedness, were performed. In each one, the following variables were included: foot or eye (three levels: "right", "either", "left"), handedness (two levels: right- and left-handers), sex, age group (three levels: less than 25 y, 25-35 y, more than 35 y), and country (five levels). Only interactions including foot or eye preference with the other variables will be discussed. Results will be illustrated by presenting marginal tables of the hand-foot and hand-eye interactions (with corresponding Odds-Ratios and p-values of marginal chi-squares) in each country by sex group, in each age group, and for right-handers in each country by age group.
RESULTS
Foot Preference
The log-linear model retained only two interactions including foot preference: Foot by Hand by Sex (maximum likelihood chi-square = 53.1, d.f. = 2, p
