The effects of sex and handedness on masturbation laterality and other lateralized motor behaviours

Figures & data

Figure 1. Image used in kissing question.

Note: The figure indicates the labels shown to participants to ask them which cheek of an emotionally close person they would kiss, with left-right labels reflecting the viewer’s perspective.

Figure 2. Jittered density plot for Edinburgh Handedness Inventory scores.

Note: To facilitate comparisons across measures, the modified Edinburgh Handedness Inventory (EHI) score was calculated using means across the ten items, expressed here on a scale of −100 (always left) through 0 (both hands equally) to 100 (always right). Data show raw scores as a function of handedness and sex. Bars indicate standard deviations with means represented by dots in their centre.

Figure 3. Jittered density plot for footedness.

Note: To facilitate comparisons across measures, footedness was calculated using means across the three items, expressed here on a scale of −100 (always left) through 0 (both feet equally) to 100 (always right). Data show raw scores as a function of handedness and sex. Bars indicate standard deviations with means represented by dots in their centre.

Figure 4. Jittered density plot for eyedness.

Note: To facilitate comparisons across measures, eyedness was calculated using means across the three items, expressed here on a scale of −100 (always left) through 0 (both hands equally) to 100 (always right). Data show raw scores as a function of handedness and sex. Bars indicate standard deviations with means represented by dots in their centre.

Figure 5. Hand use for masturbation.

Note: Percentage observations as a function of sex and handedness of responses to the three masturbation laterality questions “If you masturbate please indicate which hand you typically use”; “If your hands are not holding anything else, please indicate which hand you typically use to masturbate”, and “If you hold a sex aid to masturbate, such as a vibrator, please indicate which hand you typically use”. Totals do not always add to 100% due to rounding.

Figure 6. Cheek kissing preference.

Note: Percentage observations of responses to the kissing cheek laterality question, with the left cheek and right cheek being expressed from the perspective of the viewer, as shown in Figure 1. Totals do not always add to 100% due to rounding.

Figure 7. Frequency of masturbation.

Note: Percentage observations of responses to the masturbation frequency question. Abbreviations: / m = per month; / w = per week, 8+ = more than 8 times. Totals do not always add to100% due to rounding.

Table 1. Means and SDs per measure per condition.

Group	Female Left-handed		Female Right-handed		Male Left-handed		Male Right-handed		Total
Statistic	Mean	SD	Mean	SD	Mean	SD	Mean	SD	Mean	SD
EHI	−59.86	36.50	82.02	18.13	−57.43	34.04	83.80	15.86	11.42	76.10
Foot	−16.51	49.00	50.33	29.01	−16.17	56.73	47.64	32.39	16.01	54.20
Eye	−26.83	64.90	35.62	52.97	−30.33	67.14	38.55	54.80	3.94	68.49
Kiss	−22.86	55.48	7.35	56.90	−21.50	55.17	11.11	53.72	−6.65	57.35
Masturbate typical hand	−46.46	65.17	65.43	47.53	−35.05	72.23	66.84	59.61	12.11	81.78
Masturbate not holding anything else	−46.39	66.63	70.21	45.39	−38.66	71.63	68.88	56.77	13.21	82.77
Masturbate sex aid	−41.56	66.10	67.72	41.63	−28.13	62.14	31.82	71.61	10.41	76.31
Masturbate Frequency	2.37	2.05	2.35	1.96	4.96	2.93	4.79	2.75	3.59	2.75

Note: EHI = modified Edinburgh Handedness Inventory score. All scales except Masturbation Frequency are expressed on a −100–100 scale, −100 = always left, −50 = usually left, 0 = both equally, 50 = usually right, 100 = always right. Masturbation Frequency over the last month was measured on ordinal scale: 0 = Not at all in the past month, 1 = Once in the past month, 2 = Two or three times in the past month, 3 = Around once a week, 4 = Around twice a week, 5 = around three times a week, 6 = around four times a week, 7 = around five times a week, 8 = around six times a week, 9 = around seven times a week, 10 = around eight times or more a week.

Table 2. Strength of hand preference.

	Left-handed		Right-handed		Mann-Whitney test				Effect size
	Mean	SD	Mean	SD	U	NL, NR	Z	p	d
EHI	59.33	34.06	82.86	17.00	11988.0	204, 202	7.34	< .001	0.87
Foot	16.58	52.80	48.93	30.61	13277.5	204, 202	6.25	< .001	0.75
Eye	29.17	65.41	37.38	53.81	19665.5	204, 202	0.81	0.418	0.14
Kiss Cheek	22.55	55.10	9.41	55.19	17811.5	204, 202	2.48	0.013	0.24
Masturbate typical hand	40.77	68.99	65.54	54.41	15013.5	195, 193	3.75	< .001	0.40
Masturbate holding nothing else	42.49	69.28	68.91	51.97	14642.5	193, 193	4.00	< .001	0.43
Masturbate sex aid	37.50	65.25	56.19	55.15	5151.5	108, 113	2.12	0.034	0.31

Note: Means, standard deviations, and outcomes of Mann-Whitney tests. Abbreviations: EHI = Modified Edinburgh Handedness Inventory score, N_L = N_left-handers, N_R = N_{right-handers},; Mean values refer to mean absolute distances away from the neutral “both equally” point, set to zero for this analysis.

Table 3. Correlation Matrix for masturbation and other behaviours.

	EHI	Foot	Eye	Kiss Cheek
Foot	0.680	–
Eye	0.475	0.439	–
Kiss Cheek	0.259	0.202	0.216	–
Masturbate	0.630	0.512	0.344	0.183

Note: EHI = modified Edinburgh Handedness Inventory score. The correlation coefficients are Spearman’s rho. For all, p < .001.

Data availability

Supplemental data for this article can be accessed at: https://doi.org/10.6084/m9.figshare.16912966.v1.