The Bias toward the Right Side of Others Is Stronger for Hands than for Feet

Abstract

As shown by a series of previous studies, ambiguous human bodies performing unimanual or unipedal actions tend to be perceived more frequently as right-handed or right-footed rather than left-handed or left-footed, which indicates a perceptual and attentional bias toward the right side of others’ body. However, none of such studies assessed whether the relative strength of such a bias differs between the upper and lower limbs. Indeed, given that the prevalence of right-handedness is slightly larger than that of right-footedness, and given that hands provide more information than feet as regards both communicative and aggressive acts, it is plausible that the bias toward the right side of human bodies should be stronger for the hand than for the foot. We performed three experiments in each of which participants had to indicate the rotating direction (revealing the perceived handedness/footedness) of ambiguous human figures with either one limb (arm or leg) or two limbs (one arm and the contralateral leg) extended. The hypothesized advantage of the right hand over the right foot was found in both the second and the third experiment.

Hemifield-Specific Rotational Biases during the Observation of Ambiguous Human Silhouettes

“…Results indicated that the lateralized presentation of the stimuli affected both their perceived limb laterality and their perceived spinning direction, although the effect size was larger in the latter (ηp 2 = 0.06) than in the former (ηp 2 = 0.12) case. In line with our previous studies with ambiguous human silhouettes [1][2][3][4][5][6], with the exception of one out of three experiments in [6], the participants' laterality score did not correlate with the percentage ) compared with male participants (M = 35.73%; t 46 = 2.858, p = 0.026) in the RVF, and no difference was observed between male and female participants in the number of figures interpreted as spinning CW in any of the remaining combinations of hemifield of presentation and outstretched limb (all p > 0.22; Supplementary Material Table S8). Finally, female participants showed a statistical trend to perceive a larger number of CW-spinning figures in the leg-outstretched version of the experiment (M = 56.26%) than in the arm-outstretched version of the experiment (M = 40.03%; t 47 = 2.460, p = 0.070) in the RVF, and no difference was observed between the arm-and leg-outstretched version of the experiment in the number of figures interpreted as spinning CW in any of the remaining combinations of hemifield of presentation and participant's sex (all p > 0.08; Supplementary Material Table S9).…”

“…Results indicated that the lateralized presentation of the stimuli affected both their perceived limb laterality and their perceived spinning direction, although the effect size was larger in the latter (η p 2 = 0.06) than in the former (η p 2 = 0.12) case. In line with our previous studies with ambiguous human silhouettes [1][2][3][4][5][6], with the exception of one out of three experiments in [6], the participants' laterality score did not correlate with the percentage of figures interpreted as right-limbed or spinning CW.…”

“…In recent studies [1][2][3][4], we found that when right-and left-handed subjects were required to indicate the orientation of ambiguous (in terms of front or back view) figures representing human silhouettes in the act of performing one-handed manual actions, both groups reported perceiving the figures more frequently as oriented consistently with a right-handed movement than with a left-handed movement. Similar findings were reported for dynamic stimuli representing ambiguous human bodies represented in the act of performing unimanual and unipedal movements [3,5,6]. These results indicate an attentional/perceptual bias toward the right side of the human body and are also consistent with findings from research investigating the perception of sport actions, according to which the outcomes of right-limbed movements can be anticipated better than the outcomes of leftlimbed movements [7][8][9][10][11][12][13].…”

“…Then, we decomposed each original animation into its 32 constituent frames and created 64 different versions, each of which depicted a complete rotation of the silhouette, by reorganizing the 32 frames on the basis of starting frame and order (i.e., from the 1st to the 32nd and vice versa, from the 2nd to the 1st and vice versa, and so on). Such an order manipulation permitted to offset any association between spinning direction and outstretched arm/leg by including two rotation conditions (e.g., see [3,5,6]). In the first condition, the silhouette turns inward (i.e., "palmward" with reference to the hand movement and "en dedans"-a term describing a spin in which the ballet dancer turns toward the supporting leg-with reference to the foot movement).…”

Human Lateralization, Maternal Effects and Neurodevelopmental Disorders

“…On the other hand, right-handedness might also be fostered by children imitating adult's manual preferences (Fagard and Lemoine, 2006). Similar mechanisms might be involved not only in the development of handedness, but also in the attentional bias toward the right side of others' body observed in both right-and left-handers (Marzoli et al, 2015(Marzoli et al, , 2017a(Marzoli et al, ,b, 2019Lucafò et al, 2016Lucafò et al, , 2021; see also Marzoli et al, 2014), which in turn could account for the left-handers' advantage in fighting and sports (e.g., Groothuis et al, 2013). Although the relative weight of genetic and environmental determinants of handedness has not been established yet, epigenetic effects have been hypothesized at both the molecular (Leach et al, 2014) and the behavioral level (Schmitz et al, 2017), and the same should be true for other instances of functional asymmetries.…”