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

Chiara Lucafò,Lucia Pelosi Zazzerini,Luca Tommasi,Gianluca Malatesta,Ilaria Amodeo,Caterina Padulo,Daniele Marzoli,Stefano Troiano

doi:10.3390/sym13081349

Abstract

Both static and dynamic ambiguous stimuli representing human bodies that perform unimanual or unipedal movements are usually interpreted as right-limbed rather than left-limbed, suggesting that human observers attend to the right side of others more than the left one. Moreover, such a bias is stronger when static human silhouettes are presented in the RVF (right visual field) than in the LVF (left visual field), which might represent a particular instance of embodiment. On the other hand, hemispheric-specific rotational biases, combined with the well-known bias to perceive forward-facing figures, could represent a confounding factor when accounting for such findings. Therefore, we investigated whether the lateralized presentation of an ambiguous rotating human body would affect its perceived handedness/footedness (implying a role of motor representations), its perceived spinning direction (implying a role of visual representations), or both. To this aim, we required participants to indicate the perceived spinning direction (which also unveils the perceived handedness/footedness) of ambiguous stimuli depicting humans with an arm or a leg outstretched. Results indicated that the lateralized presentation of the stimuli affected both their perceived limb laterality (a larger number of figures being interpreted as right-limbed in the RVF than in the LVF) and their perceived spinning direction (a larger number of figures being interpreted as spinning clockwise in the LVF than in the RVF). However, the hemifield of presentation showed a larger effect size on the perceived spinning direction than on the perceived limb laterality. Therefore, as we already proposed, the implicit representation of others’ handedness seems to be affected more by visual than by motor processes during the perception of ambiguous human silhouettes.

Highlights

In recent studies [1,2,3,4], we found that when right- and left-handed subjects were required to indicate the orientation of ambiguous 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 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]
From an evolutionary point of view, an attentional and perceptual bias in favor of right-handed movements might be adaptive in social life because most everyday social interactions occur with right- rather than left-handed individuals

Summary

Introduction

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 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]. The present study investigated whether the lateralized presentation of an ambiguous rotating human body affects its perceived handedness/footedness (in which case, mainly motor representations would be involved) or its perceived spinning direction (in which case, mainly visual representations would be involved), or both To this aim, we used rotating stimuli depicting humans performing unimanual or unipedal movements

Participants

Stimuli

Procedure

Schematic

Data Analysis

Results