Leftward Deviation and Asymmetric Speed of Egocentric Judgment between Left and Right Visual Fields.

Ying Zhou,Bing Li,Yujun Pan,Gang Wang,Mingsha Zhang

doi:10.3389/fnins.2017.00364

Abstract

The egocentric reference frame is essential for body orientation and spatial localization of external objects. Recent neuroimaging and lesion studies have revealed that the right hemisphere of humans may play a more dominant role in processing egocentric information than the left hemisphere. However, previous studies of egocentric discrimination mainly focused on assessing the accuracy of egocentric judgment, leaving its timing unexplored. In addition, most previous studies never monitored the subjects' eye position during the experiments, so the influence of eye position on egocentric judgment could not be excluded. In the present study, we systematically assessed the processing of egocentric information in healthy human subjects by measuring the location of their visual subjective straight ahead (SSA) and their manual reaction time (RT) during fixation (monitored by eye tracker). In an egocentric discrimination task, subjects were required to judge the position of a visual cue relative to the subjective mid-sagittal plane and respond as quickly as possible. We found that the SSA of all subjects deviated to the left side of the body mid-sagittal plane. In addition, all subjects but one showed the longest RT at the location closest to the SSA; and in population, the RTs in the left visual field (VF) were longer than that in the right VF. These results might be due to the right hemisphere's dominant role in processing egocentric information, and its more prominent representation of the ipsilateral VF than that of the left hemisphere.

Highlights

Even though the external objects can be represented in multiple reference frames (Goodale and Milner, 1992; Olson, 2003; Burgess, 2006; Milner and Goodale, 2008; Land, 2012; Boccia et al, 2014), the egocentric reference frame is the most fundamental one (Filimon, 2015)
Patients with right hemisphere damage more frequently show egocentric neglect of the contralesional hemispace (Beis et al, 2004; Ringman et al, 2004; Becker and Karnath, 2007; Kleinman et al, 2007), as well as an ipsilesional deviation of the subjective straight ahead (SSA) (Karnath, 1994; Farne et al, 1998; Ferber and Karnath, 1999; Schindler and Kerkhoff, 2004; Richard et al, 2004a,b, 2005; Saj et al, 2006; Rousseaux et al, 2013). These findings reveal that the processing of egocentric information is asymmetrically distributed between the two hemispheres, with the right hemisphere playing a more dominant role
The inconsistent judgment occurred more frequently when the visual cue was close to the body mid-sagittal plane

Summary

Introduction

Even though the external objects can be represented in multiple reference frames (Goodale and Milner, 1992; Olson, 2003; Burgess, 2006; Milner and Goodale, 2008; Land, 2012; Boccia et al, 2014), the egocentric reference frame is the most fundamental one (Filimon, 2015). Patients with right hemisphere damage more frequently show egocentric neglect of the contralesional hemispace (Beis et al, 2004; Ringman et al, 2004; Becker and Karnath, 2007; Kleinman et al, 2007), as well as an ipsilesional deviation of the SSA (Karnath, 1994; Farne et al, 1998; Ferber and Karnath, 1999; Schindler and Kerkhoff, 2004; Richard et al, 2004a,b, 2005; Saj et al, 2006; Rousseaux et al, 2013). Studies of SSA in healthy subjects showed controversial results (Jeannerod and Biguer, 1989; Karnath et al, 1994, 2002; Chokron and Imbert, 1995; McCourt et al, 1997; Vallar et al, 1999; Richard et al, 2004a,b; Saj et al, 2006, 2013; Sumitani et al, 2007; Reinersmann et al, 2012; Rousseaux et al, 2013)

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Discussion

Conclusion