Left-handers’ struggle in a rightward wor(l)d: The relation between horizontal spatial bias and effort in directed movements

ABSTRACT

Five studies investigated the role of handedness and effort in horizontal spatial bias related to agency (Spatial Agency Bias, SAB). A Pilot Study (n = 33) confirmed the basic assumption that rightward writing requires greater effort from left- than from right-handers. In three studies, Italian students (n = 591 right-handed, n = 115 left-handed) were found to start drawings on the left, proceeding rightward (Study 1a, 1b), and to draw moving objects with a rightward orientation in line with script direction (Study 1c). These spatial asymmetries were displayed stronger by left- than by right-handed primacy school children, arguably due to the greater effort involved in learning how to write in a rightward fashion. Once writing has become fully automatic (high school) right- and left-handed students showed comparable spatial bias (Study 1c). The hypothesized role of effort was tested explicitly in Study 2 in which 99 right-handed adults learned a new (leftward) spatial trajectory through an easy or difficult motor exercise. The habitual rightward bias was reliably reduced, especially among those who performed a difficult task requiring greater effort. Together, findings are largely in line with the body specificity hypothesis (Casasanto, 2011) and suggest that spatial asymmetries are learned and unlearned most efficiently through effortful motor exercises.

KEYWORDS:

• Handedness
• body specificity
• horizontal spatial bias
• script direction
• visual perception
• asymmetry

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1 The spatial orientation of objects with handles is generally explained on the bases of affordances related to grasping (e.g., Tucker & Ellis, 1998).

2 Perceptual tasks should not be entirely immune to the influence of handedness given that imagery is, in part, under the influence of the motor system (see body specificity hypothesis, Casasanto, 2011, and motor imagery theory, Martin & Jones, 1999)

3 Although separate analyses for each data collection are problematic due to small numbers of left-handed children, the inspection of frequencies reveals in all three cases a stronger tendency to draw scenes from left to right among left-handed than among right-handed children.

4 Elementary school students also completed two additional tasks at the end of the questionnaire, namely a line bisection task (leading to a general leftward bias) and a task of spatial organization of three pictures of a target during childhood, adulthood and old age (confirming that age is mapped onto space in a left-to-right fashion). Given that these two tasks where included for different scopes and were not affected by participants’ handedness or age, they will not be further discussed.

5 Since the valence of the interaction did not affect the results, this variable will not be discussed further.

Additional information

Funding

This research was funded by a PRIN Grant (on “Embodiment and Social Cognition: The Role of Sensomotory Processes in the Perception of Individuals and Groups,” 2008, no. 20082YHWHB) from the Italian Ministry of Education, University, and Research.