Imagined paralysis impairs embodied spatial transformations

Abstract

Recent studies showed that motor deficits and limb amputations selectively impair mental rotation of respective body parts. This is due to modifications in the body schema, which plays a pivotal role in bodily related mental spatial transformations. In the present study, we investigated whether imagined paralysis could affect mental transformations in healthy participants. Participants were required to make leg laterality judgments of imitable and non-imitable body postures that were presented at different orientations. Mental spatial transformation of imitable body posture relies on emulation processes, a mechanism through which the posture is covertly imitated by the observer. Imagined paralysis selectively impaired mental transformation of imitable body postures. These results reflect an inability to fully emulate stimulus postures, suggesting a modulation in the body schema. Our results show that the body schema incorporates top-down information about motoric constraints which can influence embodied cognition in healthy participants.

Keywords:

• Embodiment
• Imagery
• Body schema
• Mental transformation; Paralysis

Acknowledgments

The study was funded by the Swiss National Science Foundation (Pro*Doc grant PDFMP1_127238 and Sinergia grant CRSII1-125135/1). We would like to thank Damaris Bachmann, Cora Bobst, and Nora Preuss for assistance in data collection.

Notes

¹Some studies report laterality effects as a function of handedness for mental spatial transformation of body parts (e.g., Nico et al., 2004). To investigate possible effects of laterality in the present data, the same analysis of RTs was performed with the additional between-variable laterality of the bent leg (left vs. right). This analysis shows that right-handed participants needed less time for correct judgments when the right leg was bent (M = 1397 ms, SD = 579 ms) as compared to the left leg (M = 1427 ms, SD = 580 ms), F(1, 38) = 4.27, MSE = 0.009, p = .046. This supports the observation by Nico et al. (2004) that participants use a strategy in which they initially mentally simulate movements of their dominant limb, which is the right leg in most right-handed people (Brown & Taylor, 1988). Laterality of the bent leg also interacted with angle of rotation, F(4, 152) = 3.16, MSE = 0.005, p = .016. Post hoc test showed that the difference between the left and right leg was significant only for 0°. All other interactions with laterality of the bent leg were not significant (p > .12). The small number of left-handed participants in our sample (n = 3) does not permit conclusions about the effect of handedness of the participants.