Trunk-based left/right judgment tasks: experimental investigations of the mechanisms underpinning performance

The process of recognising the laterality of an image depicting a hand (i.e. is a depicted hand a left hand or a right hand?) has been long considered to require motor imagery (MI) of the viewer’s corresponding limb. In recent years, these so-called left/right judgment tasks (LRJTs) have been adopted in clinical practice and extended to involve other body parts (e.g. shoulders, knees, neck, trunk). However, unlike images of hands (and feet), the ability of these other LRJTs to elicit MI is uncertain. For example, trunk-based LRJTs have been introduced into clinical practice for the management of low back pain (LBP) with the assumption that these tasks elicit MI of lateralised trunk movements, a situation that would see the tasks have therapeutic value. However, evidence to support this situation is currently lacking. This thesis presents a series of studies investigating whether MI of lateralised trunk movements is elicited by trunk-based LRJTs. The mechanisms underlying trunk-based LRJTs were investigated by adapting previous experimental approaches that were successful in demonstrating that hand-based LRJTs elicit MI. The first two experiments (Chapters 2 and 3) examined the effect of images depicting postures requiring different amplitudes of movement on the response time (RT) of related judgments. The third experiment (Chapter 4) examined the impact of participants assuming different trunk postures on trunk-based LRJT performance. Finally, experiment 4 (Chapter 5) examined LRJT performance in a group of people with LBP. Results from all 4 experiments consistently failed to support the ability of trunk-based LRJTs to elicit MI of lateralised trunk movement. The findings threaten the validity of using trunk-based LRJTs for their intended purpose in clinical practice