Physical constraints on mental imagery: proposition of a mental rotation strategy through investigation of side-specific effects of hand posture on hand laterality judgement task perfromance.

Real and imagined movements share many properties and similar conditions affect performance in both. The study of motor imagery has led to a number of findings related to the cognitive aspects of action control. The hand laterality judgment task has been extensively used to investigate factors affecting motor imagery, specifically mental rotation of body parts. Manipulations of this task have revealed that there is an effect of posture of a participant’s hand. This study builds on findings related to effects of posture by looking at the side-specific effect of hand congruency to stimulus view on hand laterality judgement, and uses the findings to propose a likely strategy used by participants in the task. In a fully-crossed design, forty-eight right-handed participants judged the laterality of rotated hand-picture stimuli while adopting four postures: both hands supine; both hands prone; right hand supine, left hand prone; left hand supine, right hand prone. The hypothesis-driven analysis revealed a significant main effect of right congruency and a significant two-way interaction of left congruency on speed of judgements. The position of the right hand appeared to have an overall influence on speed of judgements, and the effect posture of the left hand was contained to left-handed stimuli judgements. This is compatible with a serial strategy where the dominant hand is mentally rotated first to check for a stimulus match before the non-dominant hand. Conditions with both hands congruent resulted in faster reaction times. Performance was most impaired by a congruent hand opposite to the stimulus laterality when the matching hand was incongruent suggesting having the ‘wrong hand’ congruent was misleading. This resulted in a small crossover effect of left hand position on right-handed stimuli. This suggests that although an overall dominant-led serial strategy may be in place, the nature of the stimulus itself also influences approach to the task