Mental rotation task of hands: differential influence number of rotational axes

Abstract

Various studies on the hand laterality judgment task, using complex sets of stimuli, have shown that the judgments during this task are dependent on bodily constraints. More specific, these studies showed that reaction times are dependent on the participant's posture or differ for hand pictures rotated away or toward the mid-sagittal plane (i.e., lateral or medial rotation, respectively). These findings point to the use of a cognitive embodied process referred to as motor imagery. We hypothesize that the number of axes of rotation of the displayed stimuli during the task is a critical factor for showing engagement in a mental rotation task, with an increased number of rotational axes leading to a facilitation of motor imagery. To test this hypothesis, we used a hand laterality judgment paradigm in which we manipulated the difficulty of the task via the manipulation of the number of rotational axes of the shown stimuli. Our results showed increased influence of bodily constraints for increasing number of axes of rotation. More specifically, for the stimulus set containing stimuli rotated over a single axis, no influence of biomechanical constraints was present. The stimulus sets containing stimuli rotated over more than one axes of rotation did induce the use of motor imagery, as a clear influence of bodily constraints on the reaction times was found. These findings extend and refine previous findings on motor imagery as our results show that engagement in motor imagery critically depends on the used number of axes of rotation of the stimulus set.

Fig. 1

Shown are all used hand stimuli for Set-1: upper row, left column; Set-2: upper row; Set-3: all stimuli. Angles within stimuli represent in-plane angular disparity and angles displayed in the ‘in-depth’ column represent in-depth angular disparity

Fig. 2

Reaction times for all three sets, mirrored at 180° (i.e., 60° represents average RT for 60° and 300° rotated hand stimuli). Error-bars indicate standard error of the mean (SEM)

Fig. 3

Reaction times for all 3 Sets divided into lateral rotation and medial rotation. Lateral rotation indicates rotations away from the mid-sagittal plane, and medial rotation indicates rotations toward the mid-sagittal plane. As can be seen, the significant interaction of Set by DOR (P < 0.01) as represented by the differences in RTs between lateral and medial rotation (i.e., DOR) increases with increasing number of axes of rotation. * indicate significance at the P < 0.05 level, ** indicate significance at the P < 0.01 level. Error-bars indicate standard error of the mean (SEM)