Mental rotation of letters, body parts and scenes during whole-body tilt: Role of a body-centered versus a gravitational reference frame

• Published in: Human movement science 2015-04, Vol.40, p.352-358
• Main Authors: Bock, Otmar L., Dalecki, Marc
• Format: Article
• Language: English
• Subjects: Adult; Body tilt; Cognitive processing; Depth Perception; Embodiment; Female; Gravitation; Human Body; Humans; Male; Mental rotation; Normal Distribution; Orientation; Photic Stimulation; Posture; Reaction Time; Reference frame; Rotation; Vision, Ocular; Writing; Young Adult
• ISSN: 0167-9457; 1872-7646
• DOI: 10.1016/j.humov.2015.01.017

•We explored the reference frame and endpoint of three typical mental rotation tasks.•To elucidate if the reference frame is based on a gravity or body-centered vertical.•Subjects were tested in upright and 60° whole-body tilted left shoulder down position.•Subjects used the same reference frame for letter, hand and own body rotation.•At 60° tilt the rotation endpoint shifted 12° from gravity towards the body reference. It is known that in mental-rotation tasks, subjects mentally transform the displayed material until it appears “upright” and then make a judgment. Here we evaluate, by using three typical mental rotation tasks with different degrees of embodiment, whether “upright” is coded to a gravitational or egocentric reference frame, or a combination of both. Observers stood erect or were whole-body tilted by 60°, with their left ear down. In either posture, they saw stimuli presented at different orientation angles in their frontal plane: in condition LETTER, they judged whether the stimuli were normal or mirror-reversed letters, in condition HAND whether they represented a left or a right hand, and in condition SCENE whether a weapon laid left or right in front of a displayed person. Data confirm that reaction times are modulated by stimulus orientation angle, and the modulation curve in LETTER and HAND differs from that in SCENE. More importantly, during 60° body tilt, the modulation curve shifted 12° away from the gravitational towards the egocentric vertical reference; this shift was comparable in all three conditions and independent of the degree of embodiment. We conclude that mental rotation in all conditions relied on a similar spatial reference, which seems to be a weighted average of the gravitational and the egocentric vertical, with a higher weight given to the former.