I am intrigued by this study so back to comment again. I would think being able to position something vertically is related to our sense of gravity. Gravity is the one constant we all have in our sensorimotor development so it is interesting to find a set of circumstances where it is skewed. Also, noted that in the dental chair the head is supported while on the tram it is not. Wonder if that makes a difference.

My thoughts on where this is applicable is with children with significant motor development who are in wheelchairs, often reclined and are then pushed by others. Or those that can use a power chair but are in slightly reclined position. They may be better off if they can tolerate a more upright position (maybe a new health insurance justification for more therapy). They would be in this circumstance longer than someone on a tram, usually a whole school day once they are school age. I wonder if there is a lasting impact on their relationship/experience of gravity and the vertical.

Anyway, just some thoughts I had. Thanks for posting the study.