Visual Worlds 2/The Raft

The raft is suspended by a wire and appears to float in space.
The brain has parallel visual systems to recognise objects, and to enable spatial action. The visual perception is usually simple and straight-forward. Recognising objects and identifying their possible use, weight and point of gravity, rarely poses any problems.
The raft, however, perplexes the parallel visual systems. It takes time to comprehend the situation. What is the platform for, why does it appear to hover freely, and where is its point of gravity?