'The perception of liquids, particularly water, is a vital sensory function for survival, but little is known about the visual perception of transparent liquids. Here we show that human vision has excellent ability to perceive a transparent liquid solely from dynamic image deformation. No other known image cues are needed for the perception of transparent surfaces. Static deformation is not effective for perceiving transparent liquids. Human vision interprets dynamic image deformation as caused by light refraction at the moving liquid’s surface. Transparent liquid is well perceived from artificial image deformations, which share only basic flow features with image deformations caused by physically correct light refraction.'

Perceptual transparency from image deformation

Takahiro Kawabe,1 Kazushi Maruya, and Shin’ya Nishida

Analysis of the human perception of water and the refraction of light that creates image distortion.