Applying the Gestalt theory of grouping and perception, Tusi proposes a question of local and global motion perception. The global perception creates the optical illusion of a circular shape made up of spheres rotating and rolling over its centre, whereas the local perception is that each sphere moves along its own straight rectilinear path.
The presence of a singular red point amongst the others allows the viewer to access and realise the principle behind Tusi’s optical illusion.
Tusi shows how perceptual processes work: organising the information from a global structure towards a more fine-grained analysis. The identification of global structures being useful for the reduction of those stimuli to local structures.