Simple and intriguing examples for nonlinear dynamics in visual perception are presented by means of optical illusions. Well known visual effects such as the temporal perception of ambiguous figures, autostereograms, and moving patterns are presented and interpreted from the perspective of nonlinear dynamics. Furthermore new results on the interdependency between the perception of colour and motion are presented, including an explanation of the classic "Fluttering Hearts effect" and the new "Leaning Tower of Pisa effect" which is responsible for a perceptual shift of rotating coloured areas.

Fechner-Benham subjective color is widely believed to be governed by local interactions in early (probably retinal) mechanisms. Here we report three lines of phenomenological evidence that suggest otherwise: subjective colors seen in spatially extended stimuli (a) are dependent on global aspects of the stimuli; (b) can become multistable in position; and (c) even after being stabilized do not support the creation of McCollough's colored after-effects--a cortically based phenomenon generally thought to be more central than Fechner-Benham color. These phenomena suggest a central locus that controls perception of subjective color, characterized by pattern dependent interactions among cortical mechanisms that draw their inputs from peripheral units.

Autostereograms can be perceived in different well-defined spatial levels. Therefore they are an excellent tool with which to examine spatiotemporal processes of multistable three-dimensional perception. We study properties of spatial ambiguity such as phase transitions between different spatial levels and hysteresis in perception with and without noise. We show that the perception of physical noise-which is added to the autostereograms in the form of a random dot pattern-is dependent on the perceived spatial level. We demonstrate that noise can be helpful for the perception of depth in some cases. We show that the signal-to-noise ratio of depth perception is enhanced at an intermediate level of noise strength that is the signature of stochastic resonance in depth perception.