Gestalt Psychology is an attempt to understand how we acquire and maintain meaningful perceptions, in an apparent chaotic world. The central principle of gestalt psychology is that the mind forms a global whole. In art, we are concerned with the principle of perception and the relationship between the constituent parts and the whole of the visual experience. Since the visual world provides us with a never ending constant stream of information, our minds try to make sense of this by finding the simplest solution. Like all things in nature, it finds the path of least resistance.
There are various principles in gestalt theory which apply to art in various ways, such as emergence, reication, multistability, invariance and prägnanz.
The most famous example of this principle is the Necker cube.
The Necker cube is a 2-dimensional representation of a 3-dimensional wire frame cube. The ambiguous nature of the drawing, forces the brain to interpret the ambiguous aspects of the image, to make the whole image more consistent, with what would be possible in the real world. Variations of this idea exist in the impossible cube and the Penrose triangle.
These images while at first glance, appear to be 2 dimensional representations of 3 dimensional objects, closer inspection shows that they could not be constructed in the real world. The same ideas work to a degree, that the brain will select an orientation for the cube, we realise the impossibility of the structures, yet due to our learned experiences of depth perception, we can not help but see the images as being partly 3-Dimensional. During the 1970s a constructivist (indirect) theory of perception which is a 'top-down' theory. This proposes that visual information collected, the brain then attempts to interpret this information using, knowledge and expectations and experiences already stored within the brain, to infer what is being seen. In the case of the Necker cube, one of the faces can be seen to switch between being at the front of the cube or being the back face of the cube, due to our preconceived perceptions of near and far. The images become 'unstable' and break down when the brain is unable to decide between the two possible hypothasis.