It is generally assumed that the visual system represents stimulus features veridically to enable us to get around in the visual world. This is called naïve realism. However, the physical stimulus cannot always explain the phenomenology of what we see. Just think of visual illusions. Here we see what is not there. Also, many stimuli are ambiguous and yet we see only one percept. The fact that percepts cannot be fully accounted for by knowledge of the stimulus is called the inverse optics problem. Nevertheless, we see sufficiently well in order to navigate, find food, find mates, and escape danger.
The Gestaltists were well aware of these achievements and assigned visual perception an active role in parsing the visual input. Their approach is best captured by Koffka’s question: Why do we see the way we do and not differently? Furthermore: What is it that phenomenology is trying to tell us? Can we deduce the structural factors that govern figure-ground organization and grouping from simple observations?
Numerous examples suggest that our perception is structured by inherent “laws” that are responsible for the way in which scenes are segmented, figures are segregated on the ground, and stimuli are grouped. These laws of seeing (Metzger) are the so-called Gestalt factors of closure, smooth continuation, proximity, symmetry, and similarity under the overarching principle of good Gestalt or Praegnanz. The strongest factor is the factor of common fate that governs grouping in moving stimuli. All these factors were shown to be effective both in adults and children, although to different extents, and also in many species of animals. They are assumed to be largely innate and are considered laws of nature.
While the Gestalt factors enable us to see, they are equally suited for hiding, for example, in camouflage. Powerful measures for hiding an object from perception are: tearing up the uniformity of its surfaces, wrongly partitioning surfaces, and breaking up the borders through inappropriate continuations. The universality of the Gestalt laws in man and nonhuman species implies that the visual brains of such species are similar to ours. Today’s neuroscience aims at finding neuronal correlates and mechanisms for the descriptive categories of the Gestaltists. The talk will discuss the emergent role of such mechanisms for the perception of border ownership, completion of real and illusory contours, and grouping of coherently moving patterns.
Literature
Spillmann, L. and Ehrenstein, W.: Gestalt factors in the visual neurosciences. In: Chalupa, L. and Werner, J.S. (Eds.): The Visual Neurosciences (pp. 1573-1589). MIT-Press, Cambridge, MA 2004