N ico O rlandi Motion is a structured whole or ‘Gestalten’ with its own ontological status and phenomenology Wertheimer extended this theory to the perception of shape and rhythm His model was then developed by his colleagues in Berlin, Wolfang Köhler and Kurt Koffka (Koffka 1935; Köhler 1920) According to Gestalt theory, a perceptual scene has properties that the parts – even when considered together – not have Gestaltists were interested not in how the parts compose a whole, but rather in how the structure of a whole affects its subparts They contrasted structural atomism, with holism This holistic thesis had an effect in philosophy, prompting some theorists to question whether appearances are simple and unadulterated in the way in which sense-data theory and structuralism thought they were (Hanson 1958) According to holism, no appearance is what it is independently of how it is situated in a whole The way an item looks is affected by the way other items in the perceptual field look Thus Gestalt psychology influenced views that questioned the neutrality of perception, a topic on which we will return in the next section (2.2) Gestalt theorists took themselves to be discovering principles of perceptual organization that are not acquired through experience, or association, and that organize whole appearances Although Gestaltists were primarily concerned with rejecting the atomistic convictions of structuralism, they also held views about the physiology of perceiving Köhler proposed two related ideas One was that the brain was a dynamic, physical system that converged towards an equilibrium of minimum energy This idea predates contemporary accounts of the brain based on dynamics and predictive coding (Clark 2013) A second proposal was that the causal mechanism underlying perception was given by a ‘physical Gestalt’ or an electromagnetic field generated by events in neurons.12 Some of these ideas were later shown to be problematic The notion of a physical Gestalt, for example, was in trouble when it was found that disrupting electrical brain fields did not seriously affect perceptual abilities (Lashley et al 1951) These physiological findings may have contributed to Gestalt psychology losing its appeal in the second half of the 20th century The development of computer science, of cognitive science and of neuroscience may also have offered better theoretical frameworks Work on perceptual principles of organization and on the emergent structure of perceptual experience, however, continues to this day (Wagemans et al 2012) 2.2 Constructivism Another powerful idea that shaped work on perception in the 20th century is the constructivist view that perception involves a type of unconscious inference Constructivists stress that sensory stimulation is inadequate in perception In the case of vision, what is projected on the retina consists of light intensities that can be caused by a number of environmental elements How we get to see an object when all that is projected on the retina is light? 114