Gestalt Principles of Perception

Before the brain can recognise anything, it has to solve a quieter problem: which parts of the incoming image belong together. A scene arrives at the eye as a jumble of edges, colours and boundaries with no labels attached. Something has to group these patches into one object and those into another before recognition can start. The Gestalt psychologists, working in Germany and Austria in the early twentieth century, were the first to set out the rules the brain uses to do it (Wagemans et al., 2012).

Spacing: tighter rows ↔ tighter columns

Colour alternate columns

The Gestalt movement

Gestalt psychology began around 1912 with Max Wertheimer and his colleagues Kurt Koffka and Wolfgang Köhler. Their central claim, summed up in Koffka's phrase "the whole is other than the sum of its parts", challenged the view that perception is assembled piece by piece from separate sensations (Koffka, 1935). Wertheimer's starting point was apparent motion: two lights flashed alternately look like a single light moving back and forth, a movement that isn't in either flash (Wertheimer, 1912). He concluded that the brain perceives organised wholes directly, following built-in tendencies, which became known as the Gestalt principles of grouping (Wertheimer, 1923).

The main principles

Proximity. Things close together are seen as a group, even if they're otherwise identical. The demo's grid of dots falls into rows or columns depending on which spacing is tighter.

Similarity. Things that share features such as colour, shape, size or orientation are grouped, even if they aren't close. Colour alternate columns in the demo and the grid splits into columns, even when the spacing favours rows.

Closure. The brain completes shapes whose outlines have gaps. Give it most of a circle and it sees a circle. Taken further, this produces illusory contours like the Kanizsa triangle, a bright triangle with edges that are never drawn.

Good continuation. Lines are seen as following the smoothest path. Where two lines cross, you see two continuous lines passing through each other, not four segments meeting at a point.

Common fate. Things that move together are grouped together. A flock of birds turning at once is seen as one shape, and a camouflaged animal often gives itself away the moment it moves.

Figure and ground. Most basic of all, the brain has to decide which part of a scene is the object (the figure, seen in front) and which is background (the ground, continuing behind it). Usually that's instant. When two regions are equally good candidates, the decision becomes unstable, which is the mechanism behind Rubin's vase, whose demo lets you tip the balance by changing which region is smaller.

When the principles disagree

In everyday scenes the grouping principles usually agree and quietly deliver one obvious interpretation, so you never notice them. Illusions appear when an image is built so that the cues conflict, or support two organisations equally well. Unable to hold both, perception switches between them. The Necker cube has no shading or overlap to settle which face is in front, so perception settles on one cube, holds it, then flips. Rubin's vase does the same with figure and ground, and animal camouflage works by turning the principles against the viewer, with markings that break an animal's outline into pieces that don't group together.

Everyday design

The Gestalt principles aren't just for textbooks. Designers rely on them to make interfaces readable: spacing groups related controls, shared colours mark items of the same kind, and a box around some text says it belongs together. Typographers use them to group words into lines and lines into paragraphs. Illusions make the rules visible by arranging for them to disagree. For how this grouping fits into the visual system as a whole, see how the brain processes visual information; for the brain regions involved, see the role of the visual cortex.

Sources and further reading

1. Wertheimer, M. (1912). Experimentelle Studien über das Sehen von Bewegung. Zeitschrift für Psychologie, 61, 161–265. Find this reference on Google Scholar
2. Wertheimer, M. (1923). Untersuchungen zur Lehre von der Gestalt II. Psychologische Forschung, 4, 301–350. Find this reference on Google Scholar
3. Koffka, K. (1935). Principles of Gestalt Psychology. Harcourt, Brace. Find this reference on Google Scholar
4. Wagemans, J., et al. (2012). A century of Gestalt psychology in visual perception: I. Perceptual grouping and figure–ground organization. Psychological Bulletin, 138(6), 1172–1217. Find this reference on Google Scholar