Encyclopedia of Color Science and Technology

2016 Edition
| Editors: Ming Ronnier Luo

Perceptual Grouping and Color

Reference work entry
DOI: https://doi.org/10.1007/978-1-4419-8071-7_220

Synonyms

Definition

Perceptual grouping refers to principles by means of which a set of discrete elements are partitioned into groups by the visual system, thus forming higher-order perceptual units. Perceptual grouping was first studied by Max Wertheimer, one of the fathers of Gestalt psychology [1]. It is a core topic within the studies of perceptual organization, along with figure-ground segmentation [2]. As regards to color, one can consider either the role of color in perceptual grouping or the effects of perceptual grouping on the perception of color. In the first case the focus is on how color can aid and affect the perceptual organization of the visual scene. In the second case the focus is on how the color appearance of a given surface is affected by the color of other surfaces with which it is perceptually grouped.

Overview

Perceptual grouping is, along with figure-ground segmentation, a core topic in the studies of perceptual organization, i.e., of those processes that structure the sensory input into coherent units (visual objects, entities, and events), thus contributing significantly to the layout of the visual scene. From such a definition, it is clear that grouping and segmentation are two faces of the same coin, as originally postulated by the fathers of Gestalt psychology Max Wertheimer, Wolfgang Köhler [3], and Kurt Koffka [4].

The main factors that regulate perceptual grouping are the following: proximity, similarity, common fate (similarity in motion or change in time), good continuation, closure, prägnanz (or good gestalt or structural coherence), and past experience. These factors are also known as gestalt “principles” or “laws.” Color comes into play with the factor similarity. Figure 1a shows a regular square lattice of dots, and one can group the dots in many ways to form subpatterns, yet none of such patterns is specific to the lattice. By selectively introducing a color difference between the dots, the visual system can be forced to group the dots into patterns or to form larger units based on color similarity. Figure 1b, for instance, shows a yellow arrow; notice however how the grouping effect weakens if the dots that make the arrow in Fig. 1b show instead multiple colors as in Fig. 1c. Color similarity is a relatively strong factor that can overrun other types of similarities, such as shape (Fig. 1d–e) and size (Fig. 1f). It can also overrule a relevant factor such as proximity (Fig. 1g–h); however, it cannot easily overrun good continuation (Fig. 1i). Finally, while color differences among elements do not seem to affect closure (Fig. 1j left), grouping by color similarity can be employed to mask closure (Fig. 1j right).
Perceptual Grouping and Color, Fig. 1

Grouping by color similarity. (a) Gray dots organized in a regular square lattice within which no other group or visual structure emerges. (b) By selectively introducing a change of color in some of the dots, one can generate specific patterns; (c) notice that the strength of the pattern is directly influenced by the color similarity of the dots: in this lattice 30 % of the dots that form the arrow are made of colors other than yellow, and the impression of an arrow-like structure is weakened. (d) This lattice is made of round and square dots; because of shape similarity, the lattice appears vertically organized in pairs of columns; (e) color similarity can overrun shape similarity, switching the perceptual organization from columns to rows. (f) This pattern would normally appear as dots organized in columns according to the factors size similarity and proximity; by introducing color, another pattern within the pattern appears. (g) Because of proximity, the configuration normally appears organized in horizontal rows (right side); color similarity however overruns the factor proximity forcing a perceptual organization in vertical columns (left side). (h) Number 4 appears in spite of proximity and good continuation; notice however that in this configuration and the one in (f), the red patterns can be seen as if they were under the lattice, an impression that recalls transparency. (i) Color similarity does not disrupt good continuation; instead, it generates a second-order group because of which the intersection between the curvy line and the straight line becomes a salient feature of the configuration. (j) On the left, the factor closure determines the impression of a circle with a red arch; on the right, the red arch is grouped with other red ones, masking the completion effect. Notice however that in this last case, the light blue circle appears to complete amodally under the structure formed by the red arches

As a grouping factor, color similarity is not “all or none” (Fig. 2): this makes color similarity an extremely ductile tool in art, graphic design, cognitive ergonomics, etc., as it can be used to enhance, impose, or create visual structure or to hinder or mask the perception of structure and form, such as in animal mimicry or in military camouflage.
Perceptual Grouping and Color, Fig. 2

Grouping by color similarity is not all or none: in (a), the light green and the dark green dots are grouped separately in substructures that are then combined together to form the impression of a global ray fish-like structure. In (b), dots are of three different shades of green, loosely organized with brighter greens at the center and darker greens in the periphery of the ray fish-like structure. This type of grouping is commonly observed in pictorial art and can be easily appreciated in the art movement known as Pointillism. The case represented in (c) is somewhat similar to the one shown in Fig. 1c; however, here, the ray fish-like structure emerges more easily because of the limited number of colors used and the way they are ordered, with the green dots grouped in the center, the yellow ones surrounding the green dots, and the red dots delimiting the periphery. This kind of grouping can be exploited to show energy patterns (for instance, patterns of neural activation, intensity distributions, etc.)

The Effects of Perceptual Grouping on Color

More problematic is the account of the effects of perceptual grouping on color. In an early paper, Fuchs [5] described situations in which perceptual grouping leads to color assimilation. Though sometimes reported by different authors (see, for instance, [6, 7]), older books dedicated to color perception [8, 9] curiously do not make mention to Fuchs’ findings on color assimilation and grouping. The issue may depend on the fact that Fuchs’ demonstrations do not always work on paper (or screen), maybe because they were mostly created by using light, shadows, projections, and reflections.

An attempt to graphically replicate one of Fuchs displays is made in Fig. 3a, b, in which two identical gray dots are placed one at the center of a square made of four blue dots and the other at the center of a square made of four yellow dots. According to Fuchs, the gray dot surrounded by blue dots should appear bluish, while the gray dot surrounded by yellow ones should appear yellowish. The impression however, though rather weak, seems to go in an opposite direction: that of contrast, at least as far as lightness (achromatic surface color) is concerned. Fig. 3e, f employs proximity and good continuation to create two rows of respectively yellow and blue dots, which both incorporate an identical green dot: for those who will get an assimilation effect, the green dot grouped with the yellow dots will look somewhat more yellowish than the green dot grouped with the blue ones. It is not uncommon, however, to have observers reporting an opposite finding or the same observer reporting switches from assimilation to contrast and vice versa.
Perceptual Grouping and Color, Fig. 3

(ab) A graphic interpretation of one of Fuchs’ displays: the central gray dot should appear bluish when surrounded by blue dots and yellowish when surrounded by yellow dots. (cd) A typical lightness contrast effect due to perceptual grouping and accountable in terms of the anchoring theory for lightness perception [6]. (ef) Two straight lines of dots (proximity, good continuation), one yellow and the other blue, both including a green dot. Similar configurations can give rise to either assimilation or contrast

While the perceptual outcomes emerging from the observation of Fig. 3e, f are not clear, those deriving from Fig. 3a, b recall the effects of perceptual grouping on lightness: a middle gray target that is grouped with dark gray surfaces will look lighter than a middle gray target that is grouped with light gray surfaces (Fig. 3c, d) [10].

Future Directions

Was Fuchs completely wrong when he wrote about color assimilation as an effect of grouping elements into meaningful wholes? As mentioned earlier, his experimental setups were quite different from those commonly used nowadays; hence, before any conclusion can be drawn, his experimental setups need to be replicated. Moreover, Fig. 4 may be considered in support of Fuchs’ claims, who insists on the idea of assimilation as a reduction of differences among the parts grouped to form a gestalten. In Fig. 4 the two configurations made of zebralike structures, derived from a modification of a well-known graphic artwork by Victor Vasarely, show strong effects of color assimilation in which not only the “critical” color (to use Fuchs terminology – in Fig. 4a green stripes, in Fig. 4b red ones) assimilates chromatic qualities of the stripes with which they are grouped but also the blue and yellow stripes pickup characteristics of the critical colors. For instance, in Fig. 4a the yellow stripes have a greenish tinge, while in Fig. 4b they show a slight orange tinge.
Perceptual Grouping and Color, Fig. 4

Colored zebras chromatically modified from one of Vasarely’s graphic artworks. (a) The green stripes appear yellowish on the yellow-striped zebra, while they appear bluish on the blue-striped zebra. (b) The red stripes appear with an orange tinge on the yellow-striped zebra and slightly purplish on the blue-striped zebra. Moreover, the assimilation effect works both ways: the yellow and blue stripes in (a) appear with a green tinge, while the physically identical yellow and blue stripes in (b) appear to be affected by the red stripes

Cross-References

References

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    Wertheimer, M.: Untersuchungen zur Lehre von der Gestalt. II. (Investigations on the theory of shape). Psych Forschung 4, 301–350 (1923)CrossRefGoogle Scholar
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    Palmer, E.S.: Vision Science. Photons to Phenomenology. The MIT Press, Cambridge, MA (1999)Google Scholar
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    Köhler, W.: Gestalt Psychology. Liveright, New York (1929)Google Scholar
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    Koffka, K.: Principles of Gestalt Psychology. Harcourt, Brace and Company, New York (1935)Google Scholar
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    Fuchs, W.: Experimentelle Untersuchungen über die Anderung von Farben unter dem Einfluss von Gestalten (Experimental investigations on the alteration of color under the influence of Gestalten). Zeitschrift für Psychologie 92, 249–325.Google Scholar
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    Metzger, W.: Gesetze des sheens (The laws of seeing). Verlag Waldermar Kramer, Frankfurt am Main (1975)Google Scholar
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    Van Lier, R., Wagemans, J.: Perceptual grouping measured by color assimilation: regularity versus proximity. Acta Psychol. 97, 37–70 (1997)CrossRefGoogle Scholar
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    Katz, D.: The World of Colour. Kegan Paul, Trench, Trubner, London (1935)Google Scholar
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Copyright information

© Springer Science+Business Media New York 2016

Authors and Affiliations

  1. 1.Department of PsychologyUniversity of Milano-BicoccaMilanItaly
  2. 2.Department of NeuroscienceUniversity of ParmaParmaItaly