Perception and Past Experience 50 Years After Kanizsa's (Im)possible Experiment

Abstract

In the revolutionary year 1968, the Institute of Psychology of the University of Trieste directed by Gaetano Kanizsa published a collective volume to celebrate the 70th birthday of Cesare L. Musatti. Kanizsa devoted the opening article to the empirical refutation of an argument developed by Musatti in Structure and experience in perceptual phenomenology. Musatti held that the debate between rationalist and empiricist theories of perception was not scientific, since a crucial experiment on the role of past experience is—in principle—impossible. Besides rejecting his mentor’s argument on logical grounds, Kanizsa produced a parade of visual effects to demonstrate that in several conditions (involving object formation and camouflage, Petter’s rule, phenomenal transparency, shape recognition, motion organization) actual perception violates expectations based on familiarity with specific objects. The empirical refutation of expectations based on past experience was recurrent in Kanizsa’s subsequent production and represents a lively topic of current perceptual science, though Musatti’s smile is still here.

Keywords: Petter’s rule; depth cues; past experience; perceptual organization; phenomenal transparency; shape recognition; stream/bounce effect.

Figure 1.

The pattern on the left is spontaneously perceived as a capital H with a central symmetric decoration. When this occurs, Max Wertheimer’s initials disappear, because of the dominance of good continuation, closure, and symmetry over past experience. Closure makes the effect even stronger in the pattern on the right. Original demonstrations in Wertheimer (1923/2012).

Figure 2.

At first sight, the pattern in (a) looks like a strange unreadable sequence of symbols, while in (b), where the same elements are added, Italians read a meaningful verbal expression. Reproduced from Kanizsa (1968, Figs. 4 and 8).

Figure 3.

The English version of Figure 2. Reproduced from Kanizsa (1979, Figs. 2.3 and 2.5).

Figure 4.

For an Italian reader, the disappearance of the word nume in (a) is surprising, but could be explained by a perceptual preference for closed symmetric structures overcoming the recognition of overlearned letters. A similar demonstration directed to both Italian and English readers, in which mirroring masks a common self-referring word (me) is shown in (b). (a) reproduces Fig. 5 in Kanizsa (1968).

Figure 5.

Perception of a rounded square partially occluded by textured diamonds masks the objectively present regular octagon. Reproduced from Galli and Zama (1931, Fig. 22).

Figure 6.

The original demonstration in Kanizsa (1968, Fig. 12) was obtained by inserting a transparent page with the red outline of a schematic church (visible in (a)) perfectly aligned with some lines of the unfamiliar textured pattern in (b). When the transparent page was turned, the church disappeared (despite its objective persistence in the stimulus).

Figure 7.

The Arizona whale–kangaroo (AWK) studied by Kihlstrom et al. (2018; reproduced from their Fig. 2). More Australians than Americans report seeing also the kangaroo (besides the whale, which is the most likely perceptual solution).

Figure 8.

The black homogeneous region in (a) is perceptually split into two overlapping rectangles, with a preference for the large horizontal rectangle in front. This depth order can be explained by the tendency to minimize the cost of perceptually instantiating missing contours; i.e., by (AB + CD) < (AC + BD) in (b). Panel (b) redrawn from Kanizsa (1968, Fig. 17).

Figure 9.

Reproduced from Kanizsa (1968, Fig. 18).

Figure 10.

The depth order of intersecting outlines in (a) contradicts past experience: The stick appears to pass behind trousers contours and the arm appears to pass behind the belly contour. As shown in (b), both formulations of Petter’s rule (in terms of contour lengths or region areas) are consistent with the paradoxical perceived stratification of the stick. However, Petter’s rule predicts the stratification of the arm behind the belly contour only following the segmentation in (d), not the one in (c). Reproduced from Kanizsa (1968, Fig. 22).

Figure 11.

In Panel (a), the knife blade appears transparent. Reproduced from Kanizsa (1968, Fig. 24). Panel (b) illustrates the geometry of the relevant intersection between the glass stem and the knife blade. Since [(AB + CD) < (AC + BD)], the “thick in front, thin behind” heuristic predicts that the knife is perceived in front of the glass. Panel (c) shows approximate average luminance values (in arbitrary units) for intersection A, where regions [1,2,3,4] meet. As clarified by arrows in Panel (d) (with arrow direction marking the dark–light contrast) the A intersection is a double-preserving nonreversing X-junction.

Figure 12.

Transparent leaves in front of a bottle. Reproduced from Kanizsa (1968, Fig. 25). Here, geometric and photometric factors are in conflict. The ratio of contour lengths slightly favors the bottle-in-front solution, while luminance relations at relevant X-junctions are like in the knife/glass display (Figure 11), making perception of a transparent bottle inconsistent with physical constraints.

Figure 13.

A compelling Petter effect: The homogeneous black region with critical concavities and aligned contours splits into two intertwined flags. Each of the thin poles is perceived as stratified behind the large rectangular fly of the other flag, according to Petter’s rule.

Figure 14.

Two transparency elaborations of Figure 13. The (a) display contains eight single-reversing X-junctions, supporting the perception of a light gray flag in front of a dark gray flag, against Petter’s rule (formulated in terms of either contour lengths or local region areas). The (b) display contains eight double-preserving nonreversing X-junctions, compatible with either a light or dark flag in front; in this photometrically ambiguous case, the flags appear intertwined, according to the geometric constraint expressed by Petter’s rule and against the weaker preference for seeing in front a layer composed of regions with a minimal luminance difference.

Figure 15.

The upside-down Europe is hard to recognize. Reproduced from Kanizsa (1968, Fig. 27).

Figure 16.

Dust jacket of The Logic of Perception (Rock, 1983). Shape misorientation by 90° counterclockwise makes Europe invisible to most observers, at first sight.

Figure 17.

Panel (a) showing stimuli used by Cate and Behrmann (2010) in their Experiment 2. Stimuli in the horizontal row differ by arm thickness (the task-relevant feature); stimuli in the vertical column differ by oval-circle deformation of the central rounded element (the task-irrelevant feature). Average discrimination RTs are plotted in Panel (b) for pre- and postinsertion blocks. The cost of disregarding the irrelevant feature was higher for 3D convex shapes.

Figure 18.

Panel (a) shows the little man animated by a hidden mechanical device that made his legs and arms to oscillate. Panel (b) illustrates the contrast between the physical oscillations of left (L) and right (R) legs and the perceived motion involving a change of identity of legs (rendered by the two lower spatiotemporal paths). Reproduced with modifications from Kanizsa (1968, Figs. 33b and 36).

Figure 19.

The perception of hopping was maintained also when a disk was attached to one shoe. Observers preferentially perceived the less likely exchange from one shoe to the other. Reproduced from Kanizsa (1968, Fig. 37).