Illusory Planes in Fred Sandback’s Sculpture

A remarkable feature of artist Fred Sandback’s string constructions has often been noted: that the geometrical forms created with string have a strong planar feel. Phenomenologically, the spaces between the strings are perceived as planes with some substance. The illusion is amodally completed, as in the famous Kanizsa triangle, by minimal prompts, but in three dimensions. Instead of an illusory figure, then, Sandback creates illusory planes. By noting how the constructions are like “impossible” figures, we can see how bottom up and top down effects combine to complicate the illusion and the works become about the construction of space rather than its reification.

Defining the Units of Competition: Influences of Perceptual Organization on Competitive Interactions in Human Visual Cortex

Multiple stimuli that are present simultaneously in the visual field compete for neural representation. At the same time, however, multiple stimuli in cluttered scenes also undergo perceptual organization according to certain rules originally defined by the Gestalt psychologists such as similarity or proximity, thereby segmenting scenes into candidate objects. How can these two seemingly orthogonal neural processes that occur early in the visual processing stream be reconciled? One possibility is that competition occurs among perceptual groups rather than at the level of elements within a group. We probed this idea using fMRI by assessing competitive interactions across visual cortex in displays containing varying degrees of perceptual organization or perceptual grouping (Grp). In strong Grp displays, elements were arranged such that either an illusory figure or a group of collinear elements were present, whereas in weak Grp displays the same elements were arranged randomly. Competitive interactions among stimuli were overcome throughout early visual cortex and V4, when elements were grouped regardless of Grp type. Our findings suggest that context-dependent grouping mechanisms and competitive interactions are linked to provide a bottom–up bias toward candidate objects in cluttered scenes.

Three-part Oppel-Kundt illusory figure

The Oppel-Kundt illusion was examined in the psychophysical experiments with the classical two-part stimuli and modified three-part figures. The modified versions comprised either one filled medial interval and two empty flanking intervals or one empty space situated in between two fillings. The illusion was measured as a function of the number of filling elements in the referential parts of the figures. The curves obtained by two modified figures and by the original two-part stimulus were quite similar in shape, but the magnitudes of the illusions differed significantly. The figure with two filled intervals yielded about twice-stronger illusory effect than the contrasting figure with a single filled and two empty intervals. The two-part stimulus showed the illusion magnitudes in the midst. Our assumption suggests the illusory effect being related particularly to overestimations of the filled interval when compared with the empty interval displayed side-to-side. The unfilled interval might not contribute to the illusion.

Illusory-Contour Figures Prime Matching of Real Shapes

We investigated explicit and implicit properties of the internal representation of illusory-contour figures by studying potential priming effects of this representation. Using a primed matching paradigm (Beller 1971, Journal of Experimental Psychology87 176–182), we found that illusory ‘Kanizsa’ squares and triangles prime later matching of the same shapes, respectively, and not of the alternative shape. This priming effect is present despite the use of an illusory figure as a prime and real shapes as tests. To determine whether implicit processing mechanisms sufficiently induce a representation of the illusory shape so that it can lead to this priming effect, we used a novel method of presentation of the inducing pattern, based on Rock and Linnet's (1993, Perception22 61–76) method for separating (implicit) retinal and (explicit) world-coordinate images. Presence of the implicit retinal image is confirmed by its producing an afterimage. While the retinal image is only implicitly produced by the inducing pattern of pacmen, it is nevertheless available for real-shape match priming. We conclude that Kanizsa-type inducer patterns are processed implicitly until formation of illusory-figure shapes. These are represented at relatively high cortical levels, and shape-matching priming must occur here, too. These results are consistent with the claim of the reverse hierarchy theory that bottom–up processing is generally implicit and that conscious perception originates at high cortical levels.

The Visual Search of an Illusory Figure: A Comparison between 6-Month-Old Infants and Adults

The aim of the present study was to investigate how perceptual binding and selective attention operate during infants' and adults' visual search of an illusory figure. An eye-tracker system was used to test adults and infants in two conditions: illusory and non-illusory (real). In the illusory condition, a Kanizsa triangle was embedded among distractor pacmen which did not generate illusory contours. In the non-illusory condition, a real triangle was included in the same pacmen's display. The results showed that adults detected both the Kanizsa and the real figure automatically and without focal attention (experiment 1). In contrast, 6-month-old infants showed a pop-out effect only for the real figure (experiment 2). The failure of the illusory figure to trigger infants' attention was not due to infants' inability to perceive the illusory figure per se, as infants preferred the illusory figure over a non-illusory control stimulus in a classical preferential-looking task (experiment 3). Overall, these findings indicate that the illusory Kanizsa triangle triggers visual attention in adults, but not in infants, supporting evidence that at 6 months of age the binding processes involved in the perception of a Kanizsa figure do not operate in an adult-like manner.