The AMBEGUJAS Phenomenon and Colour Constancy

Abstract

The AMBEGUJAS phenomenon is a reversible flat figure that is spontaneously shifting between two apparent 3-D shapes-'tile' and 'roof'. 2-D perceptions have very rarely been reported. Tied to the shifts between the tile and roof shapes are remarkable changes of perceived colour. In our example, the tile appears to have orange (top half) and blue-green (bottom half) surface colours in white light. The roof appears grey but in an orange illumination and with a blue-green shadow. This phenomenon appears whether a grey display is presented in two coloured illuminations, or a chromatic display with two surface colours (orange and blue-green) is presented in white light. In the coloured illuminations the tile is an example of non-constancy, since its colours are non-veridical colour perceptions. The centre stripe of the display appears to have the same orange and blue-green colours as the lateral stripes but in a shadow. This seems like a colour constancy in a non-constancy situation. An alternative to the classical definition of colour constancy is discussed.

Recognized visual space of illumination: No simultaneous color contrast effect on light source colors

“…Bergström 27 showed an interesting phenomenon called the AMBEGUJAS, which is a reversible flat two-dimensional figure spontaneously shifting between two apparent threedimensional shapes, i.e., "tile" and "roof." It was reported that two-dimensional perception is almost not found.…”

“…The analogy is also found by Bergström et al 28 in the chromatic flat figure under white light condition. Based on a possible invariance hypothesis, 27 when the figure is alternately perceived as the three-dimensional roof, inherent colors of the flat figure seem to be transferred into the illumination, i.e., "the shifts between modes of appearance of colour," 27 causing the desaturated appearance of the figure. It should be emphasized that the term "mode" used by Bergström is implied whether inherent colors in the flat figure are recognized as an attribute of the illumination or the surface.…”

Interactions between luminance and color signals: Effects on shape

“…This was suggested as being due to the visual system's interpretation of chromatic and luminance gradients arising from interreflections. In a related phenomena (AMBEGUJAS, see Bergstrom 2004), perceived color was studied for a folded card stimulus that was bistable: Observers alternated between perceiving pairs of panels as forming roof-shaped convexities or book-shaped concavities. The apparent color and brightness of panels changed when an object's apparent shape flipped from one state to the other.…”

Amodal Completion of Boundaries in Coloured Surfaces

“…This problem may be described as a case of Percept-Percept coupling (Epstein, 1997), or in terms of how one perceptual size influences another-e.g. how perceived distance may influence perceived size (Gruber, 1954), or how perceived illumination may determine the perceived surface colour (Bergström, 2004). In this research it was checked whether particular phenomenal aspects of colour interaction that may be described in terms of contrast do in fact influence the figural organisation determined by amodal completion.…”