Watercolor illusion

The watercolor illusion, also referred to as the water-color effect, is an optical illusion in which a white area takes on a pale tint of a thin, bright, intensely colored polygon surrounding it if the coloured polygon is itself surrounded by a thin, darker border (Figures 1 and 2).

[3] The watercolor illusion is best when the inner and outer contours have chromaticities in opposite directions in color space.

[1] Pinna, Gavin Brelstaff, and Lothar Spillmann [de] published the first account of the phenomenon in English in 2001, giving it its current name.

There are seven Gestalt factors that the Watercolor Illusion filling of the figure-ground organization were compared to: proximity, good continuation, closure, symmetry, convexity, amodal completion, and past experience.

The first experiment tested the watercolor effect versus proximity to determine the figure-ground segregation.

In some cases, the figure-ground areas were reversed as the filling-in of the orange flank was stronger than the filling in of the purple.

With different variations of a square-wave pattern and basic contours with fringes, the good continuation of the stimuli was studied.

Parallel wavy lines (rivers) were spaced apart with the purple contours on the inside and orange on the outside.

The concave regions were typically perceived as figure whether the purple was flanked by red or orange fringes.

Amodal completion is not a classical principle of figure-ground segregation that helps explain the perception of an object’s hidden regions.

From the experiments, amodal completion does not hold true when the watercolor illusion reversed the perceived segregation of components.

The seventh experiment was to determine if the observer would see the color spread effect if the stimulus was of a common object.

The stimuli were presented 50 cm away from the observer with no time limit on determining the color spread.

It was determined that the color spreading reported from the experiment decreased with increasing length of the shorter axis.

The smallest interval for the electromagnetic shutter was 100 ms, and the continuous color could be seen at the time duration.

The color spreading was perceived the strongest when the contour and fringe subtended a visual angle of 6 arcminutes; The strength of the illusion was discovered to decrease as the thickness of lines increased.

The effects are the strongest with the wave patterns, however, the watercolor illusion is still strong for a stimulus with straight borders.

The colors were drawn with magic marker with pairs of red, green, blue, and yellow lines.

The sixth experiment tested the contrast between the different color lines to see which produced the most striking effect.

For lighting conditions, the color spreading effect declines as the illumination in the room increases.

All of the main properties can be seen with any pair of complementary (opposite in color space) contour lines.

[12] This can be difficult in determining if the boundaries of the hole belong to the background or the watercolor region because it appears that both options can be true.

The parallel boundary processing stage organizes the geometrical structure of the stimulus into the color spreading of the watercolor illusion.

However, the neural mechanisms are more complex as reducing the geometric structure of the stimulus changes the appearance and strength of the watercolor illusion.

The LAMINART model betters explains spatial competition which occurs when the boundary is weakened (e.g. dotted line).

Figure 1. A figure similar to that of Figure 1 of Broerse, Vladusich, and O’Shea (1999), [ 1 ] demonstrating what became known as the watercolor illusion. The vertical gratings are black and white with a thin line of red along each black bar. The horizontal gratings are black and white with a thin line of green along each black bar. The illusion is that the red and green appear to spread over the black and white regions of the vertical and horizontal gratings respectively.
Figure 2. Figure 1 from Pinna (2008). [ 2 ] Purple undulated contours adjacent to orange ones are perceived as a map of the Mediterranean Sea (picture a) and the Gulf of Mexico (picture b) evenly colored by a light veil of orange tint spreading from the orange contours (coloration effect). The two shapes show a strong figure-ground segregation and a solid figural appearance comparable to a bas-relief illuminated from the top and to rounded surfaces segregated in depth and extending out from the flat surface (figural effect). On the contrary, the complementary regions appear as empty spaces with the appearance of holes.
The blue and yellow border gives the illusion that the Afro-Eurasian map is filled in pale yellow though it is actually white