This visual illusion (Van Lier,
De Wit, &
Koning, 2006) was also presented at ECVP 2005 (La Coruna, Spain -- it
was selected as one of the best 10 static illusions and was honored
with an exposition in the science musum of La Coruna).
Figures 1 and 2 comprise a grid of grey bars. The
the bars have been ‘obscured’ in different
Figure 1, four three-quarter disks or ‘pacmen’ are
displaced with respect the outer boundaries of the crossing. Such
pacmen configuration are known to induce the perception of an illusory
square (Kanizsa, 1979, Organization in Vision, NY: Praeger). What is
striking is the quite confusing appearance of the display. Observers
may experience a percept in which the crossing of the grey bars is
being watched through “pieces of glass”.
may also experience a displacement of the part of the grid that falls
inside the illusory squares -- as if it has been clipped and shifted.
This volatile percept seems related to the phenomenon in which small
texture-like elements are captured by surrounding illusory contours
(e.g., Ramachandran, 1985, Perception, 14, 127-134), although the
present percept is quite unstable. It may further reflect the visual
system’s attempt to deal with the perceived misalignment by
momentarily (con-)fusing physical and illusory contours. Experiments
confirm the perceived displacements in the pacmen configurations.
In Figure 2, a clear figure ground segregation can be
very different from Figure 1. Here, the pacmen have been replaced by
crosses (at the same positions). As these cross configurations do not
elicit illusory surfaces, the ‘restlessness’ of the
Figure 1. Pacmen configurations are misaligned with an
underlying grid. The percept is quite ‘restless’.
Figure 2. Cross configurations that are misaligned with
an underlying grid. The ‘restlessness’ has now