Summary: Contrasting theories of White's illusion
Howe (2001) presents a new variant of White's illusion and asserts that it demonstrates
the failures of a number of models of White's illusion, including my own (Anderson
1997). He also argues that the FACADE model of Grossberg can explain this effect,
as well as the other published variants of White's illusion (Grossberg 1997; Kelly and
Grossberg 2000). My response has two parts. First, although Howe's display does reveal
the need to go beyond the local properties of T-junctions, I contend that it does not
provide a critical test of the two competing explanations of White's effect (namely, a
contrast theory, and a scission theory). Second, I will argue that although the FACADE
model can provide some insight into this particular variant of White's illusion,
it actually fails to account for White's original effect or variants of the illusion I have
published previously (Anderson 1997).
Howe's demonstration consists of a very weak version of White's effect containing
a single target bar. The main change to White's stimulus is the addition of extended
black and white horizontal bands that cut across the image. In his display, the con-
tours of these bands are carefully aligned with the stems of the targets' T-junctions.
Howe finds that observers report that the illusion is either greatly reduced or inverted
by this manipulation. He argues that this impacts negatively on T-junction-based theories
of this illusion, since the local T-junctions are unchanged in the top and bottom figure.
This seems fair enough, and points to a need to consider other, nonlocal properties