Mind, Body, World- Foundations of Cognitive Science, 2013a

Cognitive penetrability provides a paradigm for testing whether a function of
interest is part of the architecture or not. First, some function is measured as part of
a pre-test. For example, consider Figure 3-13, which presents the Müller-Lyer illusion,
which was discovered in 1889 (Gregory, 1978). In a pre-test, it would be determined
whether you experience this illusion. Some measurement would be made
to determine whether you judge the horizontal line segment of the top arrow to be
longer than the horizontal line segment of the bottom arrow.
Second, a strong manipulation of a belief related to the function that produces
the Müller-Lyer illusion would be performed. You, as a subject, might be told that
the two horizontal line segments were equal in length. You might be given a ruler,
and asked to measure the two line segments, in order to convince yourself that your
experience was incorrect and that the two lines were of the same length.
Figure 3-13. The Müller-Lyer illusion.
Third, a post-test would determine whether you still experienced the illusion. Do
the line segments still appear to be of different length, even though you are armed
with the knowledge that this appearance is false? This illusion has had such a long
history because its appearance is not affected by such cognitive content. The mechanism
that is responsible for the Müller-Lyer illusion is cognitively impenetrable.
This paradigm has been applied to some of the standard mental imagery tasks
in order to show that some of the privileged properties of images are cognitively
penetrable and therefore cannot be part of the architecture. For instance, in his 1981
dissertation, Liam Bannon examined the map scanning task for cognitive penetrability
(for methodological details, see Pylyshyn, 1981a). Bannon reasoned that the
instructions given to subjects in the standard map scanning study (Kosslyn, Ball,
& Reiser, 1978) instilled a belief that image scanning was like scanning a picture.
Bannon was able to replicate the Kosslyn, Ball, & Reiser results in one condition.
However, in other conditions the instructions were changed so that the images had
to be scanned to answer a question, but no beliefs about scanning were instilled. In
one study, Bannon had subjects shift attention from the first map location to the
second (named) location, and then judge the compass direction from the second
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