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

esults by demonstrating that they are cognitively penetrable (Pylyshyn, 2003c): a
change in tacit information eliminates the linear relationship between time and
image transformation, which would not be possible if the depictive properties of
mental images were primitive.
If a process such as image scanning is cognitively penetrable, then this means
that subjects have the choice not to take the time to scan attention across the
image. But this raises a further question: “Why should people persist on using this
method when scanning entirely in their imagination where the laws of physics
and the principles of spatial scanning do not apply (since there is no real space)?”
(Pylyshyn, 2003b, p. 309). Pylyshyn’s theory of visual cognition provides a possible
answer to this question that is intriguing, because it appeals to a key proposal of the
embodied approach: cognitive scaffolding.
Pylyshyn’s scaffolding approach to mental imagery was inspired by a general
research paradigm that investigated whether visual processing and mental imagery
shared mechanisms. In such studies, subjects superimpose a mental image over
other information that is presented visually, in order to see whether the different
sources of information can interact, for instance by producing a visual illusion
(Bernbaum & Chung, 1981; Finke & Schmidt, 1977; Goryo, Robinson, & Wilson, 1984;
Ohkuma, 1986). This inspired what Pylyshyn (2007) called the index projection
hypothesis. This hypothesis brings Pylyshyn’s theory of visual cognition into contact
with embodied cognitive science, because it invokes cognitive scaffolding via
the visual world.
According to the index projection hypothesis, mental images are scaffolded by
visual indices that are assigned to real world (i.e., to visually present) entities. For
instance, consider Pylyshyn’s (2003b) application of the index projection hypothesis
to the mental map paradigm used to study image scanning:
If, for example, you imagine the map used to study mental scanning superimposed
over one of the walls in the room you are in, you can use the visual features of
the wall to anchor various objects in the imagined map. In this case, the increase
in time it takes to access information from loci that are further apart is easily
explained since the ‘images,’ or, more neutrally, ‘thoughts’ of these objects are actually
located further apart. (Pylyshyn, 2003b, p. 376, p. 374)
In other words, the spatial properties revealed in mental scanning studies are not
due to mental images per se, but instead arise from “the real spatial nature of the
sensory world onto which they are ‘projected’” (p. 374).
If the index projection hypothesis is valid, then how does it account for mental
scanning results when no external world is visible? Pylyshyn argued that in such conditions,
the linear relationship between distance on an image and the time to scan it
may not exist. For instance, evidence indicates that when no external information is
visible, smooth attentional scanning may not be possible (Pylyshyn & Cohen, 1999).
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