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

are instructed to scan across the image to it, pressing a button when they arrive
at the second location.
In the map-scanning version of the image-scanning task, the dependent variable
was the amount of time from the naming of the second location to a subject’s
button press, and the independent variable was the distance on the map between
the first and second locations. The key finding was that there was nearly a perfectly
linear relationship between latency and distance (Kosslyn Ball, & Reisler, 1978): an
increased distance led to an increased response latency, suggesting that the image
had spatial extent, and that it was scanned at a constant rate.
The scanning experiments support the claim that portions of images depict corresponding
portions of the represented objects, and that the spatial relations between
portions of the image index the spatial relations between the corresponding portions
of the imaged objects. (Kosslyn, 1980, p. 51)
The relative complexity evidence obtained from tasks like mental rotation and image
scanning provided the basis for a prominent account of mental imagery known as
the depictive theory (Kosslyn, 1980, 1994; Kosslyn, Thompson, & Ganis, 2006). This
theory is based on the claim that mental images are not merely internal representations
that describe visuospatial information (as would be the case with words or
with logical propositions), but instead depict this information because the format of
an image is quasi-pictorial. That is, while a mental image is not claimed to literally
be a picture in the head, it nevertheless represents content by resemblance.
There is a correspondence between parts and spatial relations of the representation
and those of the object; this structural mapping, which confers a type of resemblance,
underlies the way images convey specific content. In this respect images are
like pictures. Unlike words and symbols, depictions are not arbitrarily paired with
what they represent. (Kosslyn, Thompson, & Ganis, 2006, p. 44)
The depictive theory specifies primitive properties of mental images, which have
sometimes been called privileged properties (Kosslyn, 1980). What are these primitives?
One is that images occur in a spatial medium that is functionally equivalent
to a coordinate space. A second is that images are patterns that are produced by
activating local regions of this space to produce an “abstract spatial isomorphism”
(Kosslyn, 1980, p. 33) between the image and what it represents. This isomorphism
is a correspondence between an image and a represented object in terms of their
parts as well as spatial relations amongst these parts. A third is that images not only
depict spatial extent, they also depict properties of visible surfaces such as colour
and texture.
These privileged properties are characteristic of the format mental images—the
structure of images as symbolic expressions. When such a structure is paired with
particular primitive processes, certain types of questions are easily answered. These
108 Chapter 3