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

selected—inside makes no sense to compute without their specification. “What the
visual system needs is a way to refer to individual elements qua token individuals”
(Pylyshyn, 2003b, p. 207).
With such considerations in mind, Ullman (1984) developed a theory of visual
routines that shares many of the general features of feature integration theory. In
an initial stage of processing, data-driven processes deliver early representations
of the visual scene. In the second stage, visual cognition executes visual routines
at specified locations in the representations delivered by the first stage of processing.
Visual routines are built from a set of elemental operations and used to establish
spatial relations and shape properties. Candidate elemental operations include
indexing a salient item, spreading activation over a region, and tracing boundaries.
A visual routine is thus a program, assembled out of elemental operations, which is
activated when needed to compute a necessary spatial property. Visual routines are
part of visual cognition because attention is used to select a necessary routine (and
possibly create a new one), and to direct the routine to a specific location of interest.
However, once the routine is activated, it can deliver its spatial judgment without
requiring additional higher-order resources.
In the third stage, the spatial relations computed by visual cognition are linked,
as in feature integration theory, to higher-order cognitive processes. Thus Ullman
(1984) sees visual routines as providing an interface between the representations
created by data-driven visual modules and the content-based, top-down processing
of cognition. Such an interface permits data-driven and theory-driven processes to
be combined, overcoming the limitations that such processes would face on their
own.
Visual routines operate in the middle ground that, unlike the bottom-up creation of
the base representations, is a part of the top-down processing and yet is independent
of object-specific knowledge. Their study therefore has the advantage of going
beyond the base representations while avoiding many of the additional complications
associated with higher level components of the system. (Ullman, 1984, p. 119)
The example theories of visual cognition presented above are hybrid theories in the
sense that they include both bottom-up and top-down processes, and they invoke
attentional mechanisms as a link between the two. In the next section we see that
Pylyshyn’s (2003b, 2007) theory of visual indexing is similar in spirit to these theories
and thus exhibits their hybrid characteristics. However, Pylyshyn’s theory of
visual cognition is hybrid in another important sense: it makes contact with classical,
connectionist, and embodied cognitive science.
Pylyshyn’s theory of visual cognition is classical because one of the main problems
that it attempts to solve is how to identify or re-identify individuated entities.
Classical processing is invoked as a result, because “individuating and reidentifying
in general require the heavy machinery of concepts and descriptions”
382 Chapter 8