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

elationships between individuated objects or their parts. As a result, what early
vision “does not do is identify the things we are looking at, in the sense of relating
them to things we have seen before, the contents of our memory. And it does not
make judgments about how things really are” (Pylyshyn, 2003b, p. 51).
Thus it appears that a pure, bottom-up natural computation theory of vision will
not suffice. Similarly, it was argued earlier that a pure, top-down cognitive theory
of vision is also insufficient. A complete theory of vision requires co-operative interactions
between both data-driven and top-down processes. As philosopher Jerry
Fodor (1985, p. 2) has noted, “perception is smart like cognition in that it is typically
inferential, it is nevertheless dumb like reflexes in that it is typically encapsulated.”
This leads to what Pylyshyn calls the independence hypothesis: the proposal that
some visual processing must be independent of cognition. However, because we are
consciously aware of visual information, a corollary of the independence hypothesis
is that there must be some interface between visual processing that is not cognitive
and visual processing that is.
This interface is called visual cognition (Enns, 2004; Humphreys & Bruce, 1989;
Jacob & Jeannerod, 2003; Ullman, 2000), because it involves visual attention
(Wright, 1998). Theories in visual cognition about both object identification
(Treisman, 1988; Ullman, 2000) and the interpretation of motion (Wright &
Dawson, 1994) typically describe three stages of processing: the precognitive delivery
of visual information, the attentional analysis of this visual information, and the
linking of the results of these analyses to general knowledge of the world.
One example theory in visual cognition is called feature integration theory
(Treisman, 1986, 1988; Treisman & Gelade, 1980). Feature integration theory arose
from two basic experimental findings. The first concerned search latency functions,
which represent the time required to detect the presence or absence of a target as a
function of the total number of display elements in a visual search task. Pioneering
work on visual search discovered the so-called “pop-out effect”: for some targets,
the search latency function is essentially flat. This indicated that the time to find
a target is independent of the number of distractor elements in the display. This
result was found for targets defined by a unique visual feature (e.g., colour, contrast,
orientation, movement), which seemed to pop out of a display, automatically drawing
attention to the target (Treisman & Gelade, 1980). In contrast, the time to detect
a target defined by a unique combination of features generally increases with the
number of distractor items, producing search latency functions with positive slopes.
The second experimental finding that led to feature integration theory was the
discovery of illusory conjunctions (Treisman & Schmidt, 1982). Illusory conjunctions
occur when features are mistakenly combined. For instance, subjects might
be presented a red triangle and a green circle in a visual display but experience an
illusory conjunction: a green triangle and a red circle.
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