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

Richards, 1988; Treisman, 1985), top-down or high-level cognition to link combinations
of visual features to semantic interpretations or labels (Jackendoff, 1983, 1987;
Treisman, 1986, 1988), and processing involving visual attention or visual routines
that include both data-driven and top-down characteristics, and which serve as an
intermediary between feature detection and object recognition (Cooper & Shepard,
1973a, 1973b; Ullman, 1984; Wright, 1998).
Visual search tasks are frequently used to study visual cognition. In such a task,
a subject is usually presented with a visual display consisting of a number of objects.
In the odd-man-out version of this task, in one half of the trials one of the objects
(the target) is different from all of the other objects (the distracters). In the other
half of the trials, the only objects present are distracters. Subjects have to decide as
quickly and accurately as possible whether a target is present in each display. The
dependent measures in such tasks are 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.
Pioneering work on visual search discovered the so-called pop-out effect: the
time required to detect the presence of a target that is characterized by one of a
small number of unique features (e.g., colour, orientation, contrast, motion) is
largely independent of the number of distractor elements in a display, producing
a search latency function that is essentially flat (Treisman & Gelade, 1980). This is
because, regardless of the number of elements in the display, when the target is
present it seems to pop out of the display, bringing itself immediately to attention.
Notice how the target pops out of the display illustrated in Figure 3-11.
Figure 3-11. Unique features pop out of displays, regardless of display size.
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. Figure 3-12 illustrates visual search in objects that
are either connected or unconnected (Dawson & Thibodeau, 1998); connectedness
Elements of Classical Cognitive Science 101