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

is a property that is not local, but is only defined by relations between multiple features
(Minsky & Papert, 1988). The larger the number of display items, the longer it
takes to find the target when it is present in the display. Is there a target in Figure
3-12? If so, is it harder to find than the one that was present in Figure 3-11?
Figure 3-12. Unique combinations of features do not pop out.
Search latency results as those described above, which revealed that some objects
pop out but others do not, formed the basis for feature integration theory (Treisman,
1985, 1986, 1988; Treisman & Gelade, 1980; Treisman & Gormican, 1988; Treisman,
Sykes, & Gelade, 1977). Feature integration theory is a multistage account of visual
cognition. In the first state, preattentive processors register the locations of a small
set of primitive visual features on independent feature maps. These maps represent
a small number of properties (e.g., orientation, colour, contrast movement)
that also appear to be transduced by early neural visual detectors (Livingstone
& Hubel, 1988). If such a feature is unique to a display, then it will be the only active
location in its feature map. This permits pop out to occur, because the location of
the unique, primitive feature is preattentively available.
Unique combinations of features do not produce unique activity in a single feature
map and therefore cannot pop out. Instead, they require additional processing
in order to be detected. First, attentional resources must be used to bring the
various independent feature maps into register with respect to a master map of
locations. This master map of locations will indicate what combinations of features
coexist at each location in the map. Second, a “spotlight” of attention is used to
scan the master map of locations in search of a unique object. Because this attentional
spotlight can only process a portion of the master map at any given time, and
because it must be scanned from location to location on the master map, it takes
longer for unique combinations of features to be found. Furthermore, the search
of the master map will become longer and longer as more of its locations are filled,
102 Chapter 3