findings known asattentional engagement theory. Both of these theories will now
be discussed.
Feature Integration Theory Treisman (1988) drew a distinction between the
features of objects (e.g. colour, size, lines of particular orientation) and the
objects themselves. Her theory based on this distinction includes the following
assumptions:
.There is a rapid initial parallel process in which the visual features of
objects in the environment are processed together; this is not dependent
on attention..There is a second, serial process in which features are combined to form
objects (e.g. a large, red chair)..The second serial process is slower than the initial parallel process, es-
pecially when several stimuli need to be processed..Features can be combined by focused attending to the location of the
object, in which case focused attention provides the ‘‘glue’’ that constructs
unitary objects from the available features..Feature combination can also be influenced by stored knowledge (e.g.
bananas are usually yellow)..In the absence of focused attention or relevant stored knowledge, fea-
tures will be combined from different objects in a random fashion, pro-
ducing what are known as ‘‘illusory conjunctions.’’
Treisman and Gelade (1980) had previously obtained apparently good sup-
port for this feature integration theory using a visual search task. In one of their
experiments, subjects searched for a target in a visual display containing be-
tween 1 and 30 items. The target was either an object (a green letter T), or it
consisted of a single feature (either a blue letter or an S). When the target was a
green letter T, all of the non-targets shared one feature with the target (i.e. they
were either the brown letter T or the green letter X). It was predicted that
focused attention would be needed to detect the former target (because it is
defined by a combination of features), but that the latter target could be detected
in the absence of focal attention because it is defined by a single feature.
The findings were as predicted (see figure 15.6). The number of items in the
visual display had a substantial effect on detection speed when the target was
defined by a combination or conjunction of features (i.e. a green letter T), pre-
sumably because focused attention was required. However, there was practi-
cally no effect of display size when the target was defined by a single feature
(i.e. a blue letter or an S).
According to the feature integration theory, lack of focused attention pro-
duces a state of affairs in which the features of different objects are processed
but remain ‘‘unglued.’’ This should lead to the random combination of features
and illusory conjunctions referred to earlier. This prediction was confirmed by
Treisman and Schmidt (1982). They obtained numerous illusory conjunctions
when attention was widely distributed, but not when the stimuli were pre-
sented to focal attention.
Treisman has modified her feature integration theory in recent years. For ex-
ample, Treisman and Sato (1990) argued that the degree of similarity between
Attention and Performance Limitations 373