Humans must regularly locate task-relevant objects when interacting with the world
around them. Previous research has identified different types of information that the
visual system can use to help locate objects in real-world scenes, including low-level
image features and scene context. However, previous research using object arrays
suggest that there may be another type of information that can guide real-world
search: target knowledge. When a participant knows what a target looks like they
generate and store a visual representation, or template, of it. This template then
facilitates the search process. A complete understanding of real-world search needs
to identify how a target template guides search through scenes.
Three experiments in Chapter 2 confirmed that a target template facilitates realworld
search. By using an eye-tracker target knowledge was found to facilitate both
scanning and verification behaviours during search, but not the search initiation
process. Within the scanning epoch a target template facilitated gaze directing and
shortened fixation durations. These results suggest that target knowledge affects
both the activation map, which selects which regions of the scene to fixate, and the
evaluation process that compares a fixated object to the internal representation of the
target.
With the exact behaviours that a target template facilitates now identified, Chapter 3
investigated the role that target colour played in template-guided search. Colour is
one of the more interesting target features as it has been shown to be preferred by the
visual system over other features when guiding search through object arrays. Two
real-world search experiments in Chapter 3 found that colour information had its
strongest effect on the gaze directing process, suggesting that the visual system
relies heavily on colour information when searching for target-similar regions in the
scene percept. Although colour was found to facilitate the evaluation process too,
both when rejecting a fixated object as a distracter and accepting it as the target, this
behaviour was found to be influenced comparatively less. This suggests that the two
main search behaviours – gaze directing and region evaluation – rely on different sets of template features. The gaze directing process relies heavily on colour
information, but knowledge of other target features will further facilitate the
evaluation process.
Chapter 4 investigated how target knowledge combined with other types of
information to guide search. This is particularly relevant in real-world search where
several sources of guidance information are simultaneously available. A single
experiment investigated how target knowledge and scene context combined to
facilitate search. Both information types were found to facilitate scanning and
verification behaviours. During the scanning epoch both facilitated the eye guidance
and object evaluation processes. When both information sources were available to
the visual system simultaneously, each search behaviour was facilitated additively.
This suggests that the visual system processes target template and scene context
information independently.
Collectively, the results indicate not only the manner in which a target template
facilitates real-world search but also updates our understanding of real-world search
and the visual system. These results can help increase the accuracy of future realworld
search models by specifying the manner in which our visual system utilises
target template information, which target features are predominantly relied upon and
how target knowledge combines with other types of guidance information
