Experiment in the style of A. Treisman (1980s to present).
Search for a particular target item among an array of distractor items.
Stimuli and Procedure:
- For this example, the items vary on two attributes: shape (square
vs. circle) and color (black vs. white). The participant is told in
advance what item she or he is searching for. In this example, the
participant is told to look for a white circle. This is a
case of conjunction search, because the target is defined by
the conjunction of white with circular. Participants are told to
respond as quickly as possible by pressing either the
target-present key or the target-absent key.
Independent (Manipulated) Variables:
- (1) The target could be present or absent. (2) The number of
items in the array can be few or many. An example of four possible
displays appears below:
|Conjunction Search: Look for a White Circle.|
|Few Items||Many Items|
Dependent (Measured) Variable:
Response time (RT).
Typical results show a linear increase in response time as the
number of items increases. Moreover, the slope of the line (i.e.,
the rate of increase) for target-absent trials in two times
the slope of the target-present trials.
- These results can be accounted for by a process called serial
self-terminating search. A flow chart for this process is shown below:
Flow chart for serial exhaustive search.
The linear increase in RT is explained by the fact that for every
item added to the display, the process must go through the loop that
checks whether the item is the target. The double slope for
target-absent items is explained by the fact that all the
items must be checked when there is no target to be found, but if
there is a target present, then on average only half the
items must be checked until the target if found.
This theory emphasizes processing, and does not make strong
commitments about representation. It assumes that items are
represented in such a way that they can be separately attended to;
i.e., the format is in fact as separate items. But beyond that, the
theory doesn't specify whether the items are represented as templates
or features or structures or whatever.
This experiment and theory
provide a good example of the knowledge organization emphasized in the
syllabus. See if you can fill in all the relevant information in the
diagram at left.
Copyright © 2000 by John K. Kruschke