| ISLE | Chapter 9
| Experiment: Feature vs. Conjuction Search
One of the most important attentional tasks in vision is visual search In the laboratory, we can control many aspects of visual search. We can control the size, shape, color, and location of the search item as well as the size, shape, color, location, and number of distracting items. We can then measure how long it takes a participant to find the target under these different circumstances. If the item you are searching for is say a different color then everything else, this type of search is quite easy and we call it feature search.
Sometimes, to find the item you are searching for requires you to pay attention to two or more dimensions at a time, say color and shape. These are conjunction searches and are far harder, particularly with a lot of distractors. Sometimes the target only differs in the way it is assembled, say finding a T in a field of L's. This is a very hard search and called a spatial configuration search.
In this experiment you can try each of these types of searches and see how fast you are at finding your target.
To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.
On this tab you can adjust the type of stimulus and the various parameters of the motion of the stimulus to see how this might effect the aftereffect. The settings include the following:
Simulus Size: control the size of the different sitmuli.
Target Color: the color of the target, and in configuration searches, also
some of the distractors. In configuration searches, all stimuli are this color.
Distractor Color: color of the distractors stimuli in feature search
and some of the distractors in conjuction search.
Background Level: brightness of the background .
Reset At the top of the settings page is a Reset button. Pressing this button restores the method settings to their default values.
On this tab you can adjust how the method will work. The settings include the following:
Type of Search: whether a Feature, a Conjuction or Spatial Configuration search.
Number of Trials per condition: how many trials for each level of number of distractors.
Percentage of Trials with Target: the percentage
of trials where the target stimulus is shown.
Number of Levels of Distractors: the number of different distactor conditions.
This number times the number of trials per condition is the total number of trials in the experiment.
Smallest Number of Distractors: the number of distractors in the condition
with the fewest distractors.
Distractor Multipier: each additional condition will be multiplied
by this number to get the number distractors. So with a multplier of 4 and 3 conditions starting
at 4, you will have conditions with 4, 16 and 64 distractors..
Reset At the top of the settings page is a Reset button. Pressing this button restores the stimulus settings to their default values.
On the Experiment tab, press a space button or the button on the screen to start the experiment. On the first trial, the target (on in the configuration trials, 4 targets) will be shown for 1.5 seconds. Targets must be identical in all aspects to that stimulus. Then after a brief pause, the stimuli will be presented and at the bottom of the screen will be Yes and No buttons. If you see the target press the Yes button or the z key. If you do not see the target press the No button or / key. Be fast but accurate in your responding.
You data will presented on this tab. On the x-axis will be the different number of distractor conditions. On the y-axis will be the reaction time responding to the stimuli. Trials when the stimulus is present will be shown as well as when the stimulus is absent. To display the data as values Show Data button.
Change the settings below to alter the stimulus parameters in this experiment.