This is a guest post by Daniel Griffin, one of Greta’s top student writers from Spring of 2007.
Does anything seem stick out about this sentence? I’m sure that if I told you to keep looking for yellow highlighted words, you would not have much trouble finding them in these first few sentences. You could even make it simpler for yourself and just look for any highlighted word. The only highlighted portions are yellow, so what is the difference? Let’s say that by now you are used to searching for these highlighted words by just looking for a different color background than just the usual white. Does it take any longer to find the yellow word in this sentence? For most of us the answer to this question would be not especially, but I bet you glanced twice at “find.” If I were to write the rest of this post in this fashion you would have to change your visual searching strategy to not just look for highlighted words, but yellow words in particular.
This kind of visual searching strategy is called an “attentional set”. More specifically, an attentional set is an innate part of our information processing that prioritizes certain stimuli, such as yellow highlighted words, for selection. So why would we create this set when look for things? Well, using a certain set prevents things other than what we are looking for from distracting us. The problem with creating and using a set is that we do not always use the set that is best for what we are doing. With this in mind, Andrew Leber and Howard Egeth studied our visual searching strategies and the effects of past experience.
Leber and Egeth first defined two major types of attentional sets. The first of which, they define as singleton detection mode. This is a broad way of searching that narrows our attention down to a certain kind of characteristic- i.e. a singleton. The example of the highlighted word in the opening of this blog is a singleton. No matter what color it is, being highlighted makes it a singleton. The second kind of attentional set is called feature search mode. This mode is much narrower way of searching, where we look only for something’s defining feature (i.e. a yellow highlighted word.) There are positives to using both methods. In singleton detection mode, you don’t use as much effort, but it is not as systematic as feature search mode. So how do we decide which one to use? The choice is not entirely ours to make–the presence of a preestablished strategy looks to be the most important factor in which set we use.
To test the importance of a preestablished strategy, Leber and Egeth first divided volunteers in two groups for a “training phase.” The training influenced the groups to use either singleton detection or feature search mode. The general procedure asked subjects to identify a target letter after a rapid presentation of 20 screens with a single, random letter on each and a blank screen in between letters. Each screen was only presented for 50 milliseconds. The group that was influenced to use singleton detection mode searched for any letter that was a different color compared to the other letters. The feature search group looked for a target of a particular color –either red or green. Two screens before the target letter appeared, a number of different distractors might flash — either grey “#” symbols or “#” symbols that were the same or a different color as the target letter. The training phase lasted 30 minutes so that each subject would get used to the influenced set. Here’s an example of the kind of thing viewers experienced. Play this movie (QuickTime required) and see if you can identify the letter that’s displayed in red.
Remember, some viewers were trained to look for specific colors while others were trained to look for any color that was different.
Next, subjects looked for a letter which was either red or green but which color exactly was not announced. These letters were preceded by four types of distractors: no distractors, four grey distractors, three grey distractors and one distractor the same color as the target, and finally three grey distractors and one distractor of a different color than the target.
The results showed a remarkable effect of preestablished strategy. The subjects continued to use the same search method they had used in the training phase. The group that was trained in feature searching still looked for a specific color, which could be shown in the data because there was no difference between the performance on the all grey distractor and different color distractor. Subjects of the singleton search group were seen using the same strategy due to the fact that they performed worse on the same AND different colored distractors. Again, in singleton search mode, you are looking for one characteristic which in this case is the presence of color. The graph below shows the performance of the two groups during the test phase.
Notice the difference between groups when presented with a colored distractor- the feature search group can focus on the task better because they look for a specific color, whereas the singleton search group does not.
In the “test phase,” subjects could use either attentional set. The results show that they did not change which searching style according to the demands of the task. After a reevaluation of how to find the target most effectively, the singleton search group would have adopted more of a feature searching style, but they did not. Conversely, the feature search group may have adopted more of a singleton search style when they looked through screens with only grey distractors, but they did not change approaches either.
Our past experience influences how we search, regardless of which method is most effective. This idea leads to broader questions concerning the basic properties of attentional control. Does the past play a larger part in where we direct our attention than we think? Try spotting the yellow highlighted word this time. Faster?
Leber, A.B. & Egeth, H.E. (2006). Attention on autopilot: Past experience and attentional set. Visual Cognition, 14, 565-583.