This post is based on a book by Stefan Van Der Stigchel titled “How Attention Works: Finding Your Way in a World Full of Distraction.” In searching for something we try to take advantage of what is available in the environment. Something that is unique about the target that we are searching for can make that target pop-out. For example, if we are looking for something that is red and the environment is full of red objects that target will not pop-out. However, if it is the only red target, or if the majority of the objects in the environment are not red, then its redness will make that target pop-out.
Pop-out searching is also called parallel searching. Reaction time is not affected by the number of distractors (non-red targets) in the scene.

Say you are looking for a particular letter in a scene containing many letters. This is termed serial searching. In contrast to pop-out searching, which is an automatic process, serial searching is a conscious process. The reaction time for a serial search will be a function of the number of non-target objects in the scene. These non-target objects are distractors and search time is an increasing function of the number of distractors.

To determine whether a pop-out draws our attention automatically or not, we need to know what happens when the unique object is a distractor and not a target. Test participants were asked to find the anomalous shape among a group of other shapes. All of the shapes in the experiments are white. Half of the searches contain one unique distractor, which in this case is a gray circle. This distractor has the same shape as the other distractors, but it also has a unique color that distinguished it from all the other shapes on the screen, including that of the target object. We process information related to color faster than information related to shape because color is a stronger builder block than shape. In this case the distractor with the anomalous color is stronger that the object with the unique shape. If the unique distractor is not present, the unique shape of the target object results in a pop-out effect, meaning that the shape is able to grab attention quite easily. But it will take much longer to complete the search when the unique color is also present, even though there is no need to look for it. But we cannot escape its presence, not even when we know in advance which color will be doing the distracting. In fact, we will not be able to ignore the distracting color even if the search is repeated for hours on end. Unique color information is so strong that it will always draw our attention.

Making something suddenly appear is the best way to capture a person’s attention. Nothing activates our attention more strongly than a new object. It makes sense that we have evolved in this way. Objects that appear abruptly can represent possible danger. And the sudden disappearance of an object can also be a good reason for focusing attention on it.

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