View source for Eye movements

==Eye movements and visual search==

[[Image:Search.jpg|thumb|left|F4|In this example, the person was told to look for a letter “L” that was reversed.]]

[[Image:Visualsearch.jpg|thumb|right|F5|In this example, the person was told to look for a cactus.]]

Fixation durations in search tend to be highly variable.  Some studies report average fixation times as short as 180 ms while others report averages on the order of 275 ms.  This is undoubtedly due to the fact that the difficulty level of a search (i.e., how dense or cluttered the array is) and the exact nature of the search task will strongly influence how long viewers pause on each item (see  <figref>Search.jpg</figref> and  <figref>Visualsearch.jpg</figref>).  

Typically, saccade size is a bit larger than in reading (though saccades can be quite short with very dense arrays).   

When an array is very cluttered (with many objects and distractors), the search becomes more demanding than when the array is simple.  The eye movements on each of these types of arrays typically reflect this property of an array (Bertera & Rayner, 2000;  Greene & Rayner, 2001a. 2001b).  As the array becomes more complicated, we see an increase in the fixation duration and the number of fixations, as well as a decrease in the average saccade length (Vlaskamp & Hooge, 2006).  

Research has shown that in visual search, the perceptual span varies as a function of the difficulty of the distractor letter. That is, the perceptual span is smaller when distractor items were visually similar to the target than when the distractor items are distinctly different.  

This suggested that there were two qualitatively different regions within the span: a decision region (where information about the presence or absence of a target is available), and a preview region where some item information is available, but where information on the absence of a target is not yet available.

Describing where a person will most likely fixate while performing a visual task is often described using a saliency map (e.g., Guided Search Model, Cave & Wolfe, 1990; Wolfe, 1994, 2001).  The Guided Search model is perhaps the most well known and has sparked a great deal of interest in the guiding mechanisms of visual search.  According to this model, guidance within a search array arises from two sources: bottom-up (prioritizes items according to how much they differ from their neighbors) and top-down (prioritizes items according to how much they share target features).