Eye movements, search and crowding

Abstract

If you fixate a single letter in a text, you will notice that it is impossible to identify a letter that is only a few letters away. This is caused by letters that flank this target letter. This is an example of the 'crowding' phenomenon, i.e. items that are close enough to each other interfere with each other in perception. In order to identify a crowded object, eye movements need to be made. This thesis is about the relationship between eye movements and crowding. This relationship has mainly been investigated using search tasks. These tasks revealed that on the one side, crowding affects eye movements. When exploring the visual environment, humans automatically adopt a strategy that takes the degree of crowding in the scene into account. With increasing strength of crowding, fixation durations increase and saccade amplitudes become shorter. On the other side, we found that making eye movements affects the perception of a crowded object. We found a surprising advantage: already during the preparation of an eye movement (before fixation of the object!) the perceptibility of a crowded object increases.