Eye movements in the visual search of word lists.

The word identification span refers to the area of the visual field in which words can be identified during a single fixation. The purpose of the study was to estimate the vertical word identification span in a visual word search task, in which words were arranged in a vertical list. In addition, we studied the effect of list layout (orientation, length, and line spacing) on the speed of search and eye movements. The task of the observer was to identify a target word in a word list, where the other words were distracters. Threshold search time, that is, stimulus presentation time for correct identification at a probability level of 0.79, was determined by using a multiple alternative staircase method. Eye movements were recorded simultaneously. The results showed that, in vertical lists, 4-5 words could be identified during a single fixation. Thus, the vertical word identification span was 4-5 character spaces, whereas according to previous studies the horizontal word identification span is about 10 character spaces, which corresponds to 1-2 words. There were fewer fixations and the saccade amplitudes were smaller for vertical than for horizontal lists of the same length. However, search times did not depend on list orientation. This was due to longer fixation times for vertical lists. Further, since average fixation duration for vertical lists was longer than for horizontal lists, processing time seems to depend on the number of items within the span.