A Breadth-First Survey of Eye Tracking Applications <s> Psychology <s> Skilled readers read passages that were displayed on a Cathode Ray Tube controlled by a computer. The readers' eye movements were monitored and certain critical words were changed by the computer as the eye was in motion. The experimental technique utilized in the study provided data on how wide the area is from which a reader acquires information during a fixation in silent reading. The results also delineate different types of visual information that are acquired from various areas within the perceptual span. It was found that a reader was able to make a semantic interpretation of a word that began 1–6 character spaces from his fixation point. When he fixated 7–12 character spaces prior to a word, he was able to pick up such gross visual characteristics as word shape and initial and final letters. It was concluded that the skilled reader is able to take advantage of information in the periphery. However, the size of the area from which he does is rather small. <s> BIB001 </s> A Breadth-First Survey of Eye Tracking Applications <s> Psychology <s> Presents an up-to-date overview of data on the relationship between eye movements and visual cognition, particularly in relation to scene perception and reading. Five sections discuss programming saccades, visual search/integration, scene perception, reading and reading and pictures. <s> BIB002 </s> A Breadth-First Survey of Eye Tracking Applications <s> Psychology <s> The authors present several versions of a general model, titled the E-Z Reader model, of eye movement control in reading. The major goal of the modeling is to relate cognitive processing (specifically aspects of lexical access) to eye movements in reading. The earliest and simplest versions of the model (E-Z Readers 1 and 2) merely attempt to explain the total time spent on a word before moving forward (the gaze duration) and the probability of fixating a word; later versions (E-Z Readers 3-5) also attempt to explain the durations of individual fixations on individual words and the number of fixations on individual words. The final version (E-Z Reader 5) appears to be psychologically plausible and gives a good account of many phenomena in reading. It is also a good tool for analyzing eye movement data in reading. Limitations of the model and directions for future research are also discussed. In his seminal book, The Psychology and Pedagogy of Reading, Huey (1908) wrote that to completely analyze what we do when we read would almost be the acme of a psychologist's achievements, for it would be to describe very many of the most intricate workings of the human mind, as well as to unravel the tangled story of the most remarkable specific performance that civilization has learned in all its history. (p. 6) The goal of this article, therefore, is not to explain reading. Instead, our aims are more modest; we hope to give a reasonable account of how cognitive and lexical processing influences the eye movements of skilled readers. We believe, however, that this is an important and necessary enterprise for several reasons. <s> BIB003 </s> A Breadth-First Survey of Eye Tracking Applications <s> Psychology <s> The span of the effective stimulus during visual search through an unstructured alphanumeric array was investigated by using eye-contingent-display changes while the subjects searched for a target letter. In one condition, a window exposing the search array moved in synchrony with the subjects’ eye movements, and the size of the window was varied. Performance reached asymptotic levels when the window was 5°. In another condition, a foveal mask moved in synchrony with each eye movement, and the size of the mask was varied. The foveal mask conditions were much more detrimental to search behavior than the window conditions, indicating the importance of foveal vision during search. The size of the array also influenced performance, but performance reached asymptote for all array sizes tested at the same window size, and the effect of the foveal mask was the same for all array sizes. The results indicate that both acuity and difficulty of the search task influenced the span of the effective stimulus during visual search. <s> BIB004
Perhaps the first well-known use of eye trackers in the study of human (overt) visual attention were those conducted during reading experiments. BIB002  provides an excellent survey of eye tracking applications in reading and other information processing tasks. Reading  synthesizes over 100 years of research. While the reader is referred to Rayner's article for the complete review, three interesting examples of eye movement characteristics during reading are summarized here. First, when reading English, eye fixations last about 200-250 ms and the mean saccade size is 7-9 letter spaces. Second, eye movements are influenced by textual and typographical variables, e.g., as text becomes conceptually more difficult, fixation duration increases and saccade length decreases. Factors such as the quality of print, line length, and letter spacing influence eye movements. Third, eye movements differ somewhat when reading silently from reading aloud: mean fixation durations are longer when reading aloud or while listening to a voice reading the same text than in silent reading. There is of course a good deal more that has been learned (e.g., BIB003 summarize some basic data on reading and eye movements related to their subsequent effort on modeling of the reading process), here, the methodology behind such discoveries is what is of primary interest. In addition to descriptive studies, where eye movements are simply recorded during reading of text, eye trackers have been used to modulate the stimulus display in real-time depending on where the reader is looking. Three experimental paradigms, the moving window, boundary, and foveal mask, have been developed to explore eye movements (see BIB003 for a concise review and examples of these techniques). Although first developed for reading studies, these paradigms have since been adapted to other contexts such as scene perception (see below). In the moving window paradigm, or gaze-contingent display change paradigm, developed by McConkie and Rayner (1975) , a window is sized to include a number of characters (e.g., 14) to the left and right of a fixated word. The assumption with this technique is that when the window is as large as the region from which the reader can obtain information, there will be no difference between reading in that situation and when there is no window. Conversely, a foveal mask, developed by Rayner and Bertera (1979) (see also BIB004 ), is placed over a number of fixated characters (e.g., 7), creating an artificial foveal scotoma. Eye movement behavior in this situation is quite similar to the eye movement behavior of patients with real scotomas  . In the boundary technique, developed by BIB001 to investigate the use of peripheral information in reading, the stimulus changes as fixation crosses a predefined boundary. In this technique, a word or nonword letter string is initially presented in a target location. When the reader's gaze moves to that location, the initially presented stimulus is replaced by the target word. The fixation duration on the target allows the experimenter to make inferences about the type of information acquired from the target location when it was in parafoveal vision. The motivation behind BIB001  use of eye movements for the study of reading was due in part to his having found tachistoscopic methods to be inadequate. Tachistoscopic (strobe-like) presentation of letters and words relies on the presentation of material for very brief exposures to exclude the possibility of an eye movement during the presentation. Prior to eye tracked reading studies, the tachistoscopic exposure was often thought of as being analogous to a single fixation during reading. Rayner argued that what subjects report from a tachistoscopic presentation cannot be taken as a complete specification of what they saw. The argument for eye movement recording over tachistoscopic displays carries over to scene perception and is discussed in greater detail in the next section.