Sixty-six college students read two chapters from a contemporary novel while their eye movements were monitored. The eye movement data were analyzed to identify factors that influence the location of a reader's initial eye fixation on a word. When the data were partitioned according to the location of the prior fixation (i.e., launch site), the distribution of fixation locations on the word (i.e., landing site distribution) was highly constrained, normal in shape, and not influenced by word length. The locations of initial fixations on words can be accounted for on the basis of five principles of oculomotor control: A word-object has a specific functional target location, a saccadic range error occurs that produces a systematic deviation of landing sites from the functional target location, the saccadic range error is reduced somewhat for saccades that follow longer eye fixations, there exists oculomotor variability that is a second, non-systematic source of error in landing sites, and the oculomotor variability increases with distance of the launch site from the target.

An analysis of over 40,000 eye fixations made by college students during reading indicates that the frequency of immediately refixating a word following an initial eye fixation on it varies with the location of that fixation. The refixation frequency is lowest near the center of the word and positively accelerating with distance from the center. The data are well fit by a parabolic function. Assuming that refixation frequency is related to the frequency of successful word identification, the observed curvilinear relation results naturally from models that postulate a linear decrease in acuity with retinal eccentricity. A single letter difference in fixation location in a word can make a sizeable difference in the likelihood of refixating that word. The effects of word length and cultural frequency on the frequency of refixating are also examined.McConkie, Kerr, Reddix, Zola, & Jacobs EYE MOVEMENT CONTROL DURING READING: II. FREQUENCY OF REFIXATING A WORDDuring reading, people fixate more frequently near the centers of words than near the beginnings and ends (Rayner, 1979). O'Regan (1981) proposed a Convenient Viewing Position hypothesis, stating that readers learn to send their eyes to the centers of words because, across the words in a language, that location is optimal for word identification. Due to the rapid drop in visual acuity with distance from the center of the fovea, together with the fact that letters bounded by spaces are more perceptible (Bouma, 1978;Jacobs, 1987), the letters of a word are maximally identifiable when the eyes are near the word's center. O'Regan further suggested that the further the eyes lie from the Convenient Viewing Position, the greater the probability that a second eye fixation on the word will be required for identification. This prediction was confirmed in a word identification study (O'Regan, 1984), which found that the frequency of making a second fixation on a word is minimized when the initial fixation is near the center of that word. Furthermore, the frequency of refixating increases as the distance of the first fixation from the center of the word increases. We refer to this relationship as the Word Refixation Frequency Curve, or simply as the word refixation curve. The existence of a word refixation curve in word identification tasks has been replicated (O'Regan, Levy-Schoen, Pynte, & Brugaillere, 1984) and there is some evidence that it may also be present in the eye fixation pattern made during reading (Blanchard & McConkie, cited by O'Regan & Levy-Schoen, 1987).

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Prototype low-intensity threat laser eye protection (LIT-LEP) spectacles were evaluated for US Coast Guard (USCG) cockpits and night vision goggle compatibility. The impetus for interest in aviation LIT-LEP is driven in part by the fact that easily accessible 0.5–2.0 W high-power laser pointers exceed safety standards for direct on-axis viewing. A repeated-measures experimental design was used to assess LIT-LEP performance relative to a no-LEP control for the following tasks: Near- and far contrast acuity, night vision goggle far-contrast acuity, emissive and non-emissive light source color-vision screening, and USCG multifunctional display color symbol discrimination reaction time and accuracy. Near- and far-contrast acuity results demonstrated good LIT-LEP performance for typical in- and out-of-cockpit lighting conditions. Night vision goggle performance suffered marginally at only one contrast level (85%; 20/30 acuity line). Color vision test results showed good color balance in that S-, M-, and L-cone performance did not demonstrate a clinical diagnostic color defect for emissive or non-emissive light sources when wearing LIT-LEP. Color symbol discrimination reaction-time-task results based on inverse efficiency scores revealed that some non-primary flight display colors exhibited a combination of slower speed and decreased accuracy. The findings will contribute to an acquisition decision as well as guide future LEP designs.

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The confocal principle was applied to double pass method to measure the point spread function (PSF) of the human eye and an artificial eye, and to improve the ratio of signal to noise of retinal images. The double-pass PSFs of four human eyes on and off the optical axis of the eyes were measured. The off-axis double pass PSF in the human eye along vertical and horizontal direction is asymmetrical. When the subject looks left on the horizontal off axis, the PSF appears right of the optical axis of the subject eye. When the subject looks right the PSF is located left of the optical axis. The location of the PSF on the vertical off axis appears above the optical axis when the subject looks up. When the subject looks down the double pass PSF is located below the axis. The PSFs of the human eye recorded at varying off-axis angles are presented. Asymmetrical results suggest a more dynamic process in the optical system of the eye perhaps driven by the complicated outer or inner ocular structure.