The debate about the nature of fixational eye movements has revived recently with the claim that microsaccades reflect the direction of attentional shifts. A number of studies have shown an association between the direction of attentional cues and the direction of microsaccades. We sought to determine whether microsaccades in attentional tasks are causally related to behavior. Is reaction time (RT) faster when microsaccades point toward the target than when they point in the opposite direction? We used a dual-Purkinje-image eyetracker to measure gaze position while 3 observers (2 of the authors, 1 naive observer) performed an attentional cuing task under three different response conditions: saccadic localization, manual localization, and manual detection. Critical trials were those on which microsaccades moved away from the cue. On these trials, RTs were slower when microsaccades were oriented toward the target than when they were oriented away from the target. We obtained similar results for direction of drift. Cues, not fixational eye movements, predicted behavior.

For reading tasks not involving eye movements, there is an advantage in eccentrically fixating such that text falls in inferior rather than left visual field.

Persons with central field loss must learn to read using eccentric retina. To do this, most adopt a preferred retinal locus (PRL), which substitutes for the fovea. Patients who have central field loss due to age-related macular degeneration (AMD), most often adopt PRL adjacent to and to the left of their scotoma in visual field space. It has been hypothesized that this arrangement of PRL and scotoma would benefit reading. We tested this hypothesis by asking normally-sighted subjects to read with the left or right half of their visual field plus 3.2 degrees in the contralateral field masked from view. Letter identification, word identification, and reading were all slower when only the information in the left visual field was available. This was primarily due to the number of saccades required to successfully read to stimuli. These data imply that patients would be better off with PRL to the right of their scotoma than to the left for the purposes of reading.

Short segments of two TV programs without audio description (AD) were presented to 25 subjects with low vision and 24 subjects with normal vision, and 29 additional subjects heard only the standard audio portions. The subjects then answered questions based on the visual information contained in the AD of the programs. The subjects with normal vision performed the best, followed by those with low vision and those who heard only the audio portion; all performed at better than chance levels. The results indicate that although AD may provide information on visual details to visually impaired audiences, some of the information in the AD may be obtained from the standard audio portion.

Visually impaired observers read dynamically displayed text faster than text displayed in a normal page view. The goal of this study was to compare reading rates from two dynamic-presentation methods that have been proposed to facilitate reading from computer-based displays. Prior research has shown that both normally sighted and low-vision observers read text displayed to the same location, one word at a time [known as rapid serial visual presentation (RSVP)], faster than a page of text. A similar comparison with text scrolled continuously across the screen also shows faster reading for low-vision patients, but the relative change from a standard page view is substantially less (15% faster for the scroll display versus 80% faster for RSVP). In this study we directly compared these techniques. For those with normal vision, reading from the RSVP display was 1.3 times faster than reading from the scroll display [t(9) = 3.32, P = 0.009]. Although the difference in reading rates for the visually impaired group did not reach statistical significance, as a group they read 13% slower from the RSVP than from the scroll display.

No abstract

Reading rates are slower for persons with low vision than for normally-sighted persons. This study investigated the change in reading performance and reading eye movements when we simulated the two most common causes of low vision--central field loss and cataract--and their combination (scotoma + cataract). Three subjects read sentences with each of these simulated impairments at five different letter sizes. They required larger letters to read with the cataract or scotoma than they did with normal vision, and larger still to read with scotoma + cataract; the change in eye movements relative to normal vision was similar across conditions. When reading large letters (1.61 degrees), the cataract had almost no effect, while the scotoma and scotoma + cataract reduced reading rate for two of the subjects. The cataract had a greater impact on performance relative to normal vision for these same two subjects, while for the third subject the cataract had a greater impact with the scotoma in place. Cataract extraction tends to be postponed in patients with central field loss because it is not perceived to be beneficial. The findings from this study, as well as others, suggest that patients with central field loss would benefit from cataract extraction.

When the center of a readers, visual field is blocked from view, reading rates decline and eye movement patterns change. This is true whether the central visual field is blocked artificially (i.e. a mask) or through disease (e.g. a retinal scotoma due to macular degeneration). In past studies, when mask size was defined in terms of the number of letters masked from view, reading rates declined sharply as number of letters masked increased. Patients with larger central scotomas (in degrees of visual angle) also read slower. We sought to determine whether number of letters masked or size of the mask in degrees is the predominant factor affecting reading rates and eye movement behavior. By matching number of letters masked across several mask sizes (and compensating for reduced acuity in the periphery), we found that number of letters masked is the more important factor until mask size is quite large (> or = -7.5 degrees) and number of letters masked from view is more than seven.