Elisabeth M. Fine

Fixational Eye Movements Are Not an Index of Covert Attention

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.

Reading with simulated scotomas: attending to the right is better than attending to the left

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.

Scrolled and rapid serial visual presentation texts are read at similar rates by the visually impaired

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.

Reading with eccentric fixation is faster in inferior visual field than in left visual field.

Purpose People with central field loss tend to fixate so that information falls in the inferior or left visual field. Studies of reading from a page of text suggest that using inferior field is advantageous relative to using left visual field. In this study, we investigated whether reading without eye movements in normal peripheral vision is better when text is presented in inferior or left visual field. Methods Reading rates were determined for retinally stabilized rapid serial visual presentation sentences of seven letter sizes, presented at 5° in inferior and left visual field of six normal observers. Results When print size is appropriately magnified for peripheral viewing, reading speed in inferior field is faster than in left visual field. There is no significant difference between inferior and left visual field in the print size required to reach maximum reading speed. Conclusions 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.

Reading with central field loss: number of letters masked is more important than the size of the mask in degrees.

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.

The effects of simulated cataract on reading with normal vision and simulated central scotoma

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.

The Role of Context in Reading with Central Field Loss

It has been suggested that readers with central field loss (CFL) may not be able to use context to facilitate reading in the same way that normally sighted readers do because their processing capacity is fully utilized decoding the degraded visual stimulus. If true, this could account for their slow reading, even when text is appropriately magnified. Readers with CFL and normally sighted, age-matched controls read sentences and lists of random words from two dynamic text displays. We used sentence-gain (the ratio of reading rates for sentences to random words) to assess the use of context. Sentence-gain was equivalent across groups. Therefore, reduced reliance on context cannot explain the slower reading rates of people with CFL.

Enhancement of text for the visually impaired

Previous research has established the benefits of image enhancement by spatial filtering for face perception and motion video appreciation among elderly low-vision observers [Invest. Ophthalmol. Vis. Sci. 32, 2337 (1991); J. Opt. Soc. Am. A 11, 1929 (1994)]. It has also been reported that similar enhancement could increase reading speeds by a factor of 2-4 in the same population [cf. Ophthalmology 96, 115 (1989)]. In our experiments we sought to determine what benefit, if any, was derived from spatial filtering of text for low-vision readers. Results from this series of studies indicate that 66% of patients do increase their reading rate with enhancement, but this increase is small. Change in reading rate with spatial filtering ranged from a 100% decrement to a 125% improvement, with an average 13% improvement. Only 10 of 67 subjects increased their reading rates by 50% or more. The clinical information that we gathered does not allow us to predict accurately which patients will benefit from spatial filtering. On the basis of these findings we conclude that enhancement of text by spatial filtering does not substantially increase reading rates for most low-vision patients.

Are the Benefits of Sentence Context Different in Central and Peripheral Vision

BACKGROUND Sentence context increases reading speed relative to reading unrelated words. Previous studies of normal peripheral retina and in patients with central field loss (CFL) have come to different conclusions regarding the benefits of sentence context for reading in peripheral retina. Studies of normal peripheral vision presented the text to inferior visual field; it is presumed that most of the patients fixated using retina lateral to their scotoma. The goal of the current study was to determine whether the location of the text on the retina interacts with the usefulness of sentence context. METHODS Normally sighted subjects read sentences and random lists of words presented at the fovea and at 50 to the left of and 50 inferior to fixation in visual field space. Texts were presented using rapid serial visual presentation (RSVP). RESULTS The ratio of reading rates for sentences to random words (context gain) was the same in the inferior field (2.7 +/- 0.20) and at the fovea (2.6 +/- 0.26); context gain was greater in the left field (7.2 +/- 1.22). CONCLUSIONS Sentence context increases reading speed regardless of the position of the text on the retina. Reading rates in peripheral retina are not decreased because of an inability to use sentence context.

Effects of cataract and scotoma on visual acuity: a simulation study.

Central field loss (CFL) and cataract both decrease visual acuity. For patients with CFL, visual acuity is further reduced when the acuity target is more visually complex. We tested visual acuity for targets of varying complexity (letters alone, letters flanked by one or two xs on each side, and words) in subjects with normal vision and in the presence of a simulated cataract, simulated scotoma, and their combination (scotoma + cataract). Visual acuity was best with normal vision and worst with scotoma + cataract for all of the acuity targets. There was little difference in visual acuity between the letters alone and flanked letters, and visual acuity was best for words under all vision conditions. The cataract had a greater impact on visual acuity when the subjects central visual field was clear (normal vision) than when it was occluded by the simulated scotoma.