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. 2006 Sep;47(9):4152-9.
doi: 10.1167/iovs.05-1672.

Use of an Augmented-Vision Device for Visual Search by Patients With Tunnel Vision

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Free PMC article

Use of an Augmented-Vision Device for Visual Search by Patients With Tunnel Vision

Gang Luo et al. Invest Ophthalmol Vis Sci. .
Free PMC article

Abstract

Purpose: To study the effect of an augmented-vision device that superimposes minified contour images over natural vision on visual search performance of patients with tunnel vision.

Methods: Twelve subjects with tunnel vision searched for targets presented outside their visual fields (VFs) on a blank background under three cue conditions (with contour cues provided by the device, with auditory cues, and without cues). Three subjects (VF, 8 degrees -11 degrees wide) carried out the search over a 90 degrees x 74 degrees area, and nine subjects (VF, 7 degrees -16 degrees wide) carried out the search over a 66 degrees x 52 degrees area. Eye and head movements were recorded for performance analyses that included directness of search path, search time, and gaze speed.

Results: Directness of the search path was greatly and significantly improved when the contour or auditory cues were provided in the larger and the smaller area searches. When using the device, a significant reduction in search time (28% approximately 74%) was demonstrated by all three subjects in the larger area search and by subjects with VFs wider than 10 degrees in the smaller area search (average, 22%). Directness and gaze speed accounted for 90% of the variability of search time.

Conclusions: Although performance improvement with the device for the larger search area was obvious, whether it was helpful for the smaller search area depended on VF and gaze speed. Because improvement in directness was demonstrated, increased gaze speed, which could result from further training and adaptation to the device, might enable patients with small VFs to benefit from the device for visual search tasks.

Figures

Figure 1
Figure 1
An augmented-vision head mounted display system for the left eye. A miniature camera captures video images of the ambient scenes, and the contour images of the scenes are shown in an optical see-through display. The user can see the minified contour images and the ambient scene through the display simultaneously. The nose-pad mount provides easy adjustments of monocular pupilary distance, height, and vertex distance.
Figure 2
Figure 2
A diagram of the visual search task performed by subjects with tunnel vision. Targets were presented outside their VFs. Auditory cues were provided by buzzers placed around the projection screen, which indicate the approximate directions of targets, but not their eccentricities. The minified contour images seen in the HMD provided cues for both the direction and eccentricity of targets.
Figure 3
Figure 3
An example of horizontal and vertical gaze movements in a visual search trial. S and E indicate the moments at which the subject started to move his gaze and started to fixate on a target, respectively. The segment between them was extracted for performance analysis.
Figure 4
Figure 4
A diagram of the definition of the directness measure used in this study. The dashed curve represents a gaze trajectory, Pi and Pi+1 are two consecutive sample points on the trajectory. Directness of the whole search path is calculated as an average of cos(θ) weighted by step length over the whole path from S to E.
Figure 5
Figure 5
Visual search time of the three subjects in the larger area search (study A). Auditory cues and contour cues significantly reduced search time for all subject. Error bars represent SEM.
Figure 6
Figure 6
Relative improvement with contour cues in study B. Data points are ratios of search time without cues divided by time with contour cues. Visual inspection suggests that when the VF was larger than 10º, contour-cue search was usually faster than without-cue search.
Figure 7
Figure 7
Search times of smaller-area search (66º by 54º, study B). With contour cues, the small-VF group (VF<10º, n=3, solid symbols) needed more time, but the large-VF group (VF≥10º, n=6, open symbols) needed less time than without cues. Auditory cues significantly reduced search time. Times with auditory cues are plotted for all eccentricities combined. Error bars represent SEM.
Figure 8
Figure 8
Directness of visual search. (a) Directness of the 3 subjects in the larger-area search (study A); (b) Mean directness of the 9 subjects in the smaller area search (study B). Overall the directness in study B was better than that in study A, in which the search area was about twice as large. In both studies, directness with either auditory or contour cues was better than that without cues. Error bars represent SEM. Note that the directness of normally sighted people is nearly 1.0.
Figure 9
Figure 9
Search time versus product of directness and speed. Data points are from the 9 subjects for 15º, 22º, and 29º eccentricities in without-cue, auditory-cue, and contour-cue searches.
Figure 10
Figure 10
Predictions based on regression model Eq. 2 and calculated using Eq. 4. Eccentricity threshold indicates an area within which patients could search faster with the device than without it. An increase in gaze speed with contour cues may permit a larger beneficiary area (e.g. A to B), and make the device useful for patients with smaller VF (e.g. C to D). The ratio of eccentricity threshold to VF radius is plotted with x and open triangle symbols, which represents expansion ratio of the HMD device. The device might provide larger expansion ratios to patients with smaller VFs than those with larger VFs.

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