Macular degeneration affects eye movement behavior during visual search

Stefan Van Der Stigchel,Richard A I Bethlehem,Tos T J M Berendschot,Barrie P Klein,Tanja C W Nijboer,Serge O Dumoulin

doi:10.3389/fpsyg.2013.00579

Abstract

Patients with a scotoma in their central vision (e.g., due to macular degeneration, MD) commonly adopt a strategy to direct the eyes such that the image falls onto a peripheral location on the retina. This location is referred to as the preferred retinal locus (PRL). Although previous research has investigated the characteristics of this PRL, it is unclear whether eye movement metrics are modulated by peripheral viewing with a PRL as measured during a visual search paradigm. To this end, we tested four MD patients in a visual search paradigm and contrasted their performance with a healthy control group and a healthy control group performing the same experiment with a simulated scotoma. The experiment contained two conditions. In the first condition the target was an unfilled circle hidden among c-shaped distractors (serial condition) and in the second condition the target was a filled circle (pop-out condition). Saccadic search latencies for the MD group were significantly longer in both conditions compared to both control groups. Results of a subsequent experiment indicated that this difference between the MD and the control groups could not be explained by a difference in target selection sensitivity. Furthermore, search behavior of MD patients was associated with saccades with smaller amplitudes toward the scotoma, an increased intersaccadic interval and an increased number of eye movements necessary to locate the target. Some of these characteristics, such as the increased intersaccadic interval, were also observed in the simulation group, which indicate that these characteristics are related to the peripheral viewing itself. We suggest that the combination of the central scotoma and peripheral viewing can explain the altered search behavior and no behavioral evidence was found for a possible reorganization of the visual system associated with the use of a PRL. Thus the switch from a fovea-based to a PRL-based reference frame impairs search efficiency.

Highlights

Macular vision is important for tasks that involve high spatial acuity, such as reading and recognizing faces
macular degeneration (MD) patients typically adopt a strategy to direct the eyes such that the image falls onto a peripheral location on the retina to compensate for their impairment: a location on the retina which is not part of the scotoma and which functions as a “pseudo-fovea” (Timberlake et al, 1986, 1987; Whittaker et al, 1988; Fletcher et al, 1999)
SEARCH LATENCY Results show that search latency, defined as the time required to find a target, was longer in the MD group

Summary

Introduction

Macular vision is important for tasks that involve high spatial acuity, such as reading and recognizing faces. When central vision is damaged, e.g., due to macular degeneration (MD), people will miss this location of high visual acuity and experience problems with these high-acuity tasks. The juvenile form of MD occurs in 1 out of 10,000 people (Bither and Berns, 1985), whereas age-related MD is the main cause of diminished visual acuity in the elderly (Leibowitz et al, 1980). MD creates a central visual field scotoma. There is a debate whether this strategy coincides with a reorganization of the visual system (Baker et al, 2005, 2008; Masuda et al, 2008)

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