Tracking the eye non-invasively: simultaneous comparison of the scleral search coil and optical tracking techniques in the macaque monkey

Daniel L Kimmel,Dagem Mammo,William T Newsome

doi:10.3389/fnbeh.2012.00049

Abstract

From human perception to primate neurophysiology, monitoring eye position is critical to the study of vision, attention, oculomotor control, and behavior. Two principal techniques for the precise measurement of eye position—the long-standing sclera-embedded search coil and more recent optical tracking techniques—are in use in various laboratories, but no published study compares the performance of the two methods simultaneously in the same primates. Here we compare two popular systems—a sclera-embedded search coil from C-N-C Engineering and the EyeLink 1000 optical system from SR Research—by recording simultaneously from the same eye in the macaque monkey while the animal performed a simple oculomotor task. We found broad agreement between the two systems, particularly in positional accuracy during fixation, measurement of saccade amplitude, detection of fixational saccades, and sensitivity to subtle changes in eye position from trial to trial. Nonetheless, certain discrepancies persist, particularly elevated saccade peak velocities, post-saccadic ringing, influence of luminance change on reported position, and greater sample-to-sample variation in the optical system. Our study shows that optical performance now rivals that of the search coil, rendering optical systems appropriate for many if not most applications. This finding is consequential, especially for animal subjects, because the optical systems do not require invasive surgery for implantation and repair of search coils around the eye. Our data also allow laboratories using the optical system in human subjects to assess the strengths and limitations of the technique for their own applications.

Highlights

The precise measurement of eye position is critical for the study of vision and oculomotor control, as well as related functions such as attention and oculomotor-based behavior
In terms of ring amplitude (Figures 6F,G), we found in both systems that the amplitude of the first phase increased with the size of the instructed saccade (Monkey C: F = 14.0, p < 10−3; Monkey E: F = 43.7, p < 10−10), though the amplitude of ringing was greater in the optical system (Monkey C: F = 11.9, p < 10−3; Monkey E: F = 43.2, p < 10−10) and, in Monkey E only, increased more severely with increasing saccade amplitude than in the coil system (F = 17.7, p < 10−4)
In the varying either the background luminance (vary-BG) experiment, we introduced a step-change in the background luminance while the animal maintained fixation; in the vary-fixation points (FP) experiments, we instead introduced a step-change in the FP luminance, producing luminance changes perhaps more akin to those that would occur within a trial as the subject saccaded between stimuli of differing luminance

Summary

Introduction

The precise measurement of eye position is critical for the study of vision and oculomotor control, as well as related functions such as attention and oculomotor-based behavior. For over 40 years, the principal technique for measuring eye position has been the search coil, in which a small coil of wire is placed on the subject’s eye either embedded in a contact lens (Robinson, 1963; Collewijn et al, 1975) or in non-human studies, surgically implanted in the sclera of the eye (Judge et al, 1980). This system offers high spatial (

Methods

Results

Conclusion