Fixation light hue bias revisited: Implications for using adaptive optics to study color vision

Abstract

Current vision science adaptive optics systems use near infrared wavefront sensor ‘beacons’ that appear as red spots in the visual field. Colored fixation targets are known to influence the perceived color of macroscopic visual stimuli(Jameson, D. and Hurvich, L. M., 1967. Fixation-light bias: an unwanted by-product of fixation control. Vis. Res. 7, 805 – 809.), suggesting that the wavefront sensor beacon may also influence perceived color for stimuli displayed with adaptive optics. Despite its importance for proper interpretation of adaptive optics experiments on the fine scale interaction of the retinal mosaic and spatial and color vision, this potential bias has not yet been quantified or addressed. Here we measure the impact of the wavefront sensor beacon on color appearance for dim, monochromatic point sources in 5 subjects. The presence of the beacon altered color reports both when used as a fixation target as well as when displaced in the visual field with a chromatically neutral fixation target. This influence must be taken into account when interpreting previous experiments and new methods of adaptive correction should be used in future experiments using adaptive optics to study color.

Adaptive optics without altering visual perception

“…While this strategy allows excellent optical correction, so long as the distance between the beacon and stimulus is on the order of 1° or less (Bedggood, Daaboul, Ashman, Smith, & Metha, 2008), even a dim, displaced beacon can significantly impact perception. For example, Hofer et al (2012) found that a 1 μW, 840 nm beacon caused significant shifts in red-green appearance for small point stimuli, similar to those previously described for large stimuli when using colored fixation targets (Jameson and Hurvich, 1967). …”

“…We modified an existing adaptive optics system (Hofer, et al 2012) to accommodate a long wavelength 980 nm beacon (super luminescent diode, SLD, QPhotonics LLC) instead of the original, more typical, 840 nm beacon (SLD, Volga Technology Ltd.). Figure 1 describes the current system.…”

“…A total of five subjects participated, subjects 1 and 2 were chosen because the original 840 nm wavefront-sensing beacon was known to impact their color reports in a prior study (Hofer et al 2012), while subjects 3-5 were new recruits. Subjects 1 and 4 were the authors and subjects 3 and 5 were practiced psychophysical observers naïve to the purposes of this study.…”

“…Subjects rated color appearance with the 5 color name method described by Hofer et al (2012) and Koenig and Hofer (2012). Briefly, subjects were instructed to rate seen stimuli according to hue and saturation, and not brightness, by distributing 10 key presses among five categories: white, green, blue, yellow, or red; in any manner they felt best reflected the appearance of the stimulus on each trial (Koenig & Hofer, 2012).…”

“…This potential is hampered, however, by visual interference from the wavefront-sensing beacon used during correction. For example, we have previously shown that even a dim, visible beacon can alter stimulus perception (Hofer, H. J., Blaschke, J., Patolia, J., & Koenig, D. E. (2012). Fixation light hue bias revisited: Implications for using adaptive optics to study color vision.…”