Purchase this article with an account.
H. J. Hofer, J. Blaschke, J. Patolia, D. E. Koenig; Fixation Light Hue Bias and Adaptive Optics Psychophysics: Does the Wavefront Sensor Beacon Alter Color Appearance?. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6290.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Adaptive optics (AO) imaging combined with psychophysics is uniquely suited for investigating receptoral and neural limits on visual perception. However, current systems rely on a salient red correction beacon that may influence stimulus apparent color. Despite its importance for proper interpretation of previous and future AO 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.
We used both color-naming (2 subjects) and hue-scaling (3 subjects) to measured the impact of a dim, red AO beacon (840 nm, ~1υW) on the appearance of dim, brief (6 or 34 msec), monochromatic (575 or 580 nm) small spot stimuli. Stimuli were displayed either with conventional refraction (2mm pupil, ~1’ on the retina) or static correction of higher order aberrations (6mm pupil, ~0.5’) in the central fovea or at 1°. Appearance was compared with and without the AO beacon (~1° - 1.5° from the stimulus, a typical AO configuration). Subjects fixated a dim white point or, for foveal stimuli, midway between two dim white dots separated by ~2.25°. We also measured the impact of fixating the AO beacon or replacing the foveal target with two red fixation points (2 subjects). Experiments were performed dark adapted (fovea) or on the ‘cone plateau’ in an empty visual field except as described above.
In the color-naming experiment there was a slight, but insignificant, trend to report more green spots with the beacon present. In the hue-scaling experiments, which also assess changes in saturation as well as more finely probe changes in hue within a category, the beacon caused 2 of 3 subjects to rate spots significantly greener, with larger effects for dimmer spots. Fixating the red beacon (or between 2 red fixation points) had a more dramatic yet opposite affect, with mean reported hue shifting remarkably in the red direction, for both response frameworks.
The AO beacon significantly impacts color appearance for small spot stimuli. Apparent hue is markedly more similar to that of the beacon when fixated, with an opposite and more modest effect with a visible beacon that is not fixated. These results appear to reflect a critical role of endogenous attention on apparent color for these stimuli. We conclude that it is inappropriate to use visible colored beacons or imaging lights in color-related AO experiments. Alternative methods, such as longer wavelength beacons or sensor-less schemes must be employed.
This PDF is available to Subscribers Only