Work & Projects
Early days. One rotation project done, many more questions to go.
Do Microfluctuations Increase When Chromatic Aberration Cues Are Reduced?
Chromatic aberration is considered a directional cue that helps drive accommodation: because the eye focuses different wavelengths at slightly different depths, the resulting blur signal gives the visual system information about which way to adjust focus. This project asked what happens when that cue is degraded. By manipulating the red/blue ratio of a target, chromatic aberration information can be systematically reduced. At the extremes of the ratio (pure red or pure blue), there is very little wavelength contrast, meaning the chromatic cue is weakest. If microfluctuations serve as a search signal that helps the eye find the correct focal plane, then reducing chromatic information should force the system to rely more on them, and their power should rise. This predicts a U-shaped relationship between red/blue ratio and microfluctuation power, with the highest power at the edges where chromatic information is least available. Using data from a previous experiment, I analysed microfluctuation power across 10 chromatic conditions and 3 target distances (1.5D, 2.5D, 3.5D), with 180 trials per subject.
The results showed a significant effect of target distance on microfluctuation power (p<0.01): farther targets produced larger fluctuations. However, there was no significant effect of chromatic content (p=0.98). The U-shaped pattern was not observed across any distance condition. This suggests that, at least under these conditions, microfluctuation power does not appear to increase in response to reduced chromatic aberration cues in the way the hypothesis predicted.
Microfluctuations in Ocular Accommodation Across Target Distance and Light Spectrum
Nitin Negi¹, Benjamin Chin¹ — ¹Rochester Institute of Technology
The human visual system uses a process known as accommodation to achieve clear images on the retina. Accommodation dynamically changes the shape of the crystalline lens, thus adjusting the eye's refractive power. Notably, accommodation is not stable. Even under steady viewing conditions, the visual system exhibits temporal variations in accommodation known as microfluctuations. A longstanding hypothesis in vision science is that low-frequency components of microfluctuations generate odd-error feedback signals that assist with accommodation. We further hypothesize that the visual system may increase its microfluctuations under conditions when accommodation is more difficult, such as when light entering the eye is narrowband.
We tested this hypothesis with an existing dataset (Chin et al., 2025) of continuous accommodation measurements in which participants viewed small (~1°), foveally presented words for 3 seconds. The light spectra of stimuli were varied by mixing pairs of narrowband display primaries with varying ratios of the red and blue primaries. The green primary was either absent or fixed to half the luminance of the other two primaries. Each subject completed 216 trials corresponding to 12 unique spectra, 3 target distances (1.5, 2.5 and 3.5 D), and 6 trials per combination of spectrum and distance. Accommodative state was quantified as defocus aberration in the eye's wavefront, which was recorded at 30 Hz with a Shack-Hartmann wavefront sensor.
We calculated total power in the low frequency components (0.1–0.6 Hz) on each trial via a power spectrum analysis of the time series, then averaged across all trials and participants for each combination of spectrum and accommodative distance. A two-factor repeated measures ANOVA indicated a significant effect of target distance on microfluctuations (F(2,180)=4.99, p<0.01), but not of color (F(9,180)=0.29, p=0.98). There was no interaction between the two factors (F(18,180)=0.2, p=1.0). Future work will explore the potential impact of other factors on microfluctuations.
Acknowledgements: Startup funds from the Chester F. Carlson Center for Imaging Science, Rochester Institute of Technology.
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