JT Pirog¹ (), Jingye He¹, William Tuten¹; ¹University of California, Berkeley

Psychophysical evidence shows that exposure to luminance flicker reduces sensitivity to subsequent luminance modulations, likely reflecting contrast adaptation that has been observed physiologically in subcortical magnocellular neurons. Here, we investigate how luminance flicker influences the visibility of small, diffraction-limited flashes, subtending <10 foveal cones. We used an adaptive optics scanning laser ophthalmoscope (AOSLO) to present narrowband (543 nm, “green”) increments of various diameters (1 to 23 arcmin) for 200 ms to the fovea following the delivery of isochromatic luminance (orange) flicker comprised of cycling the red (680 nm) and green AOSLO primaries in phase at 3.75 Hz. The initial adaptation period spanned 30 seconds, with one second of top-up adaptation inserted between each one-second trial. We measured detection thresholds across a range of stimulus onset asynchronies (SOAs; 33 to 500 ms) in 3 subjects. Control measurements were also obtained without exposure to flicker. We found that the visibility of large spots (23 arcmin) was reduced at all tested SOAs following flicker adaptation. With small spots (1 arcmin), a different pattern was observed: visibility after adaptation to identical flickering conditions was similar to control at the shortest and longest SOAs, and sensitivity was improved by ~25% from control over a range of intermediate SOA values (100 to 200 ms). Our results are corroborated by recent findings from retinal physiology showing opposing patterns of SOA-dependent sensitivity changes in magnocellular and parvocellular neurons following exposure to luminance flicker. Future work will include measurements of chromatic identification thresholds following flicker to further parse the contributions of the chromatic and luminance channels to processing very small stimuli approaching the neural grain of the foveal receptor array.

Acknowledgements: This work was supported by the Air Force Office of Scientific Research (FA9550-20-1-0195, FA9550-21-1-0230), the National Institutes of Health (R01EY02359, T32EY007043), the Hellman Fellows Fund, and the Alcon Research Institute.