Psychophysical measurements of referenced and unreferenced motion processing using high-resolution retinal imaging.

Background: Motion detection thresholds with a stationary frame of reference are significantly lower than unreferencedmotion thresholds. To account for this, previous studies have postulated the existence of compensatory mechanisms, drivenby the presence of a surround, that cancel the effects of eye movements. In the present study we used an adaptive opticsscanning laser ophthalmoscope (AOSLO) to investigate the effects of retinal jitter due to fixation eye movements onreferenced and unreferenced motion thresholds. Methods: The stimuli were produced by modulation of the AOSLO imagingbeam, so that the absolute retinal position of targets was recorded. In Experiment 1 subjects made up/down motionjudgments of a dark horizontal bar presented against a stationary 1-degree bright background. In Experiment 2unreferenced motion thresholds were measured with isolated bright horizontal bars in otherwise complete darkness. Inboth experiments, AOSLO images for each trial were analyzed offline to extract retinal jitter and the retinal position oftargets. Results: For referenced motion, the results were consistent with complete compensation for eye movements by thevisual system. In the unreferenced motion case eye movements adversely affected motion judgments, although there wasevidence of partial compensation for such eye movements. Conclusions: Compensatory processes completely cancel theeffect of fixation jitter for referenced motion but such compensation is partial for unreferenced motion.Keywords: referenced motion, unreferenced motion, fixation eye movements, two-frame motion, adaptive optics, adaptiveoptics scanning laser ophthalmoscope, high-resolution retinal imagingCitation: Raghunandan, A., Frasier, J., Poonja, S., Roorda, A., & Stevenson, S. B. (2008). Psychophysical measurementsof referenced and unreferenced motion processing using high-resolution retinal imaging. Journal of Vision, 8(14):14, 1–11,http://journalofvision.org/8/14/14/, doi:10.1167/8.14.14.