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Jeffrey B. Mulligan; Assessing visual delays using pupil oscillations. Journal of Vision 2011;11(11):504. doi: 10.1167/11.11.504.
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© ARVO (1962-2015); The Authors (2016-present)
Stark (1962) demonstrated vigorous pupil oscillations by illuminating the retina with a beam of light focussed to a small spot near the edge of the pupil. Small constrictions of the pupil then are sufficient to completely block the beam, amplifying the normal relationship between pupil area and retinal illuminance. In addition to this simple and elegant method, Stark also investigated more complex feedback systems using an electronic “clamping box” which provided arbitrary gain and phase delay between a measurement of pupil area and an electronically controlled light source. We have replicated Stark's results using a video-based pupillometer to control the luminance of a display monitor. Pupil oscillations were induced by imposing a high-gain linear relationship between pupil area and display luminance, with a variable delay. A simple model, in which the pupil responds linearly to retinal illuminance with a fixed delay, predicts that the period of oscillation will be linearly related to the applied feedback delay, with a slope of 2, and an x-intercept corresponding to the internal delay. Slopes of the period-vs-delay function for 3 subjects are close to the predicted value of 2 (1.96–2.39), and the implied delays range from 254 to 376 milliseconds. Our setup allows us to extend Stark's work by investigating a broader class of stimuli.
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