The Journal of general physiology
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The changes in pupil size were recorded by infrared pupillographic methods in response to light flashes of different durations and intensities for a 13 degree 34 minute centrally fixated circular field. For such stimuli, the threshold intensities for (rod) vision and for the pupil response were found to be about the same. ⋯ A similar dichotomy appears in curves relating response amplitude to response latency. Since the pupil response is determined by total flash energy, intense long flashes produce larger pupil responses than shorter (and perceptually brighter) ones of the same intensity.