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Kenneth Alexander, Michael W. Levine; Temporal frequency characteristics of period doubling in the cone flicker ERG. Journal of Vision 2002;2(10):108. doi: 10.1167/2.10.108.
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ERG responses of the cone system to flickering stimuli often exhibit a cyclic variation in amplitude (period doubling) that has been attributed by Crevier and Meister (1998) to an early retinal nonlinear feedback mechanism that alters response gain. To investigate this phenomenon further, we examined the temporal frequency characteristics of ERG period doubling in a group of 12 visually normal control subjects using sinusoidally flickering stimuli and spectral analysis of the ERG responses. Period doubling was most evident at temporal frequencies near 30 Hz, and there was considerable intersubject variation in the magnitude of the effect. For all subjects, ERG responses were characterized by a harmonic component at the stimulus frequency, as well as higher harmonics that were even and odd multiples of the stimulus frequency, consistent with previous studies. For the 6 subjects who demonstrated period doubling, there were also harmonic components at even and odd multiples of a frequency that was half the stimulus frequency (subharmonic), although there was little evidence of the subharmonic itself. The results are consistent with a model of the generation of the cone system ERG in which an early nonlinear mechanism produces a subharmonic prior to the site that generates the higher harmonics of the ERG response, with a subsequent bandpass filter that preferentially attenuates the subharmonic. Intersubject variation in the magnitude of the period doubling effect may represent differences in the strength of a nonlinear feedback signal.
Crevier, D. W., & Meister, M. (1998) Synchronous period-doubling in flicker vision of salamander and man. Journal of Neurophysiology, 79, 1869–1878.
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