Single-channel sinusoidally modulated visual-signal generator with variable temporal contrast

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Abstract
A novel technique is presented for sinusoidal temporal modulation of a light stimulus. The instrument consists of a linear polarizer, a quarter-wavelength retarder, and a rotating polarizer-analyzer. One advantage of using this technique over conventional single-channel polaroid techniques is that one can adjust the depth of modulation while maintaining a constant average intensity. Two separate and differing calculations are presented to show that the output is theoretically a pure sinusoid modulation in time, with a constant average intensity. Results of experimental verifications are included.