Flicker photometry: residual minimum flicker

We show that when all possible optical artifacts are eliminated in a flicker photometric procedure, there is still a residual minimum flicker after color fusion occurs. The stimuli were alternated with approximately rectangular counterphase pulses and we obtained results contrary to those of a previous report where the stimuli were alternated sinusoidally. In a subsidiary test using a computer-generated counterphase cosine wave on an RCB monitor, at 70 td, one observer perceived no residual flicker but a second observer did.