A study of critical fusion frequency and duty ratio with multiple light stimuli

In recent years, many studies have focused on the importance of the temporal domain in the visual system. Critical fusion frequency (CFF) is the threshold value at which a flickering stimulus appears to be a steady stimulus. Therefore, the CFF has been extensively used to evaluate the visual temporal processing. However, there are unexplained aspects of this perceptual phenomenon. Our previous results have shown that by measuring the duty ratio dependence of CFF in detail, the profile of the CFF has an asymmetric characteristic curve. In this study, we examined the effect of multiple flashing stimuli on the CFF-duty ratio profile. In our experimental approach, CFF values were measured for each duty ratio using a 3x3 grid of flashing LEDs. An analog signal output device was used to drive them and control the flashing frequency, switch the duty ratio, and record the perceived CFF threshold value. The 3x3 grid stimuli are also synchronized by being driven by a transistor circuit. As a result, we observed that the asymmetry of the CFF-duty ratio profile tended to mitigate to symmetry in the 3x3 grid stimulus compared to previous experiments with a single LED flashing stimulus. We quantified the degree of symmetry by normalizing the measurements in the two presented stimuli and found that the 3x3 grid stimuli were approximately the same or more symmetric than the single stimulus. Specifically, for the 3x3 grid stimuli, a decrease of about 5% in the normalized CFF value, a factor affecting symmetry, was observed for curve duty ratios ranging from 20% to 40%. Furthermore, this result fits our theoretical model and the symmetry parameter appears in our mathematical formalism reported in our study.