APPLICATION OF FOURIER ANALYSIS TO FLICKER PERCEPTION Anderson Rodrigues1, Eline Melo1,2 & Claudio Teixeira1-3* 1Núcleo de Medicina Tropical, Universidade Federal do Pará, Belém, Brazil 2Centro de Ciências Biológicas e da Saúde, Universidade da Amazônia, Belém, Brazil 3Centro Universitário do Estado do Pará, Belém, Brazil * cecteixeira@pq.cnpq.br The sensitivity to visual contrast of a luminous stimulus is determined by the amplitude of the fundamental Fourier component of the waveform at various spatial frequencies (Campbell and Robson, 1968; Figure 1). On the other hand, interactions between the center and the periphery of neural fields determine the patterns of neural and perceptual response to the same set of luminous stimuli (Kremers et al., 2004, Teixeira et al., 2014; Figure 2). In this context, we test the hypothesis that such center-peripheral interactions are the neural mechanisms evidenced by Campbell and Robson. BACKGROUND To this purpose, we quantified the perceived flicker strength (PFS) in the center of a test stimulus, which luminance was simultaneously modulated with a surround stimulus (Figure 3). The luminance modulation depth of a separate stimulus, identical to the center test stimulus but without the surround, was determined using a two-alternative forced choice procedure. The PFS was measured with no temporal phase differences between center and surround stimuli. METHODS Results show that (Figure 4): (i) there is a decrease in PFS when either sinusoidal center-peripheral stimuli or rectangular center-peripheral stimuli have the same contrast; (ii) there is a decrease in PFS, smaller than (i), when either a central sinusoidal stimulus and a rectangular peripheral stimulus or a central rectangular stimulus and a sinusoidal peripheral stimulus have the same contrast; (iii) there is a decrease in PFS, similar to (i) and larger than (ii), when either a central sinusoidal stimulus and a rectangular peripheral stimulus or a central rectangular stimulus and a peripheral sinusoidal stimulus have contrast levels differing by 4/π times. RESULTS CONCLUSION In general, these results suggest that the strength of interactions between the center and the periphery of neural fields can be determined by the fundamental Fourier component of the waveform of the visual stimuli (Figure 5). 1. Campbell & Robson. (1968). J. Physiol., 197, 551-566. 2. Kremers et al. (2004). J. Vis., 4, 643-63. 3. Teixeira et al. (2014). J. Vis., 14(9): 10, 1–18. REFERENCES FIGURE 3 FIGURE 2 Source: Kremers et al., 2004. FIGURE 1 Time Amplitude FIGURE 4 FIGURE 5 Supported by CNPq (Brazil)