Andrew Zavala¹, Paul Dassonville¹; ¹University of Oregon

Neural oscillations in the alpha-band frequency have been purported to gate perception through alternating states of neural excitation and inhibition. These alternations are theorized to modulate perceptual outcomes such as target detection thresholds and perceived timing (Mathewson et al., 2012). Does this feature of the visual system extend to the ability to localize moving targets? And can it provide an explanation for the Fröhlich effect, where an observer mislocalizes the starting location of a moving object in the direction of motion? In an initial experiment, participants reported the location of the starting point of a moving target that was presented after an auditory entrainment of alpha at 8.5 or 11.5 Hz. The magnitude of the Frölich effect was significantly smaller with the 11.5 Hz entrainment, suggesting that the faster alpha rhythm accelerated perceptual processing and allowing target localization earlier in its trajectory. However, the illusion magnitude was not modulated by alpha phase at target onset for either frequency. To ensure that entrainment was successful, a second experiment used audio-visual entrainment to test whether the Fröhlich effect would be modulated by alpha phase and included an additional task that has been used to demonstrate a modulation of the two-flash fusion effect with alpha phase (Ronconi et al., 2017). A Fast Fourier analysis replicated the finding of an alpha modulation of the two-flash fusion effect but again found no evidence that the Fröhlich effect is modulated by alpha phase. Our results provide some evidence that the Fröhlich effect is influenced by entrainment frequency, but not in a way that is detectable by phase alignment. It is possible that the illusion is partly the result of visual sampling delays driven by the alpha rhythm, but that this effect is diluted by additional mechanisms that impact higher levels of perceptual processing (e.g., motion extrapolation).