Perceptual cycles travel across retinotopic space

Visual perception waxes and wanes periodically as a function of the phase of low-frequency brain oscillations (theta, 4-7 Hz; alpha, 8-13 Hz). Perceptual cycles are defined as the corresponding periodic modulation of perceptual performance. Here, we tested the hypothesis that brain oscillations travel across the visual cortex, leading to predictable perceptual consequences across the visual field, i.e., perceptual cycles travel across the retinotopic visual space. An oscillating disk (inducer) was presented in the periphery of the visual field to induce brain oscillations at low frequencies (4, 6, 8 or 10 Hz) at a specific retinotopic cortical location. Target stimuli at threshold (50% detection) were displayed at random times during the periodic disk stimulation, at one of three possible distances from the disk. Electroencephalography (EEG) was recorded while participants performed a detection task. EEG analyses showed that the periodic stimulation produced a complex brain oscillation composed of the induced frequency and its first harmonic likely due to the overlap of the periodic response and the neural response to individual stimuli. This complex oscillation, which originated from a precise retinotopic position, modulated detection performance periodically at each target position and at each frequency. Critically, the optimal behavioral phase, i.e., of highest performance, of the 8 Hz and 10 Hz oscillations (alpha range) consistently shifted across target distance to the inducer. Together, the results demonstrate that alpha-induced perceptual cycles travel across the retinotopic space in human observers at a propagation speed ranging from 0.3 to 0.5 m/s. Significance Statement Visual perception is modulated periodically as a function of the phase of theta-alpha brain oscillations in the occipital cortex, i.e., perceptual cycles. We hypothesized that brain oscillations travel across the visual cortex, which in turn would result in the propagation of perceptual cycles across the retinotopic visual space. Using psychophysics coupled with EEG recordings, our study showed that the phase of alpha brain oscillations associated with the highest visual performance consistently shifted across the visual space. Perceptual cycles traveled across the retinotopic space in human. The propagation speed ranged from 0.3 to 0.5 m/s consistent with the conduction delay of long-range lateral connections.