Electrophysiological correlates of flicker-induced form hallucinations
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Twomey, D., Glennon, M., & Elliott, M.A. (2010). Electrophysiological correlates of flicker-induced form hallucinations. In Bastianelli, A., & Vidotto, G., (Eds.) Fechner Day 2010. Proceedings of the 26th Annual Meeting of the International Society for Psychophysics, Padova, Italy: The International Society for Psychophysics.
Form hallucinations can be reliably induced using temporally modulated light within a specific frequency range (15-30Hz). The neural substrates of such states have yet to be established with certainty. Brain activity of 5 "high responders" was recorded as they completed a visual report paradigm in flickering Ganzfeld (FGF) conditions. Illusory geometric forms were induced via stimulation of the Ganzfeld with rapid and intermittent square-wave light pulses of 3,000 cd/m2 at 15-30Hz. On experiencing a specified target form (point, rectangle, spiral or circle) a left index button press was made to terminate the flicker presentation. A synchronization of activity in the theta (3.5-7Hz) and gamma (30-70Hz) frequency bands reflective of top-down and bottom-up processing respectively may enable the apperception of geometric form.