ELECTROPHYSIOLOGICAL CORRELATES OF FLICKER-INDUCED FORM HALLUCINATIONS

  • Deirdre Twomey
  • Mark Glennon
  • Mark A. Elliott

Abstract

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 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.

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