Application of Repetitive Visual Stimulation to EEG Neurofeedback Protocols

  • Thomas F. Collura


Introduction. This report describes an approach for using repetitive visual stimulation in the context of electroencephalographic (EEG) neurofeedback protocols. The EEG response to repetitive stimulation can be described as a series of successive evoked potentials (EPs), giving rise to a periodic response in the cortex, the steady-state visual evoked potential (SSVEP). Experimental data and signal analyses are presented to support this view. This approach is useful because evoked potential signals reflect sensory and perceptual processes, are sensitive to short-term shifts in attention, and also show important differences between normal and ADD/ADHD groups for example. Methods can be developed to provide real-time measurement and feedback of important variables related to the evoked response. Method. Computerized averaged EP data are compared with filtered EEG “photic driving” responses measured in real time. Synchronous comb-filtering is used to extract real-time SSVEP data which are plotted along with conventional EPs and EEGs. Results are plotted as a time-series and short-term variations are visible. Results. Results of pilot studies are shown, illustrating the ability to record real-time SSVEP’s, and to provide information suitable for to repetitive light flashes may be described as a superposition of successive evoked responses, and do not have to appeal to an “entrainment” model. Shortterm variations in signal amplitude are shown to be sensitive to attentive state, and to reveal moment-to-moment changes in brain responsiveness. Discussion. A basic understanding of the brain’s response to repetitive stimuli can be used to develop a variety of feedback methods. Some of these are identified. The concept of entrainment is discussed and it is shown that neurofeedback with repetitive photic stimulation may be approached without appealing to the notion of a nonlinear response to repetitive stimulation. In our studies the EEG reveals only the expected periodic evoked responses, indicating that the brain is following the stimulus, but not that any lasting or “entrained” frequencies are introduced. Methods that do not rely on the concept of entrainment, but that depend solely on monitoring and feedback of the brain evoked response, provide promising avenues for neurofeedback. Conclusions. This study provides experimental data and a supporting rationale for the use of photic stimulation in EEG neurofeedback. Our approach is based upon an understanding and use of the fact that the EEG response is comprised of a succession of sensory evoked potentials. This is in contrast to methods and models based upon the concept of nonlinear entrainment. A variety of methods for creating neurofeedback protocols are presented and discussed.