Superposition model for Steady State Visually Evoked Potentials

Abstract

Abstract-Steady State Visually Evoked Potentials (SSVEP)are signals produced in the occipital part of the brain when someone gaze a light flickering at a fixed frequency. These signals have been used for Brain Machine Interfacing (BMI), where one or more stimuli are presented and the system has to detect what is the stimulus the user is attending to. It has been proposed that the SSVEP signal is produced by superposition of Visually Evoked Potentials (VEP) but there is not a model that shows that. We propose a model for a SSVEP signal that is a superposition of the response due to the rising and falling edges of the stimulus and that can be calculated for different frequencies.We fixed the model for 4 subjects that gazed stimuli in the frequencies of 9Hz, 11Hz, 13Hz and 15Hz, and duty-cycles of 20%, 35%, 50%, 65%, and 80%. Since the phases of SSVEP signals are stable over the time, these were used to fix the model, without the amplitude; however, signals of scattered phases were discarded. The model parameters were found using the Oz electrode signals and a genetic algorithm.The mean absolute error (MAE) between the measured phase and the obtained one was calculated for each subject (named S1, S2, S3, and S4). The model was fixed for the subjects in the fundamental frequencies, just two of them in the second harmonic, and one in the third harmonic. We obtained a maximum MAE for 3 subjects (S1, S2, and S4) in the fundamental frequencies at 0.30 rad and one of them (S2) with 0.21 rad in the second harmonic. The last one (S3) signals show poor results with a MAE between 0.46 rad and 1.79 rad by including fundamental frequencies, and second and third harmonics. The results show similarities among the different model parameters such that it suggests that a general model could be obtained.

Multisensory Flicker Modulates Widespread Brain Networks and Reduces Interictal Epileptiform Discharges in Humans

“…Next, we tested potential mechanisms by which flicker induces a steady-state EP. One common hypothesis is that the steady-state EP results from the linear superposition of single pulse EPs 41,60,61 (Figure 4A). This contrasts with another proposed mechanism, in which the steady-state EP results from intrinsic properties of circuits which have greater responses to specific stimulation frequencies.…”

Modelling the brain response to arbitrary visual stimulation patterns for a flexible high-speed BCI

“…In this paper, we presented a method that models the process of VEP generation and can be used in two directions to either predict the EEG response to a visual stimulation pattern (Code2EEG) or predict the visual stimulation pattern from the EEG (EEG2Code). Contrary to previous methods (Thielen et al, 2015;Cardona et al, 2016), the presented method works with arbitrary stimulation patterns, while it is only trained on a limited set of stimulation patterns. We used random stimulation patterns because we assume to cover most of the possible VEP responses.…”