SSVEP at Single and Beating Frequencies Utilizing Perceptual Insights
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2012-06-29
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en
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Abstract
Steady state visual evoked potentials (SSVEP) are widely used in EEG research as they offer a relatively high
signal to noise ratio allowing the investigation of visual processing at the cortical level. When the eyes are
presented with a flickering stimulus (up to 100Hz), the visual cortex generates a response oscillating at the
same fundamental frequency as the stimulus. For research purposes, these stimuli always had the goal of
eliciting a sufficiently strong EEG response. As a negative result, these stimuli are annoying to most users
and even become dangerous in regard to photosensitive epilepsy. Results from psychophysical research were
used to generate flickering stimuli which are around the human perception threshold for flickering lights. It is
shown for multiple frequencies that eliciting an SSVEP response with stimuli below the perception threshold is
possible. The human sensitivity to low frequency flicker makes it difficult to elicit an SSVEP response around
the perception threshold. Therefore, we tried generating waves combining two higher frequencies and using
the non-linearity of the human visual system to generate a sub-harmonic beating frequency. We attempted to
elicit an 8Hz response by using the sum wave of n*8Hz and (n+1)*8Hz (where n is a positive integer). Keywords: SSVEP, modulation depth, frequency, repetitive visual stimuli, EEG, beating frequency
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Faculteit der Sociale Wetenschappen