Frequency detection in Medium and High frequency SSVEP based Brain Computer Interface systems by scaling of sine-curve fit amplitudes

This study provides us a method for the frequency detection in Medium and High frequency SSVEP. We investigated the SSVEP response for 8 Hz (Low frequency), 14 Hz (Medium frequency), and 28 Hz (High frequency). Our results showed that the SSVEP responses are stronger in Low frequency region than that of Medium and High frequency regions indicating that Medium and High frequencies are difficult to detect in presence of Low frequencies. We used sine-curve fit amplitudes to find the responses at the stimulating frequencies. Then by scaling those amplitudes using z-score we can detect Medium and High frequencies even in the presence of Low frequencies. This method also detects frequency with an accuracy of 86% within 0.5 sec after on set.