Optimal spatial filtering for auditory steady-state response detection using high-density EEG

Using periodic auditory stimuli, it is possible to evoke so-called auditory steady-state responses (ASSRs) in the brain, which can be measured using electroencephalography (EEG). They can be used to objectively estimate frequency-specific hearing thresholds, which is especially useful for early hearing assessment in newborns. The main problem is the extremely low signal-to-noise ratio (SNR), necessitating long measurements of up to an hour for a full audiometric assessment. To speed up the detection, we apply a linear spatial filter to the multi-channel EEG measurements, resulting in a new ´virtual´ channel with optimal SNR. To ensure robustness, we then consider a hybrid ASSR detection method in which the original EEG channels are complemented with this virtual channel. The addition of this virtual channel successfully speeds up the detection of ASSRs by over 15 %. Furthermore our method not only speeds up the detection, but also greatly improves its sensitivity, in particular in the (clinically most relevant) lowest SNR scenarios. This could help reduce the gap that still exists between behaviourally and objectively obtained hearing thresholds.