  Event-related potentials (ERP) have been used to address a wide range of
research questions in neuroscience and cognitive psychology including selective
auditory attention. The recent progress in auditory attention decoding (AAD)
methods is based on algorithms that find a relation between the audio envelope
and the neurophysiological response. The most popular approach is based on the
reconstruction of the audio envelope based on EEG signals. However, these
methods are mainly based on the neurophysiological entrainment to physical
attributes of the sensory stimulus and are generally limited by a long
detection window. This study proposes a novel approach to auditory attention
decoding by looking at higher-level cognitive responses to natural speech. To
investigate if natural speech events elicit cognitive ERP components and how
these components are affected by attention mechanisms, we designed a series of
four experimental paradigms with increasing complexity: a word category oddball
paradigm, a word category oddball paradigm with competing speakers, and
competing speech streams with and without specific targets. We recorded the
electroencephalogram (EEG) from 32 scalp electrodes and 12 in-ear electrodes
(ear-EEG) from 24 participants. A cognitive ERP component, which we believe is
related to the well-known P3b component, was observed at parietal electrode
sites with a latency of approximately 620 ms. The component is statistically
most significant for the simplest paradigm and gradually decreases in strength
with increasing complexity of the paradigm. We also show that the component can
be observed in the in-ear EEG signals by using spatial filtering. The cognitive
component elicited by auditory attention may contribute to decoding auditory
attention from electrophysiological recordings and its presence in the ear-EEG
signals is promising for future applications within hearing aids.
