Acoustic predictability has been shown to affect auditory stream segregation, while
linguistic predictability is known to be an important factor in speech comprehension.
We tested the effects of linguistic predictability on auditory stream segregation
and target detection by assessing the event‐related potentials elicited by targets
and distractors in participants presented with two concurrent speech streams. The
linguistic cues of predictability varied over four levels. In the three real speech
conditions, natural speech was presented with intact phonotactics and sentence prosody:
normal speech, word‐salad (randomized word order within each sentence), and pseudo‐words
(randomized syllable order within each sentence). The fourth (control) condition delivered
a spectrally rotated version of the normal speech condition. Participants were instructed
to attend one stream and respond to the natural cough sounds embedded in it. Coughs
were present in both streams, serving as targets in the attended and as distractors
in the unattended stream. We expected improved target detection with increasing linguistic
predictability. The target‐related N2b component's amplitude monotonically increased
from the pseudo‐word to the word‐salad and normal speech condition, while no predictability
effects were observed for the P3b amplitude or for behavioral responses. The dissociation
between the N2b and P3b/behavioral effect suggests that while linguistic predictability
enhanced the process of classifying stimuli as potential targets, this did not affect
their detection. Furthermore, the observed nonmonotonic distractor N2 (probably MMN)
amplitude increase with increasing linguistic predictability is compatible with the
notion that linguistic predictability can modulate auditory stream segregation and/or
stream selection.
