Oddball paradigm complexity in multi-token auditory evoked potentials.

We developed and tested a series of novel and increasingly complex multi-token electrophysiology paradigms for evoking the auditory P3 response. The primary goal was to evaluate the degree to which more complex discrimination tasks and listening environments - which are more likely to engage the types of neural processing used in real-world speech-in-noise situations - could still evoke a robust P3 response. If so, this opens the possibility of such a paradigm making up part of the toolkit for a brain-behavioral approach to improve understanding of speech processing. Fourteen normal-hearing adults were tested using four different auditory paradigms consisting of 5 tokens, 20 tokens, 160 tokens, or 160 tokens with background babble. Stimuli were naturally produced consonant-vowel tokens varying in consonant (/d/, /b/, /g/, /v/, and /ð/; all conditions), vowel (/ɑ/, /u/, /i/, and /ɜr/; 20- and 160-token conditions), and talker (4 female, 4 male; 160-token conditions only). All four conditions evoked robust neural responses, and all peaks had visible differences across conditions. However, the more exogenous auditory evoked potentials (N1 and P2) were primarily affected not by overall complexity but by the presence of background noise specifically, the presence of which was associated with longer latencies and smaller amplitudes. The more endogenous P3 peak, as well as the paradigm behavioral measures, revealed a more graded effect of overall paradigm complexity, rather than the background noise dominating the other factors. Our conclusion was that all four complex auditory paradigms, including the most complex (160 distinct consonant-vowel tokens presented in background babble), are viable means of stimulating N1-P2 and N2b-P3 auditory evoked responses and may therefore be useful in brain-behavioral approaches to understanding speech perception in noise.