Chirp Speech: A Novel Approach for Studying Disordered Speech Processing in Children

     Clinical conditions that are marked by deficits in speech comprehension could potentially involve disordered processing at multiple levels of the speech processing hierarchy, from the central auditory nervous system through to cortical language networks. A range of event-related potentials exist that can index neural operations at all of these levels, but differences in the protocols required to measure them make comprehensive testing difficult. Chirp Speech is a novel method that combines natural speech with acoustic chirps to overcome this limitation. Chirps (i.e., brief upward frequency sweeps) have long been recognized to accommodate for the basilar membrane delay in acoustic transduction and thereby increase the detectability of early auditory evoked responses. Chirp Speech leverages this observation through acoustic engineering to optimize speech EEG responses while maintaining intelligibility.
     Using a sample of 29 children (16 typically-developing, 13 with listening difficulties), Chirp Speech successfully evoked a spectrum of auditory and cognitive responses ranging from the brainstem to cortical language processing. Post-auricular muscle artifacts and poor target word detection rates posed challenges for the measurement of the MLR and P300, respectively. Group differences in the scalp distribution of the N400 suggest altered semantic integration in children with LiD. Chirp Speech therefore effectively evokes a range of responses along the central auditory hierarchy, as well as responses associated with cognitive operations like selective attention, working memory, and language processing. The method is promising for patient populations with auditory deficits that involve contributions from the central nervous system.