Intracranial electrophysiology of spectrally degraded speech in the human cortex

This study used intracranial electroencephalography (iEEG) to investigate cortical processing of spectrally degraded speech.MethodsParticipants were adult neurosurgical epilepsy patients. Stimuli were utterances /aba/ and /ada/, spectrally degraded using a noise vocoder (1–4 bands) or presented without vocoding. The stimuli were presented in a two-alternative forced choice task. Cortical activity was recorded using depth and subdural iEEG electrodes. Electrode coverage included auditory core in posteromedial Heschl’s gyrus (HGPM), superior temporal gyrus (STG), ventral and dorsal auditory-related areas, and prefrontal and sensorimotor cortex. Analysis focused on high gamma (70–150 Hz) power augmentation and alpha (8–14 Hz) suppression.ResultsChance task performance occurred with 1–2 spectral bands and was near-ceiling for clear stimuli. Performance was variable with 3–4 bands, permitting identification of good and poor performers. There was no relationship between task performance and participants demographic, audiometric, neuropsychological, or clinical profiles. Several response patterns were identified based on magnitude and differences between stimulus conditions. HGPM responded strongly to all stimuli. A preference for clear speech emerged within non-core auditory cortex. Good performers typically had strong responses to all stimuli along the dorsal stream, including posterior STG, supramarginal, and precentral gyrus; a minority of sites in STG and supramargi...
Source: Frontiers in Human Neuroscience - Category: Neuroscience Source Type: research