Modeling variability in cortical representations of human complex sound perception

This study investigated methodological (task, stimulus) and intersubject variability in the cortical representation of auditory processing of complex sounds, including speech. Subjects were adult seizure patients undergoing left hemisphere electrocortical mapping (ECM). We tested auditory discrimination of complex sounds, including frequency-modulated tones and speech syllables (digitized, synthesized) contrasted by phonetic features and lexical status. To measure task effects, auditory comprehension was also tested. Within- and across-patient differences in the distribution of deficits induced by ECM were modeled statistically using the recently developed method of Template Mixture Modeling. Cortical representations of auditory discrimination were smaller, more localized, and less variable across subjects than auditory comprehension. Stimulus effects were observed only for speech-tone contrasts. When tasks and stimuli were held constant, two auditory discrimination centers were identified in the posterior temporal lobe. There was also an interaction between task and intersubject effects, with more intersubject variability in cortical maps of auditory comprehension than auditory discrimination. These results demonstrate the utility of using the statistical modeling approach of Template Mixture Modeling to quantify sources of variability in cortical functional organization.