Pinna shape similarity from excitation-inhibition patterns

This study assesses pinna shape similarity using excitation-inhibition (EI) patterns as a compact feature embedding of interaural spectral symmetry, motivated by auditory brainstem models. Pinna-related impulse responses were extracted from head-related impulse responses (HRIRs) along the median plane and converted into EI patterns. Ear similarity was quantified with Euclidean distances over EI peak values. Clustering of 144 individuals first separated them into spectral clusters (S-clusters) based on interaural spectral difference (ISD), distinguishing spectrally balanced from imbalanced ears. To isolate morphology from spectral asymmetry, the 119 individuals with balanced ISD were re-clustered into five morphological clusters (M-clusters). Representative average ear shapes (RAES) were derived for each M-cluster and used to synthesise HRIRs with a common head and torso but different pinna morphologies. A virtual listening experiment provided a preliminary perceptual test of whether these EI-derived differences affected median plane elevation localisation. Listeners who achieved reliable externalisation showed reduced accuracy when the RAES had larger conchae than their own ears, with errors increasing with concha antihelix valley to intertragic notch mismatch. These results suggest that EI-based clustering captures pinna morphology relevant to elevation localisation.