A binaural implementation of the Hearing Aid Speech Perception Index (HASPI)

Introduction: The Hearing Aid Speech Perception Index version 2 (HASPI v2) is an intrusive speech intelligibility metric fitted to the intelligibility of sentence stimuli presented monaurally over headphones. It compares the time-frequency envelope modulation of a degraded signal, processed through a peripheral model matched to the subject’s audiogram, to the envelope modulation of an unprocessed noise-free signal processed through a normal-hearing (NH) peripheral model. This paper presents a binaural extension of HASPI v2. Methods: The binaural modifications are increasing the indicated hearing loss and providing a model of binaural interaction. The binaural HASPI was fit to binaural sentence-level intelligibility scores for NH and hearing-impaired (HI) subjects. The experimental conditions comprised combinations of room acoustics, spatial source configuration, noise, and simulated hearing-aid processing. Results: The Pearson correlation coefficients between the binaural HASPI predictions and the observed binaural intelligibility scores were 0.982 for the NH group, 0.981 for the HI group, and 0.983 for the combined groups. The corresponding RMS errors for intelligibility scores on a 0 to 1 scale were 0.050, 0.049, and 0.049. Discussion and Conclusions: The accuracy of the binaural HASPI is similar for HI and NH subjects. The accuracy compares favorably to that of existing binaural metrics.